LM2734
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C1
C2
R1
R2
D1
D2
ON
OFF
Product
Folder
Order
Now
Technical
Documents
Tools &
Software
Support &
Community
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.
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
LM2734 Thin SOT 1-A Load Step-Down DC/DC Regulator
1
1 Features
1 Thin SOT-6 Package
3-V to 20-V Input Voltage Range
0.8-V to 18-V Output Voltage Range
1-A Output Current
550-kHz (LM2734Y) and 1.6-MHz (LM2734X)
Switching Frequencies
300-mNMOS Switch
30-nA Shutdown Current
0.8-V, 2% Internal Voltage Reference
Internal Soft Start
Current-Mode, PWM Operation
Thermal Shutdown
Create a Custom Design Using the LM2734 With
WEBENCH®Power Designer
2 Applications
Local Point-of-Load Regulation
Core Power in HDDs
Set-Top Boxes
Battery-Powered Devices
USB Powered Devices
DSL Modems
Notebook Computers
3 Description
The LM2734 regulator is a monolithic, high-
frequency, PWM step-down DC/DC converter in a 6-
pin Thin SOT package. The device provides all the
active functions to provide local DC/DC conversion
with fast transient response and accurate regulation
in the smallest possible PCB area.
With a minimum of external components and online
design support through WEBENCH, the LM2734
regulator is easy to use. The ability to drive 1-A loads
with an internal 300-mNMOS switch using state-of-
the-art 0.5-µm BiCMOS technology results in the best
power density available. The world-class control
circuitry allows for on-times as low as 13 ns, thus
supporting exceptionally high-frequency conversion
over the entire 3-V to 20-V input operating range
down to the minimum output voltage of 0.8 V.
Switching frequency is internally set to 550 kHz
(LM2734Y) or 1.6 MHz (LM2734X), allowing the use
of extremely small surface-mount inductors and chip
capacitors. Even though the operating frequencies
are very high, efficiencies up to 90% are easy to
achieve. External shutdown is included, featuring an
ultra-low standby current of 30 nA.
The LM2734 regulator uses current-mode control and
internal compensation to provide high-performance
regulation over a wide range of operating conditions.
Additional features include internal soft-start circuitry
to reduce inrush current, pulse-by-pulse current limit,
thermal shutdown, and output overvoltage protection.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LM2734 SOT (6) 2.90 mm × 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Typical Application Circuit Efficiency vs Load Current
VIN =5V,VOUT = 3.3 V
2
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description............................................................. 1
4 Revision History..................................................... 2
5 Pin Configuration and Functions......................... 3
6 Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings.............................................................. 4
6.3 Recommended Operating Conditions....................... 4
6.4 Thermal Information.................................................. 4
6.5 Electrical Characteristics........................................... 5
6.6 Typical Characteristics.............................................. 6
7 Detailed Description.............................................. 8
7.1 Overview................................................................... 8
7.2 Functional Block Diagram......................................... 9
7.3 Feature Description................................................... 9
7.4 Device Functional Modes........................................ 10
8 Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Applications ................................................ 14
9 Power Supply Recommendations...................... 29
10 Layout................................................................... 29
10.1 Layout Guidelines ................................................. 29
10.2 Layout Example .................................................... 30
11 Device and Documentation Support................. 31
11.1 Development Support .......................................... 31
11.2 Receiving Notification of Documentation Updates 31
11.3 Community Resources.......................................... 31
11.4 Third-Party Products Disclaimer ........................... 31
11.5 Trademarks........................................................... 31
11.6 Electrostatic Discharge Caution............................ 31
11.7 Glossary................................................................ 32
12 Mechanical, Packaging, and Orderable
Information........................................................... 32
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision J (December 2014) to Revision K Page
Deleted automotive content and moved to separate data sheet SNVSB80 ......................................................................... 1
Added links for Webench ....................................................................................................................................................... 1
Changed Abs Max FB voltage max. from "-0.3 V" to "3 V".................................................................................................... 4
Changes from Revision I (April 2013) to Revision J Page
Added 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
1
2
3
6
5
4
BOOST
GND
FB
SW
VIN
EN
3
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
5 Pin Configuration and Functions
DDC Package
6-Pin SOT-23-THIN
Top View
Pin Functions
PIN I/O DESCRIPTION
NAME NO.
