VIN
CIN
3 x 10 PF
RFBT
CFF 4.7 nF (OPT)
See Table
CSS
0.47 PF
(OPT)
RFBB
See Table COUT
2 x 330 PF
LMZ23608
SH
SS
FB
SYNC
EN
PGND
VOUT
AGND
Enable
VIN
VOUT
Share
Clock
0 1 2 3 4 5 6 7 8
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
Product
Folder
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LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
LMZ23608 8-A SIMPLE SWITCHER
®
Power Module With 36-V Maximum Input Voltage and
Current Sharing
1 Features 2 Applications
1• Integrated Shielded Inductor • Point-of-load Conversions from 12-V and 24-V
Input Rail
• Simple PCB Layout • Time-Critical Projects
• Frequency Synchronization Input (350 kHz to 600
kHz) • Space Constrained and High Thermal
Requirement Applications
• Current Sharing Capability • Negative Output Voltage Applications
• Flexible Start-up Sequencing Using External Soft- (See AN-2027 SNVA425)
Start, Tracking and Precision Enable
• Protection Against Inrush Currents and Faults 3 Description
Such as Input UVLO and Output Short Circuit The LMZ23608 SIMPLE SWITCHER®power module
• Junction Temperature Range –40°C to 125°C is an easy-to-use step-down DC-DC solution capable
• Single Exposed Pad and Standard Pinout for Easy of driving up to 8-A load. The LMZ23608 is available
Mounting and Manufacturing in an innovative package that enhances thermal
performance and allows for hand or machine
• Fully Enabled for WEBENCH®Power Designer soldering.
• Pin Compatible With LMZ22010/08, The LMZ23608 can accept an input voltage rail
LMZ12010/08, LMZ23610/06H, and between 6 V and 36 V and can deliver an adjustable
LMZ13610/08/06H and highly accurate output voltage as low as 0.8 V.
• Electrical Specifications The LMZ23608 only requires two external resistors
– 40-W Maximum Total Output Power and three external capacitors to complete the power
solution.
– Up to 8-A Output Current
– Input Voltage Range 6 V to 36 V The LMZ23608 is a reliable and robust design with
the following protection features: thermal shutdown,
– Output Voltage Range 0.8 V to 6 V input undervoltage lockout, output overvoltage
– Efficiency up to 92% protection, short circuit protection, output current limit,
• Performance Benefits and allows start-up into a prebiased output. The sync
input allows synchronization over the 350 to 600-kHz
– High Efficiency Reduces System Heat switching frequency range.
Generation
– Low Radiated Emissions (EMI) Tested to Device Information(1)(2)
EN55022 Class B Standard PART NUMBER PACKAGE BODY SIZE (NOM)
– Only 7 External Components LMZ23608 NDY (11) 15.00 mm × 15.00 mm
– Low Output Voltage Ripple (1) For all available packages, see the orderable addendum at
– No External Heat Sink Required the end of the data sheet.
(2) Peak reflow temperature equals 245°C. See SNAA214 for
– Simple Current Sharing for Higher Current more details.
Applications
NOTE: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B,
tested on Evaluation Board with EMI configuration
Simplified Application Schematic Efficiency 3.3-V Output at 25°C
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
Table of Contents
1 Features.................................................................. 18 Application and Implementation ........................ 18
8.1 Application Information............................................ 18
2 Applications ........................................................... 18.2 Typical Application ................................................. 18
3 Description............................................................. 19 Power Supply Recommendations...................... 24
4 Revision History..................................................... 210 Layout................................................................... 24
5 Pin Configuration and Functions......................... 310.1 Layout Guidelines ................................................. 24
6 Specifications......................................................... 410.2 Layout Examples................................................... 25
6.1 Absolute Maximum Ratings ...................................... 410.3 Power Dissipation and Thermal Considerations... 26
6.2 ESD Ratings.............................................................. 410.4 Power Module SMT Guidelines ............................ 27
6.3 Recommended Operating Conditions....................... 411 Device and Documentation Support................. 29
6.4 Thermal Information.................................................. 411.1 Device Support...................................................... 29
6.5 Electrical Characteristics........................................... 511.2 Documentation Support ........................................ 29
6.6 Typical Characteristics ............................................. 611.3 Community Resources.......................................... 29
7 Detailed Description............................................ 14 11.4 Trademarks........................................................... 29
7.1 Overview................................................................. 14 11.5 Electrostatic Discharge Caution............................ 29
7.2 Functional Block Diagram....................................... 14 11.6 Glossary................................................................ 29
7.3 Feature Description................................................. 14 12 Mechanical, Packaging, and Orderable
7.4 Device Functional Modes........................................ 17 Information........................................................... 30
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision F (October 2013) to Revision G Page
• Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes,Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
• Deleted Easy-to-Use PFM 7-Pin Package image .................................................................................................................. 1
Changes from Revision E (March 2013) to Revision F Page
• Deleted 12 mils....................................................................................................................................................................... 4
• Changed 12 mils................................................................................................................................................................... 24
• Changed 12 mils................................................................................................................................................................... 26
• Added Power Module SMT Guidelines................................................................................................................................. 27
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Product Folder Links: LMZ23608
PGND/EP
Connect to AGND 5 AGND
6 AGND
3 SYNC
1 VIN
2 VIN
4 EN
7 FB
SS
9SH
10 VOUT
11 VOUT
8
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
5 Pin Configuration and Functions
NDY Package
11-Pin
Top View
Pin Functions
PIN I/O DESCRIPTION
NAME NO.
AGND 5 Ground Analog Ground — Reference point for all stated voltages. Must be externally connected to
EP/PGND.
6
EN 4 Analog Enable — Input to the precision enable comparator. Rising threshold is 1.274 V typical. Once the
module is enabled, a 20-µA source current is internally activated to accommodate programmable
hysteresis.
FB 7 Analog Feedback — Internally connected to the regulation, overvoltage, and short circuit comparators. The
regulation reference point is 0.8 V at this input pin. Connect the feedback resistor divider between
the output and AGND to set the output voltage.
