FAN6520B Single Synchronous Buck PWM Controller
February 2006
FAN6520B
Single Synchronous Buck PWM Controller
Features
■
Accepts 1.5V to 5V for V
IN
■
Output Range 0.8V to V
IN
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/µs
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 +70°C
with the FAN6520BI rated from –40° to +85°C.
■
■
■
■
– 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
Ordering Information
Part Number
FAN6520BM
FAN6520BMX
FAN6520BIM
FAN6520BIMX
Temperature Range
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
Package
SOIC-8
SOIC-8
SOIC-8
SOIC-8
Packing
Rails
Tape and Reel
Rails
Tape and Reel
©2006 Fairchild Semiconductor Corporation
1
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FAN6520B Rev. 1.0.3
FAN6520B Single Synchronous Buck PWM Controller
Pin Configuration
BOOT
HDRV
GND
LDRV
1
2
3
4
FAN6520B
8
7
6
5
SW
COMP/SD
FB
VCC
FAN6520BM 8-pin SOIC Package
Pin Definitions
Pin #
1
2
Pin Name
BOOT
HDRV
Pin Function Description
Bootstrap Supply Input.
Provides a boosted voltage to the high-side MOSFET driver.
Connect to bootstrap capacitor and diode as shown in Figure 1.
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.
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).
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.
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.
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.
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
Ω
resistor between VCC and COMP/SD pin to
pull up.
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.
3
GND
4
LDRV
5
6
VCC
FB
7
COMP/SD
8
SW
2
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FAN6520B Rev. 1.0.3
FAN6520B Single Synchronous Buck PWM Controller
Typical Application
+5V
BOOT
D
BOOT
C
BOOT
Vin = 1.5V to 5V
1
VCC
C
VCC
5
2
HDRV
SW
Q1
C
HF
C
BULK
L
OUT
Q2
R
PULLUP
FAN6520B
8
+V
OUT
C
OUT
4
3
COMP/SD
7
6
R
F
LDRV
GND
FB
R
S
R
OFFSET
C
F
C
I
Figure 1. Typical Application
VCC
POR / SOFT START
INHIBIT
BOOT
HDRV
SW
COMP/SD
FB
ERROR
AMP
PWM
PWM
GATE
CONTROL
LOGIC
0.8V
VCC
LDRV
OSC
GND
Figure 2. Functional Block Diagram
3
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FAN6520B Rev. 1.0.3
FAN6520B Single Synchronous Buck PWM Controller
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.
Parameter
VCC to GND
VBOOT to GND
HDRV (V
BOOT
– V
SW
)
LDRV
SW to PGND
All other pins
Continuous
Transient ( t < 50nsec)
Min.
Max.
6
15
6
Units
V
V
V
V
V
V
V
–
0.5
–
0.5
–
3
6
6
7
5.5
Thermal Information
Parameter
Storage Temperature
Lead Soldering Temperature, 10 seconds
Vapor Phase, 60 seconds
Infrared, 15 seconds
Power Dissipation (P
D
), T
A
= 25°C
Thermal Resistance – Junction to Case
θ
JC
Thermal Resistance – Junction to Ambient
θ
JA
40
140
Min.
–65
Typ.
Max.
150
300
215
220
715
Units
°C
°C
°C
°C
mW
°C/W
°C/W
Recommended Operating Conditions
Parameter
Supply Voltage VCC
Ambient Temperature (T
A
)
Junction Temperature (T
J
)
Conditions
VCC to PGND
FAN6520B
FAN6520BI
Min.
4.5
0
–
40
–
40
Typ.
5
Max.
5.5
70
85
125
Units
V
°C
°C
°C
4
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FAN6520B Rev. 1.0.3
FAN6520B Single Synchronous Buck PWM Controller
Electrical Specifications
VCC = 5V, and TA = 25°C using circuit in Figure 1 unless otherwise noted. The • denotes specifications which apply
over the full operating temperature range.
Parameter
Supply Current
VCC Current
Power-On Reset
Rising VCC POR Threshold
VCC POR Threshold Hysteresis
Oscillator
Frequency
Ramp Amplitude
Reference
Reference Voltage
Error Amplifier
DC Gain
Gain – Bandwidth Product
Slew Rate
Gate Drivers
HDRV pull-up resistance
HDRV pull-down resistance
LDRV pull-up resistance
LDRV pull-down resistance
Disable
Disable Threshold
Symbol
I
VCC
POR
Conditions
HDRV, LDRV open
•
•
Min.
1.5
4.00
Typ.
2.4
4.22
170
Max.
3.8
4.45
Units
mA
V
mV
F
OSC
∆
V
OSC
V
REF
FAN6520B
FAN6520BI
•
•
•
250
230
300
300
1.5
340
340
kHz
kHz
Vp-p
T
A
= 0 to 70°C
FAN6520BI
Note 2
•
•
788
780
800
800
88
15
8
2.5
2.0
2.5
1.0
812
820
mV
mV
dB
MHz
V/µs
Ω
Ω
Ω
Ω
mV
GBW
S/R
R
HUP
R
HDN
R
LUP
R
LDN
V
DISABLE
Note 2
Note 2
Note 3
400
800
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.
5
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FAN6520B Rev. 1.0.3
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