2006 Fairchild Semiconductor Corporation
1
www.fairchildsemi.com
February 2006
FAN6520B Rev. 1.0.3
F
AN6520B Single Sync
hr
onous Buc
k PWM Contr
oller
FAN6520B
Single Synchronous Buck PWM Controller
Features
Accepts 1.5V to 5V for V
IN
Output Range 0.8V to V
IN
0.8V Internal Reference
1.5% Over Line Voltage and Temperature
Drives N-Channel MOSFETs
Simple Single-Loop Control Design
Voltage-Mode PWM Control
Fast Transient Response
High-Bandwidth Error Amplifier
Full 0% to 100% Duty Cycle
Small Converter Size
300kHz Fixed Frequency Oscillator
Internal Soft-Start
8-Lead SOIC
Applications
Power Supplies for PC Subsystems and Peripherals
MCH, GTL, and AGP Supplies
Cable Modems, Set Top Boxes, and DSL Modems
DSP, Memory
Low-Voltage Distributed Power Supplies
ACPI Power Control
5V Input DC-DC Regulator
Description
The FAN6520B makes simple work out of implementing
a complete control and protection scheme for a DC-DC
stepdown converter.
Designed to drive N-channel MOSFETs in a synchro-
nous buck topology, the FAN6520B integrates the con-
trol, output adjustment, and monitoring functions into a
single 8-lead package.
The FAN6520B is easy to use, employs a single feed-
back loop, and voltage-mode control with fast transient
response. The output voltage can be precisely regulated
to as low as 0.8V, with a maximum tolerance of 1.5%
over temperature and line voltage variations. A fixed fre-
quency oscillator reduces design complexity, while bal-
ancing typical application cost. The error amplifier
features a 15MHz gain-bandwidth product and an 8V/s
slew rate which enables high converter bandwidth for
fast transient performance. The resulting PWM duty
cycles range from 0% to 100%.
The FAN6520B is rated for operation from 0 to +70C
with the FAN6520BI rated from 40 to +85C.
Ordering Information
Part Number
Temperature Range
Package
Packing
FAN6520BM
0C to 70C
SOIC-8
Rails
FAN6520BMX
0C to 70C
SOIC-8
Tape and Reel
FAN6520BIM
40C to 85C
SOIC-8
Rails
FAN6520BIMX
40C to 85C
SOIC-8
Tape and Reel
2
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FAN6520B Rev. 1.0.3
F
AN6520B Single Sync
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Pin Configuration
FAN6520BM 8-pin SOIC Package
Pin Definitions
Pin #
Pin Name
Pin Function Description
1
BOOT
Bootstrap Supply Input.
Provides a boosted voltage to the high-side MOSFET driver.
Connect to bootstrap capacitor and diode as shown in Figure 1.
2
HDRV
High Side Gate Drive Output.
Connect to the gate of the high-side power MOSFET(s).
This pin is also monitored by the adaptive shoot-through protection circuitry to determine
when the upper MOSFET has turned off.
3
GND
Ground.
The signal and power ground for the IC. Tie this pin to the ground island/plane
through the lowest impedance connection available. Connect directly to source of low-side
MOSFET(s).
4
LDRV
Low Side Gate Drive Output.
Connect to the gate of the low-side power MOSFET(s).
This pin is also monitored by the adaptive shoot-through protection circuitry to determine
when the lower MOSFET has turned off.
5
VCC
VCC.
Provides bias power to the IC and the drive voltage for LDRV. Bypass with a good
quality ceramic capacitor (X7R or X5R) as close to this pin as possible.
6
FB
Feedback.
This pin is the inverting input of the internal error amplifier. Use this pin, in
combination with the COMP pin, to compensate the voltage-control feedback loop of the
converter.
7
COMP/SD
COMP/SD.
This is a multiplexed pin. During operation, the output of the error amplifier
drives this pin. Pulling COMP to a level below 0.8V disables the controller. Disabling the
controller causes the oscillator to stop, the HDRV and LDRV outputs to be held low, and the
soft-start circuitry to re-arm. Connect a 75k
resistor between VCC and COMP/SD pin to
pull up.
8
SW
Switch Node Input.