BOOST 1 I Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is
connected between the BOOST and SW pins.
GND 2 GND Signal and Power ground pin. Place the bottom resistor of the feedback network as close as
possible to this pin for accurate regulation.
FB 3 I Feedback pin. Connect FB to the external resistor divider to set output voltage.
EN 4 I Enable control input. Logic high enables operation. Do not allow this pin to float or be greater
than VIN + 0.3 V.
VIN 5 I Input supply voltage. Connect a bypass capacitor to this pin.
SW 6 O Output switch. Connects to the inductor, catch diode, and bootstrap capacitor.
4
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
(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, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature (unless otherwise noted)(1)(2)
MIN MAX UNIT
VIN –0.5 24 V
SW voltage –0.5 24 V
Boost voltage –0.5 30 V
Boost to SW voltage –0.5 6 V
FB voltage –0.5 3 V
EN voltage –0.5 VIN + 0.3 V
Junction temperature 150 °C
Soldering information reflow peak pkg. temp.(15s) 260 °C
Storage temperature, Tstg –65 150 °C
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.2 ESD Ratings VALUE UNIT
VESD Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS001(1) ±2000 V
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) MIN NOM MAX UNIT
VIN 3 20 V
SW voltage -0.5 20 V
Boost voltage -0.5 25 V
Boost to SW voltage 1.6 5.5 V
Junction temperature 40 125 °C
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
6.4 Thermal Information
THERMAL METRIC(1) LM2734
UNITDDC (SOT-23-THIN)
6 PINS
RθJA Junction-to-ambient thermal resistance 158.1 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 46.5 °C/W
RθJB Junction-to-board thermal resistance 29.5 °C/W
ψJT Junction-to-top characterization parameter 0.8 °C/W
ψJB Junction-to-board characterization parameter 29.2 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a °C/W
5
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
(1) Specified to Average Outgoing Quality Level (AOQL).
(2) Typicals represent the most likely parametric norm.
6.5 Electrical Characteristics
VIN = 5V, VBOOST - VSW = 5V unless otherwise specified. Datasheet min/max specification limits are ensured by design, test, or
statistical analysis.
PARAMETER TEST CONDITIONS TJ= 25°C TJ= -40°C to 125°C UNIT
MIN(1) TYP(2) MAX(1) MIN TYP MAX
VFB Feedback Voltage 0.800 0.784 0.816 V
ΔVFB/Δ
VIN Feedback Voltage Line
Regulation VIN = 3V to 20V 0.01 % / V
IFB Feedback Input Bias
Current Sink/Source 10 250 nA
UVLO Undervoltage Lockout VIN Rising 2.74 2.90 VUndervoltage Lockout VIN Falling 2.3 2
UVLO Hysteresis 0.44 0.30 0.62
FSW Switching Frequency LM2734X 1.6 1.2 1.9 MHz
LM2734Y 0.55 0.40 0.66
DMAX Maximum Duty Cycle LM2734X 92 85%
LM2734Y 96 90%
DMIN Minimum Duty Cycle LM2734X 2%
LM2734Y 1%
RDS(ON) Switch ON Resistance VBOOST - VSW = 3V 300 600 m
ICL Switch Current Limit VBOOST - VSW = 3V 1.7 1.2 2.5 A
IQ
Quiescent Current Switching 1.5 2.5 mA
Quiescent Current
(shutdown) VEN = 0V 30 nA
IBOOST Boost Pin Current
LM2734X (50% Duty
Cycle) 2.5 3.5 mA
LM2734Y (50% Duty
Cycle) 1.0 1.8
VEN_TH
Shutdown Threshold
Voltage VEN Falling 0.4 V
Enable Threshold
Voltage VEN Rising 1.8
IEN Enable Pin Current Sink/Source 10 nA
ISW Switch Leakage 40 nA
6
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
6.6 Typical Characteristics
All curves taken at VIN = 5 V, VBOOST VSW = 5 V and TA= 25°C, unless specified otherwise.