PGND — Ground Exposed Pad / Power Ground Electrical path for the power circuits within the module. — NOT
Internally connected to AGND / pin 5. Used to dissipate heat from the package during operation.
Must be electrically connected to pin 5 external to the package.
SH 9 Analog Share pin. Connect this to the share pin of other LMZ23608 modules to share the load between the
devices. One device must be configured as the master by connecting the FB normally. All other
devices must be configured as slaves by leaving their respective FB pins floating. Leave this pin
floating if not used, do not ground. See Design Steps section.
SS 8 Analog Soft-Start/Track input — To extend the 1.6-ms internal soft-start connect an external soft-start
capacitor. For tracking connect to an external resistive divider connected to a higher priority supply
rail. See Design Steps section.
SYNC 3 Analog Sync Input — Apply a CMOS logic level square wave whose frequency is between 350 kHz and
600 kHz to synchronize the PWM operating frequency to an external frequency source. When not
using synchronization this pin must be tied to ground. The module free running PWM frequency is
350 kHz.
VOUT 10 Power Output Voltage — Output from the internal inductor. Connect the output capacitor between this pin
and PGND.
11
VIN 1 Power Supply input — Nominal operating range is 6 V to 36 V. A small amount of internal capacitance is
contained within the package assembly. Additional external input capacitance is required between
2this pin and PGND.
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LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)(3)
MIN MAX UNIT
VIN to PGND –0.3 40 V
EN, SYNC to AGND –0.3 5.5 V
SS, FB, SH to AGND –0.3 2.5 V
AGND to PGND –0.3 0.3 V
Junction temperature 150 °C
Storage temperature, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) For soldering specifications: see product folder at www.ti.com and SNOA549
6.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions MIN MAX UNIT
VIN 6 36 V
EN, SYNC 0 5 V
Operation junction temperature −40 125 °C
6.4 Thermal Information LMZ23608
THERMAL METRIC(1) NDY UNIT
11 PINS
Natural Convection 9.9
RθJA Junction-to-ambient thermal resistance(2) 225 LFPM 6.8 °C/W
500 LFPM 5.2
RθJC(top) Junction-to-case (top) thermal resistance 1.0 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) Theta JA measured on a 3.0-in x 3.5-in 4-layer board, with 2-oz. copper on outer layers and 1-oz. copper on inner layers, two hundred
and ten thermal vias, and 2-W power dissipation. Refer to evaluation board application note layout diagrams.
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LMZ23608
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SNVS708G –MARCH 2011–REVISED AUGUST 2015
6.5 Electrical Characteristics
Limits are for TJ= 25°C unless otherwise specified. Minimum and Maximum limits are ensured through test, design or
statistical correlation. Typical values represent the most likely parametric norm at TJ= 25°C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: VIN = 12V, VOUT = 3.3V
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
SYSTEM PARAMETERS
ENABLE CONTROL
1.274
VEN EN threshold VEN rising V
over the junction temperature (TJ) range 1.096 1.452
of –40°C to +125°C
IEN-HYS EN hysteresis source current VEN > 1.274 V 13 µA
SOFT-START
50
ISS SS source current VSS = 0 V µA
over the junction temperature (TJ) range 40 60
of –40°C to +125°C
tSS Internal soft-start interval 1.6 ms
CURRENT LIMIT
ICL Current limit threshold DC average 10.5 A
INTERNAL SWITCHING OSCILLATOR
Free-running oscillator
fosc Sync input connected to ground 314 359 404 kHz
frequency
fsync Synchronization range Vsync = 3.3 Vp-p 314 600 kHz
Synchronization logic zero over the junction temperature (TJ) range
VIL-sync Relative to AGND 0.4 V
amplitude of –40°C to +125°C
Synchronization logic one over the junction temperature (TJ) range
VIH-sync Relative to AGND 1.8 V
amplitude of –40°C to +125°C
Synchronization duty cycle
SyncDC 15% 50% 85%
range
REGULATION AND OVERVOLTAGE COMPARATOR
0.795
VSS >+ 0.8 V
VFB In-regulation feedback voltage V
over the junction temperature (TJ) range
IO= 8 A 0.775 0.815
of –40°C to +125°C
Feedback over-voltage
VFB-OV 0.86 V
protection threshold
IFB Feedback input bias current 5 nA
Non-switching quiescent
IQSYNC = 3 V 3 mA
current
ISD Shutdown quiescent current VEN = 0 V 32 μA
Dmax Maximum duty factor 85%
THERMAL CHARACTERISTICS
TSD Thermal shutdown Rising 165 °C
TSD-HYST Thermal shutdown hysteresis Falling 15 °C
PERFORMANCE PARAMETERS(3)
ΔVOOutput voltage ripple BW at 20 MHz 24 mVPP
ΔVO/ΔVIN Line regulation VIN = 12V to 20 V, IOUT= 8 A ±0.2%
ΔVO/ΔIOUT Load regulation VIN = 12 V, IOUT= 0.001 A to 8 A 1 mV/A
ηPeak efficiency VIN = 12 V, VOUT = 3.3 V, IOUT = 5 A 89.5%
ηFull load efficiency VIN = 12 V, VOUT = 3.3 V, IOUT = 8 A 88.5%
(1) Minimum and Maximum limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through
correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
(2) Typical numbers are at 25°C and represent the most likely parametric norm.
(3) Refer to BOM in Table 1.
