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September 2015
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0
FAN23SV06AMPX / FAN23SV06PAMPX— 6 A Synchronous Buck Regulator
FAN23SV06AMPX / FAN23SV06PAMPX
6 A Synchronous Buck Regulator
Features
VIN Range: 7 V to 18 V Using Internal Linear
Regulator for Bias
VIN Range: 4.5 V to 5.5 V with VIN/PVIN/PVCC
Connected to Bypass Internal Regulator
High Efficiency: Over 96% Peak
Continuous Output Current: 6 A
Accurate Enable Facilitates VIN UVLO Functionality
PFM Mode for Light-Load Efficiency
Forced PWM Mode Option (FAN23SV06PA)
Excellent Line and Load Transient Response
Precision Reference: ±1% Over Temperature
Output Voltage Range: 0.6 to 5.5 V
Programmable Frequency: 200 kHz to 1.5 MHz
Programmable Soft-Start
Low Shutdown Current
Adjustable Sourcing Current Limit
Internal Boot Diode
Thermal Shutdown
Halogen and Lead Free, RoHS Compliant
Applications
Servers and Desktop Computers
NVDC Notebooks, Netbooks
Game Consoles
Telecommunications
Storage
Description
The FAN23SV06A/FAN23SV06PA is a highly efficient
synchronous buck regulator. The regulator is capable of
operating with an input range from 7 V to 18 V and
supporting 6 A continuous load currents. The device can
operate from a 5 V rail (±10%) if VIN, PVIN, and PVCC are
connected together to bypass the internal linear
regulator.
These devices utilize Fairchild’s constant on-time
control architecture to provide excellent transient
response and to maintain a relatively constant switching
frequency. The FAN23SV06A utilizes Pulse Frequency
Modulation (PFM) mode to maximize light-load
efficiency by reducing switching frequency when the
inductor is operating in discontinuous conduction mode
at light loads. The FAN23SV06PA with forced Pulse
Width Modulation (PWM) mode is available for
applications that require a relatively constant switching
frequency across the full load range.
Switching frequency and over-current protection can
be programmed to provide a flexible solution for
various applications. Output over-voltage, under-
voltage, over-current, and thermal shutdown protections
help prevent damage to the device during fault
conditions. After thermal shutdown is activated, a
hysteresis feature restarts the device when normal
operating temperature is reached.
Ordering Information
Part Number
Configuration
Operating
Temperature Range
Output
Current (A)
Package
FAN23SV06AMPX
PFM with Ultrasonic Mode
-40 to 125°C
6
34-Lead, PQFN,
5.5 mm x 5.0 mm
FAN23SV06PAMPX
Forced PWM
-40 to 125°C
6
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 2
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Typical Application Diagram
R2
1.5kΩ
C4
0.1µF
C5
100pF
L1
1.2µH
R5 1.50kΩ
C10
2.2µF
C9
0.1µF
R11
10Ω
R9
54.9kΩ
C3
0.1µF
CIN
2x10µF
R3
10kΩ
COUT
4x47µF
VIN = 12V
VOUT = 1.2V
IOUT=0-6A
C7
15nF
R4
10kΩ
PVIN
PGND
SW
PVCC
VCC
EN
ILIM
AGND
FREQ
BOOT
SOFT START
FB
VIN
R7
61.9kΩ
CIN
0.1µF
FAN23SV06A
FAN23SV06PA
Ext
EN
R7, R8 used for Accurate EN
R7, R8 open for Ext EN
PGOOD
VIN = 12V
R8
10kΩ
R6
4.99kΩ
Figure 1. Typical Application with VIN = 12 V
R2
1.5kΩ
C4
0.1µF
C5
100pF
L1
1.2µH
R5 1.50kΩ
C10
2.2µF
C9
0.1µF
R11
10Ω
R9
54.9kΩ
C3
0.1µF
CIN
2x10µF
R3
10kΩ
COUT
4x47µF
VIN = 5V
VOUT = 1.2V
IOUT=0-6A
C7
15nF
R4
10kΩ
PVIN
PGND
SW
PVCC
VCC
EN
ILIM
AGND
FREQ
BOOT
SOFT START
FB
VIN
CIN
0.1µF
FAN23SV06A
FAN23SV06PA
Ext
EN
PGOOD
R6
4.99kΩ
Figure 2. Typical Application with VIN = 5 V
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 3
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
-
Functional Block Diagram
Control
Logic
PVCC
PVCC
VCC
Modulator
VCC
Thermal
Shutdown
2nd Level OVP
Comparator
1st Level OVP
Comparator
