FAN6520A Single Synchronous Buck PWM Controller
October 2006
FAN6520A
Single Synchronous Buck PWM Controller
Features
■
Output Range: 0.8V to V
IN
Description
The FAN6520A simplifies implementing a complete con-
trol and protection scheme for a DC-DC stepdown con-
verter. Designed to drive N-channel MOSFETs in a
synchro-nous buck topology, the FAN6520A integrates
the control, output adjustment, monitoring, and protec-
tion functions into a single 8-lead package.
The FAN6520A employs a single feedback loop and volt-
age-mode control with fast transient response. The out-
put 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-frequency oscillator
reduces design complexity, while balancing typical appli-
cation cost. The error amplifier features a 15MHz gain-
bandwidth product and an 8V/µs slew rate, which
enables high converter bandwidth for fast transient per-
formance. The resulting PWM duty cycles range from
0% to 100%.
The IC monitors the drop across the upper MOSFET and
inhibits PWM operation appropriately to protect against
over-current conditions. This approach simplifies the
implementation and improves efficiency by eliminating
the need for a current sense resistor.
The FAN6520A is rated for operation from 0° to +70°C,
with the FAN6520AI 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
Lossless, Programmable, Over-Current Protection
– Uses Upper MOSFET’s R
DS(ON)
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
Ordering Information
Part Number
FAN6520AM
FAN6520AMX
FAN6520AIM
FAN6520AIMX
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
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
FAN6520A Single Synchronous Buck PWM Controller
Pin Configuration
BOOT
HDRV
GND
LDRV
1
2
3
4
FAN6520A
8
7
6
5
SW
COMP/OCSET/SD
FB
VCC
FAN6520AM 8-Pin SOIC Package
Pin Definitions
Pin #
1
2
Name
BOOT
HDRV
Description
Bootstrap Supply Input.
Provides a boosted voltage to the high-side MOSFET driver.
Connect to bootstrap capacitor, as shown in Figure 1.
High-Side Gate-Drive Output.
Connect to the gate of the high-side power MOSFET(s).
This pin is 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 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 ceramic
capacitor as close to this pin as possible.
Feedback.
This pin is the inverting input of the internal error amplifier. Use this pin, in com-
bination with the COMP/OCSET pin, to compensate the voltage-control feedback loop of
the converter.
Compensation / Over-Current Set Point / Shut Down.
This is a multiplexed pin. During
operation, the output of the error amplifier drives this pin. During a short period of time fol-
lowing power-on reset (POR), this pin is used to determine the over-current threshold of the
converter. Pulling COMP/OCSET 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 restart.
Switch Node Input.
The SW pin provides return for the high-side bootstrapped driver, is a
sense point for the adaptive shoot-through protection, and is used to monitor the drop
across the upper MOSFET’s R
DS(ON)
for current limit. Connect as shown in Figure 1.
3
GND
4
LDRV
5
6
VCC
FB
7
COMP/
OCSET/SD
8
SW
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
2
FAN6520A Single Synchronous Buck PWM Controller
Typical Application
+5V
D
BOOT
1
VCC
C
VCC
BOOT
C
BOOT
C
BULK
Q1
2
HDRV
SW
Q2
LDRV
GND
FB
R
S
R
OFFSET
L
OUT
+V
OUT
C
OUT
C
HF
5
R
OCSET
FAN6520A
8
4
3
COMP/OCSET
7
6
R
F
C
F
C
I
Figure 1. Typical Application
VCC
POR / SOFT-START
INHIBIT
BOOT
HDRV
SW
SAMPLE
& HOLD
OC
COMP/OCSET
FB
20A
ERROR
AMP
0.8V
PWM
PWM
GATE
CONTROL
LOGIC
V
CC
LDRV
GND
OSC
Figure 2. Functional Block Diagram
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
3
FAN6520A Single Synchronous Buck PWM Controller
Absolute Maximum Ratings
The “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. The
device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables
are not guaranteed at the absolute maximum ratings. The “Recommended Operating Conditions” table defines the
conditions for actual device operation.
Parameter
VCC to GND
VBOOT to GND
HDRV (V
BOOT
– V
SW
)
LDRV
SW to PGND
All other pins
Continuous
Transient ( t < 50ns, F < 500kHz)
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
Symbol
T
STG
T
L
Parameter
Storage Temperature
Lead Soldering Temperature, 10 seconds
Vapor Phase, 60 seconds
Infrared, 15 seconds
Min.
–65
Typ.
Max.
150
300
215
220
715
Units
°C
°C
°C
°C
mW
°C/W
°C/W
P
D
Θ
JC
Θ
JA
Power Dissipation, T
A
= 25°C
Thermal Resistance, Junction-to-Case
Thermal Resistance, Junction-to-Ambient
40
140
Recommended Operating Conditions
Symbol
V
CC
T
A
T
J
Parameter
Supply Voltage
Ambient Temperature
Junction Temperature
Conditions
VCC to PGND
FAN6520A
FAN6520AI
Min.
4.5
0
–40
–40
Typ.
5
Max.
5.5
70
85
125
Units
V
°C
°C
°C
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
4
FAN6520A Single Synchronous Buck PWM Controller
Electrical Specifications
V
CC
= 5V and T
A
= 25°C, using the circuit shown in Figure 1 unless otherwise noted. The • denotes specifications that
apply over the full operating temperature range.
Symbol Parameter
Supply Current
I
VCC
POR
Oscillator
F
OSC
ΔV
OSC
Reference
V
REF
Reference Voltage
Frequency
Ramp Amplitude
V
CC
Current
Rising VCC POR Threshold
VCC POR Threshold Hysteresis
Conditions
HDRV, LDRV open
•
•
Min.
1.5
4.00
Typ.
2.4
4.22
170
Max.
3.8
4.45
Units
mA
V
mV
Power-On Reset
FAN6520A
FAN6520AI
•
•
•
250
230
300
300
1.5
340
340
kHz
kHz
Vp-p
T
A
= 0 to 70°C
FAN6520AI
•
•
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
Error Amplifier
DC Gain
GBWP
S/R
R
HUP
R
HDN
R
LUP
R
LDN
I
OCSET
Gain – Bandwidth Product
Slew Rate
HDRV Pulll-Up Resistance
HDRV Pull-Down Resistance
LDRV Pull-Up Resistance
LDRV Pull-Down Resistance
OCSET Current Source
FAN6520A
FAN6520AI
V
DISABLE
Disable Threshold
•
•
17
14
Gate Drivers
Protection/Disable
20
20
800
22
24
μA
μA
mV
Notes:
1. All limits at operating temperature extremes are guaranteed by design, characterization, and statistical quality
control.
2. AC specifications guaranteed by design/characterization (not production tested).
© 2005 Fairchild Semiconductor Corporation
FAN6520A Rev. 1.0.5
www.fairchildsemi.com
5
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