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 5
Product Folder Links: LMZ23608
0 1 2 3 4 5 6 7 8
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
8 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
8 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
6.6 Typical Characteristics
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
Figure 1. Efficiency 50-V Output at 25°C Figure 2. Dissipation 5-V Output at 25°C
Figure 3. Efficiency 3.3-V Output at 25°C Figure 4. Dissipation 3.3-V Output at 25°C
Figure 5. Efficiency 2.5-V Output at 25°C Figure 6. Dissipation 2.5-V Output at 25°C
6Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
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0 1 2 3 4 5 6 7 8
0
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
Figure 7. Efficiency 1.8-V Output at 25°C Figure 8. Dissipation 1.8-V Output at 25°C
Figure 9. Efficiency 1.5-V Output at 25°C Figure 10. Dissipation 1.5-V Output at 25°C
Figure 11. Efficiency 1.2-V Output at 25°C Figure 12. Dissipation 1.2-V Output at 25°C
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Links: LMZ23608
0 1 2 3 4 5 6 7 8
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
8 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
8 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
0
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
Figure 13. Efficiency 1-V Output at 25°C Figure 14. Dissipation 1-V Output at 25°C
Figure 15. Efficiency 5-V Output at 85°C Figure 16. Dissipation 5-V Output at 85°C
Figure 17. Efficiency 3.3-V Output at 85°C Figure 18. Dissipation 3.3-V Output at 85°C
8Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LMZ23608
0 1 2 3 4 5 6 7 8
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
Figure 19. Efficiency 2.5-V Output at 85°C Figure 20. Dissipation 2.5-V Output at 85°C
Figure 21. Efficiency 1.8-V Output at 85°C Figure 22. Dissipation 1.8-V Output at 85°C
Figure 23. Efficiency 1.5-V Output at 85°C Figure 24. Dissipation 1.5-V Output at 85°C
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 9
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0 1 2 3 4 5 6 7 8
0.998
0.999
1.000
1.001
1.002
NORMALIZED VOUT (V/V)
OUTPUT CURRENT (A)
6 Vin
8 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
36 Vin
20 30 40 50 60 70 80 90 100110120
0
2
4
6
8
10
MAXIMUM OUTPUT CURRENT (A)
TEMPERATURE (C)
JA = 9.9 °C/W
JA = 6.8 °C/W
JA = 5.2 °C/W
0 1 2 3 4 5 6 7 8
0
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
2
4
6
8
10
12
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
0 1 2 3 4 5 6 7 8
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36Vin
0 1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
DISSIPATION (W)
OUTPUT CURRENT (A)
6 Vin
10 Vin
12 Vin
16 Vin
20 Vin
24 Vin
30 Vin
36 Vin
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
Figure 25. Efficiency 1.2-V Output at 85°C Figure 26. Dissipation 1.2-V Output at 85°C
Figure 27. Efficiency 1-V Output at 85°C Figure 28. Dissipation 1-V Output at 85°C
VOUT = 3.3 V VIN = 24 V, VOUT = 5 V
Figure 29. Normalized Line and Load Regulation Figure 30. Thermal Derating
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20 30 40 50 60 70 80 90 100110120
0
2
4
6
8
10
MAXIMUM OUTPUT CURRENT (A)
TEMPERATURE (C)
JA = 9.9 °C/W
JA = 6.8 °C/W
JA = 5.2 °C/W
0 2 4 6 8 10 12
3
6
9
12
15
18
21
24
27
30
THETA JA (°C/W)
COPPER AREA (in2)
2 Layer 0 LFPM
2 Layer 225 LFPM
4 Layer 0 LFPM
4 Layer 225 LFPM
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
VIN = 24 V, VOUT = 3.3 V
Figure 31. Thermal Derating Figure 32. θJA vs Copper Heat Sinking Area
12 VIN, 5 VOUT at Full Load, BW = 20 MHz 12 VIN, 5 VOUT at Full Load, BW = 250 MHz
Figure 33. Output Ripple Figure 34. Output Ripple
12 VIN, 3.3 VOUT at Full Load, BW = 250 MHz
12 VIN, 3.3 VOUT at Full Load, BW = 20 MHz
Figure 36. Output Ripple
Figure 35. Output Ripple
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5 10 15 20
0
2
4
6
8
10
12
14
16
CURRENT (A)
INPUT VOLTAGE (V)
Output Current
Input Current
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
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Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
12 VIN, 1.2 VOUT at Full Load, BW = 250 MHz
12 VIN, 1.2 VOUT at Full Load, BW = 20 MHz
Figure 38. Output Ripple
Figure 37. Output Ripple
12 VIN, 5 VOUT 1- to 8-A Step 12 VIN, 3.3 VOUT 1- to 8-A Step
Figure 39. Transient Response Figure 40. Transient Response
12 VIN, 1.2 VOUT 1- to 8-A Step
Figure 41. Transient Response Figure 42. Short Circuit Current vs Input Voltage
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Typical Characteristics (continued)
Unless otherwise specified, the following conditions apply: VIN = 12 V; CIN = 3 x 10 μF + 47-nF X7R Ceramic; COUT = 2 x 330-
μF Specialty Polymer + 47-µF Ceramic + 47-nF Ceramic; CFF = 4.7 nF; TA= 25°C for waveforms. All indicated temperatures
are ambient.
No CSS CSS = 0.47 µF
Figure 43. 3.3 VOUT Soft-Start Figure 44. 3.3 VOUT Soft-Start
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7 Detailed Description
7.1 Overview
The architecture used is an internally compensated emulated peak current mode control, based on a monolithic
synchronous SIMPLE SWITCHER core capable of supporting high load currents. The output voltage is
maintained through feedback compared with an internal 0.8-V reference. For emulated peak current-mode, the
valley current is sampled on the down-slope of the inductor current. This is used as the DC value of current to
start the next cycle. The primary application for emulated peak current-mode is high input voltage to low output
voltage operating at a narrow duty cycle. By sampling the inductor current at the end of the switching cycle and
adding an external ramp, the minimum ON-time can be significantly reduced, without the need for blanking or
filtering which is normally required for peak current-mode control.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Synchronization Input
The PWM switching frequency can be synchronized to an external frequency source. The PWM switching will be
in phase with the external frequency source. If this feature is not used, connect this input either directly to
ground, or connect to ground through a resistor of 1.5 kΩor less. The allowed synchronization frequency range
is 314 kHz to 600 kHz. The typical input threshold is 1.4 V. Ideally, the input clock must overdrive the threshold
by a factor of 2, so direct drive from 3.3-V logic through a 1.5-kΩor less Thevenin source resistance is
recommended. Applying a sustained logic 1 corresponds to 0-Hz PWM frequency and will cause the module to
stop switching.