Under Voltage
Comparator
FB
Comparator
Current Limit
Comparator
PFM
Comparator
HS Gate
Driver
LS Gate
Driver
VREF
x1.2
x1.1
x0.9
VCC
Linear
Regulator
VCC UVLO
PVCC
SW
PGNDILIM
PGOOD
FREQ
FB
SS
VCC
PVCC
VIN BOOT PVIN
AGND
VCC
EN ENABLE
10µA
10µA
1.26V/1.14V
Figure 3. Block Diagram
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 4
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Pin Configuration
9
34
17
26 18
27
10
8
72 3 6
5
4
16
15
14
13
12
11
192021
22232425
33
28
29
30
31
32
PGND
PGND
PGND
PGND
PVIN
PVIN
SW
SW
SW
SW
SW
SW
AGND
SW
VCC
PVCC
ILIM
FB
NC
NC
NC
SS
EN
FREQ
PGOOD
PVIN
PVIN
PVIN
PVIN
PVIN
AGND
BOOT
SW
VIN
AGND
(P1)
PVIN
(P2)
SW
(P3)
1
PVIN
AGND
PVIN
PVIN
PVIN
PVIN
PVIN
SW
SW
SW
SW
SW
SW
PGND
PGND
PGND
PGND
SW
VCC
PVCC
ILIM
FB
NC
NC
NC
SS
EN
FREQ
PGOOD
AGND
BOOT
SW
VIN
PVIN
1
9
10
27
26
18
17
34
2
38 7 4
5
6
28
29
30
31
32
33
19 20 21 22 23 24 25
11
16
15
14
13
12
Figure 4. Pin Assignments, Bottom View
Figure 5. Pin Assignments, Top View
Pin Definitions
Name
Pad / Pin
Description
PVIN
P2, 5-11
Power input for the power stage
VIN
1
Power input to the linear regulator; used in the modulator for input voltage feed-
forward.
PVCC
25
Power output of the linear regulator; directly supplies power for the low-side gate driver
and boot diode. Can be connected to VIN and PVIN for operation from 5 V rail.
VCC
26
Power supply input for the controller
PGND
18-21
Power ground for the low-side power MOSFET and for the low-side gate driver.
AGND
P1, 4, 23
Analog ground for the analog portions of the IC and for substrate.
SW
P3, 2, 12-17, 22
Switching node; junction between high- and low-side MOSFETs
BOOT
3
Supply for high-side MOSFET gate driver. A capacitor from BOOT to SW supplies the
charge to turn on the N-channel, high-side MOSFET. During the freewheeling interval
(low-side MOSFET on), the high-side capacitor is recharged by an internal diode
connected to PVCC.
ILIM
24
Current limit. A resistor between ILIM and SW sets the current limit threshold.
FB
27
Output voltage feedback to the modulator
EN
29
Enable input to the IC. Pin must be driven logic high to enable, or logic low to disable.
SS
31
Soft-start input to the modulator
FREQ
32
On-time and frequency programming pin. Connect a resistor between FREQ and
AGND to program on-time and switching frequency.
PGOOD
30
Power good; open-drain output indicating VOUT is within set limits.
NC
28, 33-34
Leave pin open or connect to AGND
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 5
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Symbol
Parameter
Conditions
Min.
Max.
Unit
VPVIN
Power Input
Referenced to PGND
-0.3
25.0
V
VIN
Modulator Input
Referenced to AGND
-0.3
25.0
V
VBOOT
Boot Voltage
Referenced to PVCC
-0.3
26.0
V
Referenced to PVCC, <20 ns
-0.3
30.0
V
VSW
SW Voltage to GND
Referenced to PGND, AGND
-1
25
V
Referenced to PGND, AGND < 20 ns
-5
25
V
VBOOT
Boot to SW Voltage
Referenced to SW
-0.3
6.0
V
Boot to PGND
Referenced to PGND
-0.3
30
V
VPVCC
Gate Drive Supply Input
Referenced to PGND, AGND
-0.3
6.0
V
VVCC
Controller Supply Input
Referenced to PGND, AGND
-0.3
6.0
V
VILIM
Current Limit Input
Referenced to AGND
-0.3
6.0
V
VFB
Output Voltage Feedback
Referenced to AGND
-0.3
6.0
V
VEN
Enable Input
Referenced to AGND
-0.3
6.0
V
VSS
Soft Start Input
Referenced to AGND
-0.3
6.0
V
VFREQ
Frequency Input
Referenced to AGND
-0.3
6.0
V
VPGOOD
Power Good Output
Referenced to AGND
-0.3
6.0
V
ESD
Electrostatic Discharge
Human Body Model, JESD22-A114
1000
V
Charged Device Model, JESD22-C101
2500
V
TJ
Junction Temperature
+150
°C
TSTG
Storage Temperature
-55
+150
°C
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
Parameter
Conditions
Min.