Figure 1. Oscillator Frequency vs Temperature - L1 = 4.7 µH Figure 2. Oscillator Frequency vs Temperature - L1 = 10 μH
Figure 3. Current Limit vs Temperature Figure 4. Current Limit vs Temperature
VIN = 20 V
Figure 5. VFB vs Temperature Figure 6. RDSON vs Temperature
7
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
Typical Characteristics (continued)
All curves taken at VIN = 5 V, VBOOST VSW = 5 V and TA= 25°C, unless specified otherwise.
Figure 7. IQSwitching vs Temperature Figure 8. Line Regulation - L1 = 4.7 µH
VOUT = 1.5 V, IOUT = 500 mA
Figure 9. Line Regulation - L1 = 10 μH
VOUT = 1.5 V, IOUT = 500 mA Figure 10. Line Regulation - L1 = 4.7 µH
VOUT = 3.3 V, IOUT = 500 mA
Figure 11. Line Regulation - L1 = 10 μH
VOUT = 3.3 V, IOUT = 500 mA
0
0
VIN
VD
TON
t
t
Inductor
Current
D = TON/TSW
VSW
TOFF
TSW
IL
IPK
SW
Voltage
8
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
7 Detailed Description
7.1 Overview
The LM2734 device is a constant frequency PWM buck regulator IC that delivers a 1-A load current. The
regulator has a preset switching frequency of either 550 kHz (LM2734Y) or 1.6 MHz (LM2734X). These high
frequencies allow the LM2734 device to operate with small surface-mount capacitors and inductors, resulting in
DC/DC converters that require a minimum amount of board space. The LM2734 device is internally
compensated, so it is simple to use, and requires few external components. The LM2734 device uses current-
mode control to regulate the output voltage.
The following operating description of theLM2734 device will refer to the Simplified Block Diagram () and to the
waveforms in Figure 12. The LM2734 device supplies a regulated output voltage by switching the internal NMOS
control switch at constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the
reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the
internal NMOS control switch. During this on-time, the SW pin voltage (VSW) swings up to approximately VIN, and
the inductor current (IL) increases with a linear slope. ILis measured by the current-sense amplifier, which
generates an output proportional to the switch current. The sense signal is summed with the regulator’s
corrective ramp and compared to the error amplifier’s output, which is proportional to the difference between the
feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the
next switching cycle begins. During the switch off-time, inductor current discharges through Schottky diode D1,
which forces the SW pin to swing below ground by the forward voltage (VD) of the catch diode. The regulator
loop adjusts the duty cycle (D) to maintain a constant output voltage.
Figure 12. LM2734 Waveforms of SW Pin Voltage and Inductor Current
L
R
1
R
2
D
1
D2
BOOST
Output
Control
Logic
Current
Limit
Thermal
Shutdown
Under
Voltage
Lockout
Corrective Ramp
Reset
Pulse
PWM
Comparator
Current-Sense Amplifier RSENSE
+
+
Internal
Regulator
and
Enable
Circuit
Oscillator
Driver 0.3:
Switch
Internal
Compensation
SW
EN
FB
GND
Error Amplifier -
+VREF
0.8V
COUT
ON
OFF
VBOOST
IL
VSW
+
-
CBOOST
VOUT
CIN
VIN
VIN
ISENSE
+
-
+
-
+
-0.88V
-
+
OVP
Comparator
Error
Signal
9
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Output Overvoltage Protection
The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal
reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control
switch is turned off, which allows the output voltage to decrease toward regulation.