7.3.2 Current Sharing
When a load current higher than 8 A is required by the application, the LMZ23608 can be configured to share the
load between multiple devices. To share the load current between the devices, connect the SH pin of all current
sharing LMZ23608 modules. One device must be configured as the master by connecting FB normally. All other
devices must be configured as slaves by leaving their respective FB pins floating. The modules must be
synchronized by a clock signal to avoid beat frequencies in the output voltage caused by small differences in the
internal 359-kHz clock. If the modules are not synchronized, the magnitude of the ripple voltage will depend on
the phase relationship of the internal clocks. The external synchronizing clocks can be in phase for all modules,
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CIN_BYP
RFBT
CSS
RFBB
COUT_BYP
SH
SS
FB
SYNC
EN
PGND
VOUT
AGND
Enable
VIN
VOUT
Share
Clk
MASTER LOAD
CIN_BYP COUT_BYP
SH
SS
FB
SYNC
EN
PGND
AGND
Enable
VIN
VOUT
Share
Clk
SLAVE
VIN
CIN_BULK COUT_BULK
XX
LMZ23608
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SNVS708G –MARCH 2011–REVISED AUGUST 2015
Feature Description (continued)
or out of phase to reduce the current stress on the input and output capacitors. As an example, two modules can
be run 180 degrees out of phase, and three modules can be run 120 degrees out of phase. The VIN, VOUT,
PGND, and AGND pins must also be connected with low impedance paths. It is particularly important to pay
close attention to the layout of AGND and SH, as offsets in grounding or noise picked up from other devices will
be seen as a mismatch in current sharing and could cause noise issues.
Current sharing modules can be configured to share the same set of bulk input and output capacitors, while each
having their own local input and output bypass capacitors. A CIN_BYP >= 30 µF is still recommended for each
module that is connected in a current sharing configuration. A COUT_BYP consisting of 47-nF X7R ceramic
capacitor in parallel with a 22-µF ceramic capacitor is recommended to locally bypass the output voltage for each
module. These capacitors will provide local bypassing of high-frequency switched currents.
In a current sharing system using two or more modules, the slaves have their error amp circuitry disconnected.
The master overrides the error amplifier outputs of the slaves. This signal is then compared to each module’s
individual current sense circuitry. Due to this, the current sense gain of the entire system increases according to
the number of modules slaved to the master. To compensate for this and ensure good stability, the total output
capacitance has to be increased. For example, two modules configured to provide 1.2 VOUT and 16 amps have a
required total bulk output capacitance of COUT_BULK = 2 × 450 µF (ESR 25 mΩ). This is a thirty six percent
increase in the required output capacitance of a stand alone module. Up to 6 modules can be connected in
parallel for loads up to 48 A. For more information on current sharing refer to AN-2093 (SNVA460).
Figure 45. Current Sharing Example Schematic
Figure 46. Output Voltage Ripple of Two Modules With Figure 47. Output Voltage Ripple of Two Modules With
Synchronization Clocks in Phase Synchronization Clocks 180 Degrees Out of Phase
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Feature Description (continued)
7.3.3 Output Overvoltage Protection
If the voltage at FB is greater than a 0.86-V internal reference, the output of the error amplifier is pulled toward
ground, causing VOUT to fall.
7.3.4 Current Limit
The LMZ23608 is protected by both low-side (LS) and high-side (HS) current limit circuitry. The LS current limit
detection is carried out during the OFF-time by monitoring the current through the LS synchronous MOSFET.
Referring to the Functional Block Diagram, when the top MOSFET is turned off, the inductor current flows
through the load, the PGND pin and the internal synchronous MOSFET. If this current exceeds 13 A (typical), the
current limit comparator disables the start of the next switching period. Switching cycles are prohibited until
current drops below the limit.
NOTE
DC current limit is dependent on duty cycle as illustrated in the graph in the Typical
Characteristics section.
The HS current limit monitors the current of top side MOSFET. Once HS current limit is detected (16 A typical) ,
the HS MOSFET is shutoff immediately, until the next cycle. Exceeding HS current limit causes VOUT to fall.
Typical behavior of exceeding LS current limit is that fSW drops to 1/2 of the operating frequency.
7.3.5 Thermal Protection
The junction temperature of the LMZ23608 must not be allowed to exceed its maximum ratings. Thermal
protection is implemented by an internal Thermal Shutdown circuit which activates at 165°C (typical) causing the
device to enter a low power standby state. In this state the main MOSFET remains off causing VOUT to fall, and
additionally the CSS capacitor is discharged to ground. Thermal protection helps prevent catastrophic failures for
accidental device overheating. When the junction temperature falls back below 150°C (typical hysteresis = 15°C)
the SS pin is released, VOUT rises smoothly, and normal operation resumes.
Applications requiring maximum output current especially those at high input voltage may require additional
derating at elevated temperatures.
7.3.6 Prebiased Start-Up
The LMZ23608 will properly start up into a prebiased output. This start-up situation is common in multiple rail
logic applications where current paths may exist between different power rails during the start-up sequence. The
following scope capture shows proper behavior in this mode. Trace one is Enable going high. Trace two is 1.8-V
prebias rising to 3.3 V. Trace three is the SS voltage with a CSS= 0.47 µF. Rise-time determined by CSS.
Figure 48. Prebiased Start-Up
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7.4 Device Functional Modes
7.4.1 Discontinuous Conduction and Continuous Conduction Modes
At light load the regulator will operate in discontinuous conduction mode (DCM). With load currents above the
critical conduction point, it will operate in continuous conduction mode (CCM). When operating in DCM, inductor
current is maintained to an average value equaling IOUT. In DCM the low-side switch will turn off when the
inductor current falls to zero, this causes the inductor current to resonate. Although it is in DCM, the current is
allowed to go slightly negative to charge the bootstrap capacitor.
In CCM, current flows through the inductor through the entire switching cycle and never falls to zero during the
OFF-time.
Following is a comparison pair of waveforms showing both the CCM (upper) and DCM operating modes.