Max.
Unit
VPVIN
Power Input
Referenced to PGND
7
18
V
VIN
Modulator Input
Referenced to AGND
7
18
V
TJ
Junction Temperature
-40
+125
°C
ILOAD
Load Current
TA=25°C, No Airflow
9
A
VPVIN,
VIN,
VPVCC
PVIN, VIN, and Gate Drive Supply
Input
VPVIN, VIN, VPVCC Connected for 5 V Rail
Operation and Referenced to PGND, AGND
4.5
5.5
V
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 6
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Thermal Characteristics
The thermal characteristics were evaluated on a 4-layer pcb structure (1 oz/1 oz/1 oz/1 oz) measuring 7 cm x 7 cm).
Symbol
Parameter
Typ.
Unit
JA
Thermal Resistance, Junction-to-Ambient
35
°C/W
ψJC
Thermal Characterization Parameter, Junction-to-Top of Case
2.7
°C/W
ψJPCB
Thermal Characterization Parameter, Junction-to-PCB
2.3
°C/W
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 7
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Electrical Characteristics
Unless otherwise noted; VIN=12 V, VOUT=1.2 V, and TA = TJ = -40 to +125°C (1)
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
Supply Current
IVIN,SD
Shutdown Current
EN=0 V
16
µA
IVIN,Q
Quiescent Current
EN=5 V, Not Switching
1.8
mA
IVIN,GateCharge
Gate Charge Current
EN=5 V, fSW=500 kHz
10
mA
Linear Regulator
VREG
Regulator Output Voltage
4.75
5.00
5.25
V
IREG
Regulator Current Limit(2)
60
mA
Reference, Feedback Comparator
VFB
FB Voltage Threshold
590
596
602
mV
IFB
FB Pin Bias Current
-100
0
100
nA
Modulator
tON
On-Time Accuracy
RFREQ=56.2 k, VIN=10 V,
tON=250 ns, No Load
-20
20
%
tOFF,MIN
Minimum SW Off-Time
320
374
ns
DMIN
Minimum Duty Cycle
FB=1 V
0
%
fMINF
Minimum Frequency Clamp
FAN23SV06A Only
18
25
32
kHz
Soft-Start
ISS
Soft-Start Current
SS=0 V
7
10
13
µA
tON,SSMOD
Soft-Start On-Time Modulation
SS<0.6 V
25
100
%
VSSCLAMP,NOM
Nominal Soft-Start Voltage Clamp
VFB=0.6 V
400
mV
VSSCLAMP,OVL
Soft-Start Voltage Clamp in Overload
Condition
VFB=0.3 V, OC Condition
40
mV
PFM Zero-Crossing Detection Comparator
VOFF
ZCD Offset Voltage
TA=TJ=25°C
-6
0
mV
Current Limit
ILIM
Valley Current Limit Accuracy
TA=TJ =25°C,
IVALLEY=7 A
-10
10
%
KILIM
ILIM Set-Point Scale Factor
233
ILIMTC
Temperature Coefficient
4000
ppm/°C
Enable
VTH+
Rising Threshold
1.11
1.26
1.43
V
VHYST
Hysteresis
122
mV
VTH-
Falling Threshold
1.00
1.14
1.28
V
VENCLAMP
Enable Voltage Clamp
IEN=20 µA
4.3
4.5
V
IENCLAMP
Clamp Current
24
µA
IENLK
Enable Pin Leakage
VEN=1.2 V
100
nA
IENLK
Enable Pin Leakage
VEN=5 V
76
µA
UVLO
VON
VCC Good Threshold Rising
4.4
V
VHYS
Hysteresis Voltage
160
mV
Continued on the following page…
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 8
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Electrical Characteristics (Continued)
Unless otherwise noted; VIN=12 V, VOUT=1.2 V, and TA = TJ = -40 to +125°C (1)
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
Fault Protection
VUVP
PGOOD UV Trip Point
On FB Falling
86
89
92
%
VVOP1
PGOOD OV Trip Point
On FB Rising
108
111
115
%
VOVP2
Second OV Trip Point
On FB Rising; LS=On
118
122
125
%
RPGOOD
PGOOD Pull-Down Resistance
IPGOOD=2 mA
125
Ω
tPG,SSDELAY
PGOOD Soft-Start Delay
0.82
1.42
2.03
ms
IPG,LEAK
PGOOD Leakage Current
1
µA
Thermal Shutdown
TOFF
Thermal Shutdown Trip Point(2)
155
°C
THYS
Hysteresis(2)
15
°C
Internal Bootstrap Diode
VFBOOT
Forward Voltage
IF=10 mA
0.6
V
IR
Reverse Leakage
VR=24 V
1000
µA
Notes:
1. Device is 100% production tested at TA=25°C. Limits over that temperature are guaranteed by design.
2. Guaranteed by design; not production tested.
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 9
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Typical Performance Characteristics
Tested using evaluation board circuit shown in Figure 1 with VIN=12 V, VOUT=1.2 V, fSW=500 kHz, TA=25°C, and
no airflow; unless otherwise specified.
Figure 6. FAN23SV06A Efficiency vs. Load Current
with VIN=12 V and fSW=500 kHz
Figure 7. FAN23SV06A Efficiency vs. Load Current
with VIN=12 V and VOUT=1.2 V
Figure 8. FAN23SV06A Efficiency vs. Load Current
with VIN=12 V
Figure 9. FAN23SV06PA Efficiency vs. Load Current
VIN=12 V and fSW=500 kHz
Figure 10. FAN23SV06PA Efficiency vs. Load Current
with VIN=12 V and VOUT=1.2 V
Figure 11. Case Temperature Rise vs. Load Current on
4 Layer PCB, 1 oz Copper, 7 cm x 7 cm
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10
Efficiency (%)
Load Current (A)
Vo=5V, L=3.3uH
Vo=3.3V, L=2.4uH
Vo=1.2V, L=1.2uH
Vo=1.05, L=1.2uH
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10
Efficiency (%)
Load Current (A)
Fsw=300kHz, L=1.8uH
Fsw=500kHz, L=1.2uH
Fsw=1MHz, L=0.56uH
Fsw=1.5MHz, L=0.4uH
60
65
70
75
80
85
90
95
100
0 2 4 6 8 10
Efficiency (%)
Load Current (A)
Vo=5V, L=3.3uH, 500kHz
Vo=3.3V, L=2.4uH, 500kHz
Vo=1.2V, L=1.8uH, 300kHz
Vo=1.2V, L=1.2uH, 500kHz
Vo=1.2V, L=0.56uH, 1MHz
Vo=1.2V, L=0.4uH, 1.5MHz
50
60
70
80
90
100
0 2 4 6 8 10
Efficiency (%)
Load Current (A)
Vo=5V, L=3.3uH
Vo=3.3V, L=2.4uH
Vo=1.2V, L=1.2uH
Vo=1.05V, L=1.2uH
50
60
70
80
90
100
0 2 4 6 8 10
Efficiency (%)
Load Current (A)
Fsw=300kHz, L=1.8uH
Fsw=500kHz, L=1.2uH
Fsw=1MHz, L=0.56uH
Fsw=1.5MHz, L=0.4uH
0
5
10
15
20
25
30
35
0 5 10
Case Temperature Rise (°C)
Load Current (A)
12Vi/1.2Vo/500kHz
12Vi/1.2Vo/1MHz
12Vi/1.2Vo/1.5MHz
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 10
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Typical Performance Characteristics
Tested using evaluation board circuit shown in Figure 1 with VIN=12 V, VOUT=1.2 V, fSW=500 kHz, TA=25°C, and
no airflow; unless otherwise specified.