7.3.2 Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the LM2734 from operating until the input voltage exceeds 2.74 V
(typical).
The UVLO threshold has approximately 440 mV of hysteresis, so the part will operate until VIN drops below 2.3 V
(typical). Hysteresis prevents the part from turning off during power up if VIN is nonmonotonic.
7.3.3 Current Limit
The LM2734 uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a
current limit comparator detects if the output switch current exceeds 1.7 A (typical), and turns off the switch until
the next switching cycle begins.
7.3.4 Thermal Shutdown
Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature
exceeds 165°C. After thermal shutdown occurs, the output switch does not turn on until the junction temperature
drops to approximately 150°C.
10
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
7.4 Device Functional Modes
7.4.1 Enable Pin / Shutdown Mode
The LM2734 has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is applied
to EN, the part is in shutdown mode and its quiescent current drops to typically 30 nA. Switch leakage adds
another 40 nA from the input supply. The voltage at this pin must never exceed VIN + 0.3 V.
7.4.2 Soft Start
This function forces VOUT to increase at a controlled rate during start up. During soft start, the error amplifier’s
reference voltage ramps from 0 V to its nominal value of 0.8 V in approximately 200 µs. This forces the regulator
output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. Under some
circumstances at start-up, an output voltage overshoot may still be observed. This may be due to a large output
load applied during start-up. Large amounts of output external capacitance can also increase output voltage
overshoot. A simple solution is to add a feed forward capacitor with a value between 470 pf and 1000 pf across
the top feedback resistor (R1). See Figure 23 for further detail.
11
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
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
8.1.1 Boost Function
Capacitor CBOOST and diode D2 in Figure 13 are used to generate a voltage VBOOST. VBOOST - VSW is the gate
drive voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its on-time,
VBOOST needs to be at least 1.6 V greater than VSW. Although the LM2734 device will operate with this minimum
voltage, it may not have sufficient gate drive to supply large values of output current. Therefore, it is
recommended that VBOOST be greater than 2.5 V above VSW for best efficiency. VBOOST VSW should not exceed
the maximum operating limit of 5.5 V.
5.5 V > VBOOST VSW > 2.5 V for best performance.
Figure 13. VOUT Charges CBOOST
When the LM2734 device starts up, internal circuitry from the BOOST pin supplies a maximum of 20 mA to
CBOOST. This current charges CBOOST to a voltage sufficient to turn the switch on. The BOOST pin continues to
source current to CBOOST until the voltage at the feedback pin is greater than 0.76 V.
There are various methods to derive VBOOST:
1. From the input voltage (VIN)
2. From the output voltage (VOUT)
3. From an external distributed voltage rail (VEXT)
4. From a shunt or series Zener diode
In the simplified block diagram of Functional Block Diagram, capacitor CBOOST and diode D2 supply the gate-
drive current for the NMOS switch. Capacitor CBOOST is charged via diode D2 by VIN. During a normal switching
cycle, when the internal NMOS control switch is off (TOFF) (refer to Figure 12), VBOOST equals VIN minus the
forward voltage of D2 (VFD2), during which the current in the inductor (L) forward biases the Schottky diode D1
(VFD1). Therefore, the voltage stored across CBOOST is:
VBOOST - VSW = VIN - VFD2 + VFD1 (1)
When the NMOS switch turns on (TON), the switch pin rises to:
VSW = VIN (RDSON × IL), (2)
forcing VBOOST to rise thus reverse biasing D2. The voltage at VBOOST is then:
VBOOST = 2 VIN (RDSON × IL) VFD2 + VFD1 (3)
which is approximately:
2VIN 0.4 V (4)
LM2734
VIN BOOST
SW
GND
CBOOST
L
D1
D2
D3
CIN
VIN
COUT
VOUT
VBOOST
12
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
Application Information (continued)
for many applications. Thus the gate-drive voltage of the NMOS switch is approximately:
VIN 0.2 V (5)
An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 13. The output
voltage should be from 2.5 V and 5.5 V, so that proper gate voltage will be applied to the internal switch. In this
circuit, CBOOST provides a gate drive voltage that is slightly less than VOUT.