VIN = 12 V, VO= 3.3 V, IO= 3 A / 0.3 A
Figure 49. CCM and DCM Operating Modes
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CIN1
RFBT
CSS
RFBB
SH
SS
FB
SYNC
EN
PGND
VOUT
AGND
VIN
VOUT
Share
Clk
LMZ23608
LOAD
VIN
CIN6
(OPT) CO3,4
CIN5
(OPT)
+
CIN2,3,4 CO1
(OPT) CO2
(OPT)
CO5
(OPT)
RSYNC
RENB
RENT
D1
5.1V
(OPT)
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LMZ23608 is a step-down DC-to-DC power module. It is typically used to convert a higher DC voltage to a
lower DC voltage with a maximum output current of 8 A. The following design procedure can be used to select
components for the LMZ23608. Alternately, the WEBENCH software may be used to generate complete designs.
When generating a design, the WEBENCH software uses iterative design procedure and accesses
comprehensive databases of components. Please go to www.ti.com for more details.
8.2 Typical Application
Figure 50. Typical Application Schematic Diagram
8.2.1 Design Requirements
For this example the following application parameters exist.
• VIN Range = Up to 36 V
• VOUT =0.8Vto6V
• IOUT =8A
8.2.2 Detailed Design Procedure
8.2.2.1 Design Steps
The LMZ23608 is fully supported by WEBENCH which offers: component selection, electrical and thermal
simulations. Additionally, there are both evaluation and demonstration boards that may be used as a starting
point for design. The following list of steps can be used to manually design the LMZ23608 application.
All references to values refer to the typical applications schematic Table 1.
1. Select minimum operating VIN with enable divider resistors
2. Program VOUT with FB resistor divider selection
3. Select COUT
4. Select CIN
5. Determine module power dissipation
6. Layout PCB for required thermal performance
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ENABLE
2.0M
13 PA
INT-VCC (5V)
1.274V
RUN
12.7k
RENB
42.2k
RENT
VIN
100:
RENH
5.1V
LMZ23608
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SNVS708G –MARCH 2011–REVISED AUGUST 2015
Typical Application (continued)
8.2.2.2 Enable Divider, RENT, RENB and RENH Selection
Internal to the module is a 2-MΩpullup resistor connected from VIN to Enable. For applications not requiring
precision undervoltage lockout (UVLO), the Enable input may be left open circuit and the internal resistor will
always enable the module. In such case, the internal UVLO occurs typically at 4.3 V (VIN rising).
In applications with separate supervisory circuits Enable can be directly interfaced to a logic source. In the case
of sequencing supplies, the divider is connected to a rail that becomes active earlier in the power-up cycle than
the LMZ23608 output rail.
Enable provides a precise 1.274-V threshold to allow direct logic drive or connection to a voltage divider from a
higher enable voltage such as VIN. Additionally there is 13 μA (typical) of switched offset current allowing
programmable hysteresis. See Figure 51.
The function of the enable divider is to allow the designer to choose an input voltage below which the circuit will
be disabled. This implements the feature of a programmable UVLO. The two resistors must be chosen based on
the following ratio:
RENT / RENB = (VIN UVLO / 1.274 V) – 1 (1)
The LMZ23608 typical application shows 12.7 kΩfor RENB and 42.2 kΩfor RENT resulting in a rising UVLO of
5.51 V.
NOTE
This divider presents 4.62 V to the EN input when VIN is raised to 20 V.
This upper voltage must always be checked, making sure that it never exceeds the Abs Max 5.5-V limit for
Enable. A 5.1-V Zener clamp can be applied in cases where the upper voltage would exceed the EN input's
range of operation. The Zener clamp is not required if the target application prohibits the maximum Enable input
voltage from being exceeded.
Additional enable voltage hysteresis can be added with the inclusion of RENH. It is possible to select values for
RENT and RENB such that RENH is a value of zero allowing it to be omitted from the design.
Rising threshold can be calculated as follows:
VEN(rising) = 1.274 ( 1 + (RENT|| 2 meg)/ RENB) (2)
Whereas the falling threshold level can be calculated using:
VEN(falling) = VEN(rising) – 13 µA ( RENT|| 2 meg || RENTB + RENH ) (3)
Figure 51. Enable Input Detail
8.2.2.3 Output Voltage Selection
Output voltage is determined by a divider of two resistors connected between VOUT and AGND. The midpoint of
the divider is connected to the FB input.
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Typical Application (continued)
The regulated output voltage determined by the external divider resistors RFBT and RFBB is:
VOUT = 0.795 V × (1 + RFBT / RFBB) (4)
Rearranging terms; the ratio of the feedback resistors for a desired output voltage is:
RFBT / RFBB = (VOUT / 0.795 V) – 1 (5)
These resistors must generally be chosen from values in the range of 1.0 kΩto 10.0 kΩ.
For VOUT = 0.8 V the FB pin can be connected to the output directly and RFBB can be set to 8.06 kΩto provide
minimum output load.
Table 1 lists the values for RFBT , and RFBB.
Table 1. Typical Application Bill of Materials
REF DES DESCRIPTION CASE SIZE MANUFACTURER MANUFACTURER P/N
U1 SIMPLE SWITCHER PFM-11 Texas Instruments LMZ23608TZ
CIN1,6 (OPT) 0.047 µF, 50 V, X7R 1206 Yageo America CC1206KRX7R9BB473
CIN2,3,4 10 µF, 50 V, X7R 1210 Taiyo Yuden UMK325BJ106MM-T
CIN5 (OPT) CAP, AL, 150 µF, 50 V Radial G Panasonic EEE-FK1H151P
CO1,5 (OPT) 0.047 µF, 50 V, X7R 1206 Yageo America CC1206KRX7R9BB473
CO2 (OPT) 47 µF, 10 V, X7R 1210 Murata GRM32ER61A476KE20L
CO3,4 330 μF, 6.3 V, 0.015 ΩCAPSMT_6_UE Kemet T520D337M006ATE015
RFBT 3.32 kΩ0805 Panasonic ERJ-6ENF3321V
RFBB 1.07 kΩ0805 Panasonic ERJ-6ENF1071V
RSYNC 1.50 kΩ0805 Vishay Dale CRCW08051K50FKEA
RENT 42.2 kΩ0805 Panasonic ERJ-6ENF4222V
RENB 12.7 kΩ0805 Panasonic ERJ-6ENF1272V
CSS 0.47 μF, ±10%, X7R, 16 V 0805 AVX 0805YC474KAT2A
D1 (OPT) 5.1 V, 0.5 W SOD-123 Diodes Inc. MMSZ5231BS-7-F
8.2.2.4 Soft-Start Capacitor Selection
Programmable soft-start permits the regulator to slowly ramp to its steady-state operating point after being
enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time.