Figure 12. Load Regulation
Figure 13. Line Regulation
Figure 14. Startup Waveforms with 0 A Load Current
Figure 15. Startup Waveforms with 6 A Load Current
Figure 16. Shutdown Waveforms with 6 A Load Current
Figure 17. FAN23SV06A Startup Waveforms with
Pre-Bias Voltage on Output
1.180
1.185
1.190
1.195
1.200
1.205
1.210
1.215
1.220
0 1 2 3 4 5 6
Output Voltage (V)
Output Current (A)
1.190
1.195
1.200
1.205
1.210
1.215
1.220
7 9 11 13 15
Output Voltage (V)
Input Voltage (V)
Load=0A
Load = 6A
EN (5V/div)
Soft Start (0.5V/div)
Vout (0.5V/div)
PGOOD (5V/div)
Vin=12V
Iout=0A
Time (500µs/div)
EN (5V/div)
Soft Start (0.5V/div)
Vout (0.5V/div)
PGOOD (5V/div)
Vin=12V
Iout=6A
EN (5V/div)
Soft Start (0.5V/div)
Vout (0.5V/div)
PGOOD (5V/div)
Vin=12V
Iout=6A
EN (5V/div)
Soft Start (0.5V/div)
Vout (0.5V/div)
PGOOD (5V/div)
Vin=12V
Iout=0A
Vout Prebias
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 11
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Typical Performance Characteristics
Tested using evaluation board circuit shown in Figure 1 with VIN=12 V, VOUT=1.2 V, fSW=500 kHz, TA=25°C, and
no airflow; unless otherwise specified.
Figure 18. FAN23SV06A Static Output Ripple at
Light Load
Figure 19. Static Output Ripple at Full Load
Figure 20. FAN23SV06PA Static Output Ripple with
No Load
Figure 21. FAN23SV06A Operation as Load Changes
from 0 A to 2 A
Figure 22. FAN23SV06A Operation as Load Changes
from 2 A to 0 A
Figure 23. FAN23SV06PA Operation as Load Changes
from 0 A to 3 A
Vout (20mV/div)
VSW (5V/div)
Vin=12V
Iout=0.1A
Vout (20mV/div)
VSW (5V/div)
Vin=12V
Iout=6A
Vout (20mV/div)
VSW (5V/div)
Vin=12V
Iout=0.1A
Vout (20mV/div)
Iout (1A/div)
Vin=12V
Vout=1.2V
Vout (20mV/div)
Iout (1A/div) Vin=12V
Vout=1.2V
Vout (20mV/div)
Iout (1A/div)
Vin=12V
Vout=1.2V
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 12
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Typical Performance Characteristics
Tested using evaluation board circuit shown in Figure 1 with VIN=12 V, VOUT=1.2 V, fSW=500 kHz, TA=25°C, and
no airflow; unless otherwise specified.
Figure 24. FAN23SV06PA Operation as Load Changes
from 3 A to 0 A
Figure 25. FAN23SV06PA Load Transient from 0% to
50% Load Current
Figure 26. FAN23SV06A Load Transient from 0% to
50% Load Current
Figure 27. Load Transient from 50% to 100%
Load Current
Figure 28. Over-Current Protection with Heavy Load
Figure 29. Over-Voltage Protection Level 1 and 2
Vout (20mV/div)
Iout (2A/div)
Vin=12V, Vout=1.2V
Iout from 0A to 3A, 2.5A/us
Vout (20mV/div)
Iout (2A/div)
Vin=12V, Vout=1.2V
Iout from 0A to 3A, 2.5A/us
Vout (20mV/div)
Iout (2A/div)
Vin=12V, Vout=1.2V
Iout from 0A to 3A, 2.5A/us
PGOOD (5V/div)
Vout (1V/div)
Soft Start (1V/div)
IL (5A/div) Iout=0A then short output
PGOOD indicates UVP
with Vout falling in OCP
Vout (1V/div)
Vfb (0.5V/div)
PGOOD (5V/div)
Vsw (10V/div)
Level 1
Level 2
Pull Vout to 3.8V
through 3Ω resistor
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 13
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Operation Description
The FAN23SV06A uses a constant on-time modulation
architecture with a VIN feed-forward input to
accommodate a wide VIN range. This method provides
fixed switching frequency (fSW) operation when the
inductor operates in Continuous Conduction Mode
(CCM) and variable frequency when operating in Pulse
Frequency Mode (PFM) at light loads. Additional
benefits include excellent line and load transient
response, cycle-by-cycle current limiting, and no loop
compensation requirement.
At the beginning of each cycle, FAN23SV06A turns on
the high-side MOSFET (HS) for a fixed duration (tON). At
the end of tON, HS turns off for a duration (tOFF)
determined by the operating conditions. Once the FB
voltage (VFB) falls below the reference voltage (VREF), a
new switching cycle begins.