In applications where both VIN and VOUT are greater than 5.5 V, or less than 3 V, CBOOST cannot be charged
directly from these voltages. If VIN to VOUT are greater than 5.5 V, CBOOST can be charged from VIN or VOUT minus
a Zener voltage by placing a Zener diode D3 in series with D2, as shown in Figure 14. When using a series
Zener diode from the input, ensure that the regulation of the input supply does not create a voltage that falls
outside the recommended VBOOST voltage.
(VINMAX VD3) < 5.5 V (6)
(VINMIN VD3) > 1.6 V (7)
Figure 14. Zener Reduces Boost Voltage from VIN
An alternative method is to place the Zener diode D3 in a shunt configuration as shown in Figure 15. A small 350
mW to 500 mW 5.1-V Zener diode in a SOT or SOD package can be used for this purpose. A small ceramic
capacitor such as a 6.3 V, 0.1-µF capacitor (C4) should be placed in parallel with the Zener diode. When the
internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The
0.1-µF parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time.
Resistor R3 should be chosen to provide enough RMS current to the Zener diode (D3) and to the BOOST pin. A
recommended choice for the Zener current (IZENER) is 1 mA. The current IBOOST into the BOOST pin supplies the
gate current of the NMOS control switch and varies typically according to the following formula for the X version:
IBOOST = 0.56 × (D + 0.54) × (VZENER VD2) mA (8)
IBOOST can be calculated for the Y version using the following:
IBOOST = 0.22 × (D + 0.54) × (VZENER VD2) µA (9)
where D is the duty cycle, VZENER and VD2 are in volts, and IBOOST is in milliamps. VZENER is the voltage applied to
the anode of the boost diode (D2), and VD2 is the average forward voltage across D2. Note that this formula for
IBOOST gives typical current. For the worst case IBOOST, increase the current by 40%. In that case, the worst case
boost current will be:
IBOOST-MAX = 1.4 × IBOOST (10)
R3 will then be given by:
R3 = (VIN VZENER) / (1.4 × IBOOST + IZENER) (11)
For example, using the X-version let VIN = 10 V, VZENER =5V,VD2 = 0.7 V, IZENER = 1 mA, and duty cycle D =
50%. Then:
IBOOST = 0.56 × (0.5 + 0.54) × (5 - 0.7) mA = 2.5 mA (12)
R3 = (10 V 5 V) / (1.4 × 2.5 mA + 1 mA) = 1.11 k(13)
LM2734
VIN BOOST
SW
GND
L
D1
D2
D3
R3
C4
VBOOST
CBOOST
VZ
VIN
CIN
VOUT
COUT
13
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
Application Information (continued)
Figure 15. Boost Voltage Supplied from the Shunt Zener on VIN
LM2734
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
C1 R3
14
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
8.2 Typical Applications
8.2.1 LM2734X (1.6 MHz) VBOOST Derived from VIN 5V to 1.5 V/1 A
Figure 16. LM2734X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5-V/1-A Schematic
8.2.1.1 Design Requirements
Derive charge for VBOOST from the input supply (VIN ). VBOOST VSW should not exceed the maximum operating
limit of 5.5V.