Upon turnon, after all UVLO conditions have been passed, an internal 1.6-ms circuit slowly ramps the SS input to
implement internal soft start. If 1.6 ms is an adequate turnon time then the Css capacitor can be left unpopulated.
Longer soft-start periods are achieved by adding an external capacitor to this input.
Soft-start duration is given by the formula:
tSS = VREF × CSS / Iss = 0.795 V × CSS / 50 µA (6)
This equation can be rearranged as follows:
CSS = tSS × 50 μA / 0.795 V (7)
Using a 0.22-μF capacitor results in 3.5-ms typical soft-start duration; and 0.47 μF results in 7.5 ms typical. 0.47
μF is a recommended initial value.
As the soft-start input exceeds 0.795 V the output of the power stage will be in regulation and the 50-μA current
is deactivated. The following conditions will reset the soft-start capacitor by discharging the SS input to ground
with an internal current sink.
• The Enable input being pulled low
• A thermal shutdown condition
• VIN falling below 4.3 V (typical) and triggering the VCC UVLO
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7A
COUTt (0.165V - 7A x 0.003) x ( )
350e3
3.3V
t458 PF
Istep
COUTt
('VOUT - ISTEP x ESR) x ( )
fSW
VOUT
1.07k
Rfbb
2.26k
Rfbt
107
Rtkb
226
Rtkt
SS
3.3V Master
FB
2.5Vout
50 PA
Int VCC
LMZ23608
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SNVS708G –MARCH 2011–REVISED AUGUST 2015
8.2.2.5 Tracking Supply Divider Option
The tracking function allows the module to be connected as a slave supply to a primary voltage rail (often the
3.3-V system rail) where the slave module output voltage is lower than that of the master. Proper configuration
allows the slave rail to power up coincident with the master rail such that the voltage difference between the rails
during ramp-up is small (that is, < 0.15 V typical). The values for the tracking resistive divider must be selected
such that the effect of the internal 50-µA current source is minimized. In most cases the ratio of the tracking
divider resistors is the same as the ratio of the output voltage setting divider. Proper operation in tracking mode
dictates the soft-start time of the slave rail be shorter than the master rail; a condition that is easy to satisfy
because the CSS cap is replaced by RTKB. The tracking function is only supported for the power up interval of the
master supply; once the SS/TRK rises past 0.795 V the input is no longer enabled and the 50-µA internal current
source is switched off.
Figure 52. Tracking Option Input Detail
8.2.2.6 COUT Selection
None of the required COUT output capacitance is contained within the module. A minimum value ranging from 330
μF for 6-VOUT to 660 μF for 1.2-VOUT applications is required based on the values of internal compensation in the
error amplifier. These minimum values can be decreased if the effective capacitor ESR is higher than 15 mΩ.
A Low ESR (15-mΩ) tantalum, organic semiconductor or specialty polymer capacitor types in parallel with a 47-
nF X7R ceramic capacitor for high frequency noise reduction is recommended for obtaining lowest ripple. The
output capacitor COUT may consist of several capacitors in parallel placed in close proximity to the module. The
output voltage ripple of the module depends on the equivalent series resistance (ESR) of the capacitor bank, and
can be calculated by multiplying the ripple current of the module by the effective impedance of your chosen
output capacitors (for ripple current calculation, see Equation 14). Electrolytic capacitors will have large ESR and
lead to larger output ripple than ceramic or polymer types. For this reason a combination of ceramic and polymer
capacitors is recommended for low output ripple performance.
The output capacitor assembly must also meet the worst case ripple current rating of ΔiL, as calculated in
Equation 14 below. Loop response verification is also valuable to confirm closed loop behavior.
For applications with dynamic load steps; the following equation provides a good first pass approximation of COUT
for load transient requirements.
(8)
For 12 VIN, 3.3 VOUT, a transient voltage of 5% of VOUT = 0.165 V (ΔVOUT), a 7-A load step (ISTEP), an output
capacitor effective ESR of 3 mΩ, and a switching frequency of 350 kHz (fSW):
(9)
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'iL =(VIN - VOUT) x D
L x fSW
IDCB = (VIN - VOUT) x D
2 x L x fSW
CIN 8350 kHz x 200mV 8 22.4µF
3.3V
12V
3.3V
12V ¹
·
©
§
¹
·
©
§
8A x x 1 -
CIN 8IOUT x D x (1 - D)
fSW x 'VIN
ICIN-RMS = IOUT xD(1-D)
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
NOTE
The stability requirement for minimum output capacitance must always be met.
One recommended output capacitor combination is two 330-μF, 15-mΩESR tantalum polymer capacitors
connected in parallel with a 47-µF 6.3-V X5R ceramic. This combination provides excellent performance that may
exceed the requirements of certain applications. Additionally some small 47-nF ceramic capacitors can be used
for high-frequency EMI suppression.
8.2.2.7 CIN Selection
The LMZ23608 module contains two internal ceramic input capacitors. Additional input capacitance is required
external to the module to handle the input ripple current of the application. The input capacitor can be several
capacitors in parallel. This input capacitance must be located in very close proximity to the module. Input
capacitor selection is generally directed to satisfy the input ripple current requirements rather than by
capacitance value. Input ripple current rating is dictated by the equation:
where
• D ≊VOUT / VIN (10)
As a point of reference, the worst case ripple current will occur when the module is presented with full load
current and when VIN = 2 × VOUT.
Recommended minimum input capacitance is 30-µF X7R (or X5R) ceramic with a voltage rating at least 25%
higher than the maximum applied input voltage for the application. TI also recommends to pay attention to the
voltage and temperature derating of the capacitor selected.
NOTE
Ripple current rating of ceramic capacitors may be missing from the capacitor data sheet
and you may have to contact the capacitor manufacturer for this parameter.