The modulator provides a minimum off-time (tOFF-MIN) of
320 ns to provide a guaranteed interval for low-side
MOSFET (LS) current sensing and PFM operation. tOFF-
MIN is also used to provide stability against multiple
pulsing and limits maximum switching frequency during
transient events.
Enable
The enable pin can be driven with an external logic
signal, connected to a resistive divider from PVIN/Vin to
ground to create an Under-Voltage Lockout (UVLO)
based on the PVIN/VIN supply, or connected to
PVIN/VIN through a single resistor to auto-enable while
operating within the EN pin internal clamp current sink
capability.
The EN pin can be directly driven by logic voltages of
5 V, 3.3 V, 2.5 V, etc. If the EN pin is driven by 5 V logic,
a small current flows into the pin when the EN pin
voltage exceeds the internal clamp voltage of 4.3 V. To
eliminate clamp current flowing into the EN pin use a
voltage divider to limit the EN pin voltage to < 4 V.
To implement the UVLO function based on PVIN/VIN
voltage level, select values for R7 and R8 in Figure 1
such that the tap point reaches 1.26 V when VIN reaches
the desired startup level using the following equation:
(1)
where VIN,on is the input voltage for startup and VEN,on
is the EN pin rising threshold of 1.26 V. With R8
selected as 10 kΩ, and VIN,on=9 V the value of R7 is
61.9 kΩ.
The EN pin can be pulled high with a single resistor
connected from VIN to the EN pin. With VIN > 5.5V a
series resistor is required to limit the current flow into
the EN pin clamp to less than 24 µA to keep the internal
clamp within normal operating range. The resistor value
can be calculated from the following equation:
(2)
Constant On-time Modulation
The FAN23SV06A uses a constant on-time modulation
technique, in which the HS MOSFET is turned on for a
fixed time, set by the modulator, in response to the input
voltage and the frequency-setting resistor. This on-time
is proportional to the desired output voltage, divided by
the input voltage. With this proportionality, the frequency
is essentially constant over the load range where
inductor current is continuous.
For buck converter in Continuous Conduction Mode
(CCM), the switching frequency fSW is expressed as:
(3)
The on-time generator sets the on-time (tON) for the
high-side MOSFET, which results in the switching
frequency of the regulator during steady-state operation.
To maintain a relatively constant switching frequency
over a wide range of input conditions, the input voltage
information is fed into the on-time generator.
tON is determined by:
(4)
where ItON is:
(5)
where RFREQ is the frequency-setting resistor
described in the Setting Switching Frequency section;
CtON is the internal 2.2 pF capacitor; and ItON is the VIN
feed-forward current that generates the on-time.
The FAN23SV06A implements open-circuit detection on
the FREQ pin to protect the output from an infinite on-
time. In the event the FREQ pin is left floating, switching
of the regulator is disabled. The FAN23SV06A is
designed for VIN input range of 7 V to 18 V and fSW from
200 kHz to 1.5 MHz, resulting in an ItON ratio of 1 to 16.
As the ratio of VOUT to VIN increases, tOFF,min introduces a
limit on the maximum switching frequency as calculated
in the following equation, where the factor 1.2 is
included in the denominator to provide some headroom
for transient operation:
(6)
Soft-Start (SS)
A conventional soft-start ramp is implemented to provide
a controlled startup sequence of the output voltage. A
current is generated on the SS pin to charge an external
capacitor. The lesser of the voltage on the SS pin and
the reference voltage is used for output regulation.
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 14
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
To reduce VOUT ripple and achieve a smoother ramp of
the output voltage, tON is modulated during soft-start. tON
starts at 50% of the steady-state on-time (PWM Mode)
and ramps up to 100% gradually.
During normal operation, the SS voltage is clamped to
400 mV above the FB voltage. The clamp voltage drops
to 40 mV during an overload condition to allow the
converter to recover using the soft-start ramp once the
overload condition is removed. On-time modulation
during SS is disabled when an overload condition exists.
To maintain a monotonic soft-start ramp, the regulator is
forced into PFM Mode during soft-start. The minimum
frequency clamp is disabled during soft-start.
The nominal startup time is programmable through an
internal current source charging the external soft-start
capacitor CSS:
(7)
where:
CSS
=
External soft-start programming capacitor;
ISS
=
Internal soft-start charging current source,
10 A;
tSS
=
Soft-start time; and
VREF
=
600 mV
For example; for 1 ms startup time, CSS=15 nF.