8.2.1.2 Detailed Design Procedure
Table 1. Bill of Materials for Figure 16
PART ID PART VALUE MANUFACTURER PART NUMBER
U1 1-A Buck Regulator Texas Instruments LM2734X
C1, Input Cap 10 µF, 6.3V, X5R TDK C3216X5ROJ106M
C2, Output Cap 10 µF, 6.3V, X5R TDK C3216X5ROJ106M
C3, Boost Cap 0.01 uF, 16V, X7R TDK C1005X7R1C103K
D1, Catch Diode 0.3 VFSchottky 1 A, 10 VR ON Semi MBRM110L
D2, Boost Diode 1VF@ 50-mA Diode Diodes, Inc. 1N4148W
L1 4.7µH, 1.7A, TDK VLCF4020T- 4R7N1R2
R1 8.87 k, 1% Vishay CRCW06038871F
R2 10.2 k, 1% Vishay CRCW06031022F
R3 100 k, 1% Vishay CRCW06031003F
8.2.1.2.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM2734 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
Run electrical simulations to see important waveforms and circuit performance
Run thermal simulations to understand board thermal performance
Export customized schematic and layout into popular CAD formats
Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
L = VO + VD
IO x r x fSx (1-D)
r = 'iL
lO
D = VO + VD
VIN + VD - VSW
D = VO
VIN
15
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
8.2.1.2.2 Inductor Selection
The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN):
(14)
The catch diode (D1) forward voltage drop and the voltage drop across the internal NMOS must be included to
calculate a more accurate duty cycle. Calculate D by using the following formula:
(15)
VSW can be approximated by:
VSW = IOx RDS(ON) (16)
The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower VD
is, the higher the operating efficiency of the converter.
The inductor value determines the output ripple current. Lower inductor values decrease the size of the inductor,
but increase the output ripple current. An increase in the inductor value will decrease the output ripple current.
The ratio of ripple current (ΔiL) to output current (IO) is optimized when it is set between 0.3 and 0.4 at 1 A. The
ratio r is defined as:
(17)
One must also ensure that the minimum current limit (1.2 A) is not exceeded, so the peak current in the inductor
must be calculated. The peak current (ILPK) in the inductor is calculated as shown in Equation 18:
ILPK = IO+ΔIL/2 (18)
If r = 0.5 at an output of 1 A, the peak current in the inductor will be 1.25 A. The minimum specified current limit
over all operating conditions is 1.2 A. One can either reduce r to 0.4 resulting in a 1.2-A peak current, or make
the engineering judgement that 50 mA over is safe enough with a 1.7-A typical current limit and 6 sigma limits.
When the designed maximum output current is reduced, the ratio r can be increased. At a current of 0.1 A, r can
be made as high as 0.9. The ripple ratio can be increased at lighter loads because the net ripple is actually quite
low, and if r remains constant the inductor value can be made quite large. An equation empirically developed for
the maximum ripple ratio at any current less than 2 A is:
r = 0.387 x IOUT-0.3667 (19)
Note that this is just a guideline.
The LM2734 operates at frequencies allowing the use of ceramic output capacitors without compromising
transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple.
See Output Capacitor for more details on calculating output voltage ripple.
Now that the ripple current or ripple ratio is determined, the inductance is calculated as shown in Equation 20:
where
fsis the switching frequency
IOis the output current. (20)
When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating.
Inductor saturation will result in a sudden reduction in inductance and prevent the regulator from operating
correctly. Because of the speed of the internal current limit, it necessary to specify the peak current of the
inductor only for the required maximum output current. For example, if the designed maximum output current is
0.5 A and the peak current is 0.7 A, then the inductor should be specified with a saturation current limit of >0.7 A.
IRMS-OUT = IO x r
12
'VO = 'iL x (RESR + 1
8 x fS x CO)
IRMS-IN = IO x D x r2
12
1-D +
16
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
There is no need to specify the saturation or peak current of the inductor at the 1.7-A typical switch current limit.
The difference in inductor size is a factor of 5. Because of the operating frequency of the LM2734, ferrite based
inductors are preferred to minimize core losses. This presents little restriction because the variety of ferrite based
inductors is huge. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For
recommended inductors see example circuits.
8.2.1.2.3 Input Capacitor
An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The
primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and ESL (Equivalent
Series Inductance). The recommended input capacitance is 10 µF, although 4.7 µF is sufficient for input voltages
below 6 V. The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any
recommended deratings and also verify if there is any significant change in capacitance at the operating input
voltage and the operating temperature. The input capacitor maximum RMS input current rating (IRMS-IN) must be
greater than:
(21)
From Equation 21 from the above equation that maximum RMS capacitor current occurs when D = 0.5. Always
calculate the RMS at the point where the duty cycle, D, is closest to 0.5. The ESL of an input capacitor is usually
determined by the effective cross sectional area of the current path. A large leaded capacitor will have high ESL
and a 0805 ceramic chip capacitor will have very low ESL. At the operating frequencies of the LM2734 device,
certain capacitors may have an ESL so large that the resulting impedance (2πfL) will be higher than that required
to provide stable operation. As a result, surface-mount capacitors are strongly recommended. Sanyo POSCAP,
Tantalum or Niobium, Panasonic SP or Cornell Dubilier ESR, and multilayer ceramic capacitors (MLCC) are all
good choices for both input and output capacitors and have very low ESL. For MLCCs it is recommended to use
X7R or X5R dielectrics. Consult the capacitor manufacturer data sheet to see how rated capacitance varies over
operating conditions.
8.2.1.2.4 Output Capacitor
The output capacitor is selected based upon the desired output ripple and transient response. The initial current
of a load transient is provided mainly by the output capacitor. The output ripple of the converter is:
(22)
When using MLCCs, the ESR is typically so low that the capacitive ripple may dominate. When this occurs, the
output ripple will be approximately sinusoidal and 90° phase shifted from the switching action. Given the
availability and quality of MLCCs and the expected output voltage of designs using the LM2734 device, there is
really no need to review any other capacitor technologies. Another benefit of ceramic capacitors is their ability to
bypass high frequency noise. A certain amount of switching edge noise will couple through parasitic
capacitances in the inductor to the output. A ceramic capacitor will bypass this noise while a tantalum will not.
Because the output capacitor is one of the two external components that control the stability of the regulator
control loop, most applications will require a minimum at 10 µF of output capacitance. Capacitance can be
increased significantly with little detriment to the regulator stability. Like the input capacitor, recommended
multilayer ceramic capacitors are X7R or X5R. Again, verify actual capacitance at the desired operating voltage
and temperature.
Check the RMS current rating of the capacitor. The RMS current rating of the capacitor chosen must also meet
the following condition:
(23)
8.2.1.2.5 Catch Diode
The catch diode (D1) conducts during the switch off-time. A Schottky diode is recommended for its fast switching
times and low forward voltage drop. The catch diode should be chosen so that its current rating is greater than:
ID1 = IOx (1-D) (24)
17
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin.
To improve efficiency choose a Schottky diode with a low forward voltage drop.
8.2.1.2.6 Boost Diode
A standard diode such as the 1N4148 type is recommended. For VBOOST circuits derived from voltages less than
3.3 V, a small-signal Schottky diode is recommended for greater efficiency. A good choice is the BAT54 small
signal diode.
8.2.1.2.7 Boost Capacitor
A ceramic 0.01-µF capacitor with a voltage rating of at least 16 V is sufficient. The X7R and X5R MLCCs provide
the best performance.
R1 =VO- 1
VREF x R2
18
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
8.2.1.2.8 Output Voltage
The output voltage is set using the following equation where R2 is connected between the FB pin and GND, and
R1 is connected between VOand the FB pin. A good value for R2 is 10 k.
(25)
8.2.1.3 Application Curves
Figure 17. Efficiency vs Load Current - L1 = 4.7 µH VOUT =
5 V Figure 18. Efficiency vs Load Current - L1 = 10 μH VOUT = 5
V
Figure 19. Efficiency vs Load Current - L1 = 4.7 µH VOUT =
3.3 V Figure 20. Efficiency vs Load Current - L1 = 10 μH VOUT =
3.3 V
19
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
Figure 21. Efficiency vs Load Current - L1 = 4.7 µH VOUT =
1.5 V Figure 22. Efficiency vs Load Current - L1 = 10 μH VOUT =
1.5 V
LM2734
VIN
EN
BOOST
SW
FB
GND
C3
R1
R2
D1
D2
VOUT
CFF
12V
VIN
3.3V
L1
C1
ON
OFF
R3
C2
20
LM2734
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
www.ti.com
Product Folder Links: LM2734
Submit Documentation Feedback Copyright © 2004–2018, Texas Instruments Incorporated
8.2.2 LM2734X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V /1 A
Figure 23. LM2734X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V /1-A Schematic
8.2.2.1 Design Requirements
Derive charge for VBOOST from the output voltage, (VOUT). The output voltage should be between 2.5 V and 5.5 V.
8.2.2.2 Detailed Design Procedure
See Detailed Design Procedure.
Table 2. Bill of Materials for Figure 23
PART ID PART VALUE MANUFACTURER PART NUMBER
U1 1-A Buck Regulator Texas Instruments LM2734X
C1, Input Cap 10 µF, 25 V, X7R TDK C3225X7R1E106M
C2, Output Cap 22 µF, 6.3 V, X5R TDK C3216X5ROJ226M
C3, Boost Cap 0.01 µF, 16 V, X7R TDK C1005X7R1C103K
CFF 1000 pF 25 V TDK C0603X5R1E102K
D1, Catch Diode 0.34 VFSchottky 1 A, 30 VR Vishay SS1P3L
D2, Boost Diode 1 VF@ 50-mA Diode Diodes, Inc. 1N4148W
L1 4.7µH, 1.7 A TDK VLCF4020T- 4R7N1R2
R1 31.6 k, 1% Vishay CRCW06033162F
R2 10 k, 1% Vishay CRCW06031002F
R3 100 k, 1% Vishay CRCW06031003F
8.2.2.3 Application Curves
See Application Curves.
LM2734
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
D3
C4
R4
C1 R3
21
LM2734
www.ti.com
SNVS288K SEPTEMBER 2004REVISED SEPTEMBER 2018
Product Folder Links: LM2734
Submit Documentation FeedbackCopyright © 2004–2018, Texas Instruments Incorporated
8.2.3 LM2734X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V /1 A
Figure 24. LM2734X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V /1-A Schematic
8.2.3.1 Design Requirements
An alternative method when VIN is greater than 5.5 V is to place the zener diode D3 in a shunt configuration. A
small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic
capacitor such as a 6.3 V, 0.1 μF capacitor (C4) should be placed in parallel with the zener diode. When the
internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The
0.1 μF parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time.
8.2.3.2 Detailed Design Procedure
See Detailed Design Procedure.
Table 3. Bill of Materials for Figure 24
PART ID PART VALUE MANUFACTURER PART NUMBER
U1 1-A Buck Regulator Texas Instruments LM2734X
C1, Input Cap 10 µF, 25 V, X7R TDK C3225X7R1E106M
C2, Output Cap 22 µF, 6.3 V, X5R TDK C3216X5ROJ226M
C3, Boost Cap 0.01 µF, 16 V, X7R TDK C1005X7R1C103K
C4, Shunt Cap 0.1 µF, 6.3 V, X5R TDK C1005X5R0J104K
D1, Catch Diode 0.4 VFSchottky 1 A, 30 VR Vishay SS1P3L
D2, Boost Diode 1 VF@ 50-mA Diode Diodes, Inc. 1N4148W
D3, Zener Diode 5.1 V 250 Mw SOT Vishay BZX84C5V1
L1 6.8 µH, 1.6 A, TDK SLF7032T-6R8M1R6
R1 8.87 k, 1% Vishay CRCW06038871F
R2 10.2 k, 1% Vishay CRCW06031022F
R3 100 k, 1% Vishay CRCW06031003F
R4 4.12 k, 1% Vishay CRCW06034121F
8.2.3.3 Application Curves
See Application Curves.