If the system design requires a certain minimum value of peak-to-peak input ripple voltage (ΔVIN) to be
maintained then the following equation may be used.
(11)
If ΔVIN is 200 mV or 1.66% of VIN for a 12-V input to 3.3-V output application and fSW = 350 kHz then:
(12)
Additional bulk capacitance with higher ESR may be required to damp any resonant effects of the input
capacitance and parasitic inductance of the incoming supply lines. The LMZ23608 typical applications schematic
and evaluation board include a 150-μF 50-V aluminum capacitor for this function. There are many situations
where this capacitor is not necessary.
8.2.2.8 Discontinuous Conduction and Continuous Conduction Modes Selection
The approximate formula for determining the DCM/CCM boundary is as follows:
(13)
The inductor internal to the module is 2.2 μH. This value was chosen as a good balance between low and high
input voltage applications. The main parameter affected by the inductor is the amplitude of the inductor ripple
current (ΔiL). ΔiLcan be calculated with:
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0 1002003004005006007008009001000
0
10
20
30
40
50
AMPLITUDE (dBV/m)
FREQUENCY (MHz)
Horizontal Peak
Vertical Peak
Class B Limit
Class A Limit
0 1 2 3 4 5 6 7 8
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
OUTPUT CURRENT (A)
24 Vin
20 40 60 80 100 120
0
2
4
6
8
10
MAXIMUM OUTPUT CURRENT (A)
TEMPERATURE (C)
JA = 9.9 °C/W
JA = 6.8 °C/W
JA = 5.2 °C/W
LMZ23608
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SNVS708G –MARCH 2011–REVISED AUGUST 2015
where
• VIN is the maximum input voltage
• and fSW is typically 359 kHz. (14)
If the output current IOUT is determined by assuming that IOUT = IL, the higher and lower peak of ΔiLcan be
determined.
8.2.3 Application Curves
VIN = 24 V, VOUT = 3.3 V VIN = 24 V, VOUT = 3.3 V
Figure 53. Efficiency Figure 54. Thermal Derating Curve
VIN = 24 V, VOUT = 5 V,
IOUT = 8 A
Figure 55. Radiated EMI (EN 55022)
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9 Power Supply Recommendations
The LMZ23608 device is designed to operate from an input voltage supply range between 6 V and 36 V. This
input supply must be well regulated and able to withstand maximum input current and maintain a stable voltage.
The resistance of the input supply rail must be low enough that an input current transient does not cause a high
enough drop at the LMZ23608 supply voltage that can cause a false UVLO fault triggering and system reset. If
the input supply is more than a few inches from the LMZ23608, additional bulk capacitance may be required in
addition to the ceramic bypass capacitors. The amount of bulk capacitance is not critical, but a 47-μF or 100-μF
electrolytic capacitor is a typical choice.
10 Layout
10.1 Layout Guidelines
PCB layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance of a
DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce and resistive voltage drop in
the traces. These can send erroneous signals to the DC-DC converter resulting in poor regulation or instability.
Good layout can be implemented by following a few simple design rules. A good layout example is shown in
Figure 59.
1. Minimize area of switched current loops.
From an EMI reduction standpoint, it is imperative to minimize the high di/dt paths during PCB layout as
shown in the figure above. The high current loops that do not overlap have high di/dt content that will cause
observable high frequency noise on the output pin if the input capacitor (CIN) is placed at a distance away
from the LMZ23608. Therefore place CIN as close as possible to the LMZ23608 VIN and PGND exposed
pad. This will minimize the high di/dt area and reduce radiated EMI. Additionally, grounding for both the input
and output capacitor must consist of a localized top side plane that connects to the PGND exposed pad
(EP).
2. Have a single point ground.
The ground connections for the feedback, soft-start, and enable components must be routed to the AGND
pin of the device. This prevents any switched or load currents from flowing in the analog ground traces. If not
properly handled, poor grounding can result in degraded load regulation or erratic output voltage ripple
behavior. Additionally provide a single point ground connection from pin 4 (AGND) to EP/PGND.
3. Minimize trace length to the FB pin.
Both feedback resistors, RFBT and RFBB must be located close to the FB pin. Since the FB node is high
impedance, maintain the copper area as small as possible. The traces from RFBT, RFBB must be routed away
from the body of the LMZ23608 to minimize possible noise pickup.
4. Make input and output bus connections as wide as possible.
This reduces any voltage drops on the input or output of the converter and maximizes efficiency. To optimize
voltage accuracy at the load, ensure that a separate feedback voltage sense trace is made to the load. Doing
so will correct for voltage drops and provide optimum output accuracy.
5. Provide adequate device heat-sinking.
Use an array of heat-sinking vias to connect the exposed pad to the ground plane on the bottom PCB layer.
If the PCB has multiple copper layers, these thermal vias can also be connected to inner layer heat-
spreading ground planes. For best results use a 10 × 10 via array or larger with a minimum via diameter of 8
mil thermal vias spaced 46.8 mil (1.5 mm). Ensure enough copper area is used for heat-sinking to keep the
junction temperature below 125°C.
24 Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LMZ23608
VIN
SYNC
AGND
EN
AGND
VIN
1 2 3 4 5 6 7
Top View
VIN
COUT
VOUT
CSS
GND
Thermal Vias
FB
CIN
GND
CFF
RFBT
RFBB
GND Plane
EPAD
SH
SS
VOUT
8 9 10 11
VOUT
Clock >
Enable >
VIN
PGND
VIN VOUT
CIN COUT
Loop 1 Loop 2
VOUT
High
di/dt
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
10.2 Layout Examples
Figure 56. Critical Current Loops to Minimize
Figure 57. PCB Layout Guide
Figure 58. Top View of Evaluation PCB
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Links: LMZ23608
500
TCA
Board Area_cm2 8°C x cm2
W
.
TCA <125°C - 50°C
3.9 W - 1.0°C
W< 18.23°C
W
TCA <TJ-MAX ± TA-MAX
PIC_LOSS - TJC
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
Layout Examples (continued)
Figure 59. Bottom View of Evaluation PCB
10.3 Power Dissipation and Thermal Considerations
When calculating module dissipation use the maximum input voltage and the average output current for the
application. Many common operating conditions are provided in the characteristic curves such that less common
applications can be derived through interpolation. In all designs, the junction temperature must be kept below the
rated maximum of 125°C.