Connect as shown in Figure 1. The SW pin provides return for the
high-side bootstrapped driver, is a sense point for the adaptive shoot-thru protection.
FAN6520B
1
2
3
4
8
7
6
5
SW
COMP/SD
FB
VCC
BOOT
HDRV
GND
LDRV
3
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FAN6520B Rev. 1.0.3
F
AN6520B Single Sync
hr
onous Buc
k PWM Contr
oller
Typical Application
Figure 1. Typical Application
Figure 2. Functional Block Diagram
FAN6520B
FB
VCC
+V
OUT
Q2
COMP/SD
R
S
GND
LDRV
SW
HDRV
BOOT
5
3
4
8
2
1
6
7
Q1
R
OFFSET
R
PULLUP
C
F
R
F
C
I
C
BOOT
D
BOOT
C
VCC
+5V
L
OUT
C
OUT
C
HF
C
BULK
Vin = 1.5V to 5V
INHIBIT
PWM
0.8V
ERROR
AMP
VCC
OSC
GATE
CONTROL
LOGIC
FB
PWM
POR / SOFT START
VCC
COMP/SD
GND
LDRV
SW
HDRV
BOOT
4
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FAN6520B Rev. 1.0.3
F
AN6520B Single Sync
hr
onous Buc
k PWM Contr
oller
Absolute Maximum Ratings
Absolute maximum ratings are the values beyond which the device may be damaged or have its useful life impaired.
Functional operation under these conditions is not implied.
Thermal Information
Recommended Operating Conditions
Parameter
Min.
Max.
Units
VCC to GND
6
V
VBOOT to GND
15
V
HDRV (V
BOOT
V
SW
)
6
V
LDRV
0.5
6
V
SW to PGND
Continuous
0.5
6
V
Transient ( t < 50nsec)
3
7
V
All other pins
5.5
V
Parameter
Min.
Typ.
Max.
Units
Storage Temperature
65
150
C
Lead Soldering Temperature, 10 seconds
300
C
Vapor Phase, 60 seconds
215
C
Infrared, 15 seconds
220
C
Power Dissipation (P
D
), T
A
= 25C
715
mW
Thermal Resistance Junction to Case
JC
40
C/W
Thermal Resistance Junction to Ambient
JA
140
C/W
Parameter
Conditions
Min.
Typ.
Max.
Units
Supply Voltage VCC
VCC to PGND
4.5
5
5.5
V
Ambient Temperature (T
A
)
FAN6520B
0
70
C
FAN6520BI
40
85
C
Junction Temperature (T
J
)
40
125
C
5
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FAN6520B Rev. 1.0.3
F
AN6520B Single Sync
hr
onous Buc
k PWM Contr
oller
Electrical Specifications
VCC = 5V, and TA = 25C using circuit in Figure 1 unless otherwise noted. The denotes specifications which apply
over the full operating temperature range.
Notes:
1. All limits at operating temperature extremes are guaranteed by design, characterization and statistical quality
control.
2. Specifications guaranteed by design/characterization (not production tested).
3. To ensure shutdown, COMP/SD pin should be held below 400mV while sinking 6mA of current.
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Units
Supply Current
VCC Current
I
VCC
HDRV, LDRV open
1.5
2.4
3.8
mA
Power-On Reset
Rising VCC POR Threshold
POR
4.00
4.22
4.45
V
VCC POR Threshold Hysteresis
170
mV
Oscillator
Frequency
F
OSC
FAN6520B
250
300
340
kHz
FAN6520BI
230
300
340
kHz
Ramp Amplitude
V
OSC
1.5
Vp-p
Reference
Reference Voltage
V
REF
T
A
= 0 to 70C
788
800
812
mV
FAN6520BI
780
800
820
mV
Error Amplifier
DC Gain
Note 2
88
dB
Gain Bandwidth Product
GBW
Note 2
15
MHz
Slew Rate
S/R
Note 2
8
V/s
Gate Drivers
HDRV pull-up resistance
R
HUP
2.5
HDRV pull-down resistance
R
HDN
2.0
LDRV pull-up resistance
R
LUP
2.5
LDRV pull-down resistance
R
LDN
1.0
Disable
Disable Threshold
V
DISABLE
Note 3
400
800
mV
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