The soft-start option can be used for ratiometric tracking.
When EN is LOW, the soft-start capacitor is discharged.
Startup on Pre-Bias
FAN23SV06A allows the regulator to start on a pre-bias
output, VOUT, and ensures VOUT is not discharged during
the soft-start operation. To guarantee no glitches on
VOUT at the beginning of the soft-start ramp, LS is
disabled until the first positive-going edge of the PWM
signal. The regulator is forced into PFM Mode during
soft-start to ensure the inductor current remains
positive, reducing the possibility of discharging the
output voltage. FAN23SV06PA does not support startup
with prebias on output.
Internal Linear Regulator
The FAN23SV06A includes a linear regulator to
facilitate single-supply operation for self-biased
applications. PVCC is the linear regulator output and
supplies power to the internal gate drivers. The PVCC
pin should be bypassed with a 2.2 µF ceramic
capacitor. The device can operate from a 5 V rail if the
VIN, PVIN, and PVCC pins are connected together to
bypass the internal linear regulator.
VCC Bias Supply and UVLO
The VCC rail supplies power to the controller. It is
generally connected to the PVCC rail through a low-
pass filter of a 10 resistor and 0.1 µF capacitor to
minimize any noise sources from the driver supply.
An Under-Voltage Lockout (UVLO) circuit monitors the
VCC voltage to ensure proper operation. Once the VCC
voltage is above the UVLO threshold, the part begins
operation after an initialization routine of 50 µs. There is
no UVLO circuitry on either the PVCC or VIN rails.
Pulse Frequency Modulation (PFM)
One of the key benefits of using a constant on-time
modulation scheme is the seamless transitions in and
out of Pulse Frequency Modulation (PFM) Mode. The
PWM signal is not slave to a fixed oscillator and,
therefore, can operate at any frequency below the target
steady-state frequency. By reducing the frequency
during light-load conditions, efficiency can be
significantly improved. If the PFM operation with
associated frequency reduction is not desired, select the
FAN23SV06PA with Forced PWM Mode.
The FAN23SV06A provides a Zero-Crossing Detector
(ZCD) circuit to identify when the current in the inductor
reverses direction. To improve efficiency at light load,
the LS MOSFET is turned off around the zero crossing
to eliminate negative current in the inductor. For
predictable operation entering PFM mode the controller
waits for nine consecutive zero crossings before
allowing the LS MOSFET to turn off in the
FAN23SV06A.
In PFM Mode, fSW varies or modulates proportionally to
the load; as load decreases, fSW also decreases. The
switching frequency, while the regulator is operating in
PFM, can be expressed as:
(8)
where L is inductance and IOUT is output load current.
Minimum Frequency Clamp
To maintain a switching frequency above the audible
range, the FAN23SV06A clamps the switching
frequency to a minimum value of 18 kHz. The LS
MOSFET is turned on to discharge the output and
trigger a new PWM cycle. The minimum frequency
clamp is disabled during soft-start.
Protection Features
The converter output is monitored and protected against
over-current, over-voltage, under-voltage, and high-
temperature conditions.
Over-Current Protection (OCP)
The FAN23SV06A uses current information through the
LS to implement valley-current limiting. While an OC
event is detected, the HS is prevented from turning on
and the LS is kept on until the current falls below the
user-defined set point. Once the current is below the set
point, the HS is allowed to turn on.
During an OC event, the output voltage may droop if the
load current is greater than the current the converter is
providing. If the output voltage drops below the UV
threshold, an overload condition is triggered. During an
overload condition, the SS clamp voltage is reduced to
40 mV and the on-time is fixed at the steady-state
duration. By the nature of the control method; as VOUT
drops, the switching frequency is lower due to the
reduced rate of inductor current decay during the off-time.
The ILIM pin has an open-detection circuit to provide
protection against operation without a current limit.
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 15
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Under-Voltage Protection (UVP)
If VFB is below the under-voltage threshold of -11% VREF
(534 mV), the part enters UVP and PGOOD pulls LOW.
Over-Voltage Protection (OVP)
There are two levels of OV protection: +11% and +22%.
During an over-voltage event, PGOOD pulls LOW.
When VFB is > +11% of VREF (666 mV), both HS and LS
turn off. By turning off the LS during an OV event, VOUT
overshoot can be reduced when there is positive
inductor current by increasing the rate of discharge.