For the design case of VIN = 12 V, VOUT = 3.3 V, IOUT = 8 A, and TA-MAX = 50°C, the module must see a thermal
resistance from case to ambient (θCA) of less than:
(15)
Given the typical thermal resistance from junction to case (θJC) to be 1.0°C/W. Use the 85°C power dissipation
curves in the Typical Characteristics section to estimate the PIC-LOSS for the application being designed. In this
application it is 3.9 W.
(16)
To reach θCA = 18.23, the PCB is required to dissipate heat effectively. With no airflow and no external heat-sink,
a good estimate of the required board area covered by 2-oz. copper on both the top and bottom metal layers is:
(17)
As a result, approximately 27.42 square cm of 2-oz. copper on top and bottom layers is the minimum required
area for the example PCB design. This is 5.23 × 5.23 cm (2.06 × 2.06 in) square. The PCB copper heat sink
must be connected to the exposed pad. For best performance, use approximately 100, 8 mil thermal vias spaced
59 mil (1.5 mm) apart connect the top copper to the bottom copper.
26 Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LMZ23608
TJA <TJ-MAX - TA-MAX
PIC_LOSS
TJA <(125 - 50) °C
3.9 W < 19.23°C
W
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
Power Dissipation and Thermal Considerations (continued)
Another way to estimate the temperature rise of a design is using θJA. An estimate of θJA for varying heat sinking
copper areas and airflows can be found in the typical applications curves. If our design required the same
operating conditions as before but had 225 LFPM of airflow. We locate the required θJA of
(18)
On the θJA vs copper heatsinking curve, the copper area required for this application is now only 1 square
inches. The airflow reduced the required heat sinking area by a factor of four.
To reduce the heat sinking copper area further, this package is compatable with D3-PAK surface mount heat
sinks.
For an example of a high thermal performance PCB layout for SIMPLE SWITCHER power modules, refer to AN-
2093 SNVA460, AN-2084 SNVA456, AN-2125 SNVA473, AN-2020 SNVA419 and AN-2026 SNVA424.
10.4 Power Module SMT Guidelines
The recommendations below are for a standard module surface mount assembly
• Land Pattern — Follow the PCB land pattern with either soldermask defined or non-soldermask defined pads
• Stencil Aperture
– For the exposed die attach pad (DAP), adjust the stencil for approximately 80% coverage of the PCB land
pattern
– For all other I/O pads use a 1:1 ratio between the aperture and the land pattern recommendation
• Solder Paste — Use a standard SAC Alloy such as SAC 305, type 3 or higher
• Stencil Thickness — 0.125 to 0.15 mm
• Reflow — Refer to solder paste supplier recommendation and optimized per board size and density
• Refer to Design Summary LMZ1xxx and LMZ2xxx Power Modules Family (SNAA214) for reflow information
• Maximum number of reflows allowed is one
Figure 60. Sample Reflow Profile
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 27
Product Folder Links: LMZ23608
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
Power Module SMT Guidelines (continued)
Table 2. Sample Reflow Profile Table
MAX TEMP REACHED TIME ABOVE REACHED TIME ABOVE REACHED TIME ABOVE REACHED
PROBE (°C) MAX TEMP 235°C 235°C 245°C 245°C 260°C 260°C
1242.5 6.58 0.49 6.39 0.00 – 0.00 –
2242.5 7.10 0.55 6.31 0.00 7.10 0.00 –
3241.0 7.09 0.42 6.44 0.00 – 0.00 –
28 Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LMZ23608
LMZ23608
www.ti.com
SNVS708G –MARCH 2011–REVISED AUGUST 2015
11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.1.2 Development Support
For developmental support, see the following:
WEBENCH Tool, http://www.ti.com/webench
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation, see the following:
• AN-2027 Inverting Application for the LMZ14203 SIMPLE SWITCHER Power Module, (SNVA425)
•Absolute Maximum Ratings for Soldering, (SNOA549)
• AN-2024 LMZ1420x / LMZ1200x Evaluation Board (SNVA422)
• AN-2085 LMZ23605/03, LMZ22005/03 Evaluation Board (SNVA457)
• AN-2054 Evaluation Board for LM10000 - PowerWise AVS System Controller (SNVA437)
• AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419)
• AN-2093 LMZ23610/8/6 and LMZ22010/8/6 Current Sharing Evaluation Board (SNVA460)
• AN-2026 Effect of PCB Design on Thermal Performance of SIMPLE SWITCHER Power Modules (SNVA424)
•Design Summary LMZ1xxx and LMZ2xxx Power Modules Family (SNAA214)
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
SIMPLE SWITCHER is a registered trademark of Texas Insturments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.6 Glossary
SLYZ022 —TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: LMZ23608
LMZ23608
SNVS708G –MARCH 2011–REVISED AUGUST 2015
www.ti.com
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
30 Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LMZ23608
PACKAGE OPTION ADDENDUM
www.ti.com 6-Feb-2020
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LMZ23608TZ/NOPB ACTIVE PFM NDY 11 32 RoHS & Green SN Level-3-245C-168 HR -40 to 85 LMZ23608
LMZ23608TZE/NOPB ACTIVE PFM NDY 11 250 RoHS & Green SN Level-3-245C-168 HR -40 to 85 LMZ23608
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LMZ23608TZE/NOPB PFM NDY 11 250 330.0 32.4 15.45 18.34 6.2 20.0 32.0 Q2
PACKAGE MATERIALS INFORMATION
www.ti.com 27-May-2018
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LMZ23608TZE/NOPB PFM NDY 11 250 367.0 367.0 55.0
PACKAGE MATERIALS INFORMATION
www.ti.com 27-May-2018
Pack Materials-Page 2
MECHANICAL DATA
NDY0011A
www.ti.com
TZA11A (Rev F)
TOP SIDE OF PACKAGE
BOTTOM SIDE OF PACKAGE
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