Once the VFB voltage falls below VREF, the latched OVP
signal is cleared and operation returns to normal.
A second over-voltage detection is implemented to
protect the load from more serious failure. When VFB
rises +22% above the VREF (732 mV), the HS latches off
until a power cycle on VCC and the LS is forced on until
530mV of VFB.
Over-Temperature Protection (OTP)
The FAN23SV06A incorporates an over-temperature
protection circuit that disables the converter when the
die temperature reaches 155°C. The IC restarts when
the die temperature falls below 140°C.
Power Good (PGOOD)
The PGOOD pin serves as an indication to the system
that the output voltage of the regulator is stable and
within regulation. Whenever VOUT is outside the
regulation window or the regulator is at over-
temperature (UV, OV, and OT), the PGOOD pin is
pulled LOW.
PGOOD is an open-drain output that asserts LOW when
VOUT is out of regulation or when OT is detected.
Application Information
Stability
Constant on-time stability consists of two parameters:
stability criterion and sufficient signal at VFB.
Stability criterion is given by:
(9)
Sufficient signal requirement is given by:
(10)
where IIND is the inductor current ripple and VFB is
the ripple voltage on VFB, which should be ≥12 mV.
In certain applications, especially designs utilizing only
ceramic output capacitors, there may not be sufficient
ripple magnitude available on the feedback pin for
stable operation. In this case, an external circuit
consisting of 2 resistors (R2 and R6) and 2 capacitors
(C4 and C5) can be added to inject ripple voltage into
the FB pin (See Figure 1).
There are some specific considerations when selecting
the RCC ripple injector circuit. For typical applications,
use 4.99 kΩ for R6, the value of C4 can be selected as
0.1 µF and approximate values for R2 and C5 can be
determined using the following equations.
R2 must be small enough to develop 12 mV of ripple:
(11)
R2 must be selected such that the R2C4 time constant
enables stable operation:
(12)
The minimum value of C5 can be selected to minimize
the capacitive component of ripple appearing on the
feedback pin:
(13)
Using the minimum value of C5 generally offers the best
transient response, and 100 pF is a good initial value in
many applications. Under some operating conditions,
excessive pulse jitter may be observed. To reduce jitter
and improve stability, the value of C5 can be increased:
(14)
5 V PVCC
The PVCC is the output of the internal regulator that
supplies power to the drivers and VCC. It is crucial to keep
this pin decoupled to PGND with a ≥1 µF X5R or X7R
ceramic capacitor. Because VCC powers internal analog
circuit, it is filtered from PVCC with a 10 Ω resistor and
0.1 µF X7R decoupling ceramic capacitor to AGND.
Setting the Output Voltage (VOUT)
The output voltage VOUT is regulated by initiating a high-
side MOSFET on-time interval when the valley of the
divided output voltage appearing at the FB pin reaches
VREF. Since this method regulates at the valley of the
output ripple voltage, the actual DC output voltage on
VOUT is offset from the programmed output voltage by the
average value of the output ripple voltage. The initial VOUT
setting of the regulator can be programmed from 0.6 V to
5.5 V by an external resistor divider (R3 and R4):
(15)
where VREF is 600 mV.
For example; for 1.2 V VOUT and 10 k R3, then R4 is
10 k. For 600 mV VOUT, R4 is left open. VFB is trimmed
to a value of 596 mV when VREF=600 mV, so the the
final output voltage, including the effect of the output
ripple voltage, can be approximated by the equation:
(16)
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN23SV06A • Rev. 1.0 16
FAN23SV06AMPX/ FAN23SV06PAMPX — 6 A Synchronous Buck Regulator
Setting the Switching Frequency (fSW)
fSW is programmed through external RFREQ as follows:
(17)
where CtON=2.2 pF internal capacitor that generates
tON. For example; for fSW=500 kHz and VOUT=1.2 V,
select a standard resistor value for RFREQ=54.9 k.
Inductor Selection
The inductor is typically selected based on the ripple
current (IL), which is usually selected as 25% to 45% of
the maximum DC load. The inductor current rating
should be selected such that the saturation and heating
current ratings exceed the intended currents
encountered in the application over the expected
temperature range of operation. Regulators that require
fast transient response use smaller inductance and
higher current ripple; while regulators that require higher
efficiency keep ripple current on the low side.
The inductor value is given by: