www.fairchildsemi.com
REV. 1.0.3 9/26/01
Features
High power switch-mode DC-DC controller can provide
in excess of 13A
Output voltage adjustable from 1.2V to 3.6V
85% efficiency
Cumulative accuracy < 3% over line, load, and
temperature variations
Overvoltage and short circuit protection
Built-in soft start
No overshoot at turn-on
Applications
I/O and AGP power for desktop computers
High efficiency power for ASICs
High efficiency power for DSPs
Adjustable step-down power supplies
Description
The FAN5037 is a high power, switch-mode DC-DC control-
ler that provides efficient power for all low-voltage applica-
tions. This controller has a built-in Soft Start feature which
offers system protection during power-up by reducing both
inrush current and output overshoot. When combined with
the appropriate external circuitry, the FAN5037 can deliver
load currents as high as 13A at efficiencies as high as 88%.
The FAN5037 can generate output voltages from 1.2V up to
3.6V using external resistors.
The FAN5037 is designed to operate in a constant on-time
control mode under all load conditions. Its accurate low TC
reference eliminates the need for precision external compo-
nents in order to achieve the tight tolerance voltage regula-
tion required by many applications. Short circuit current
protection is provided through the use of a current sense
resistor, while overvoltage protection is provided internally.
Block Diagram
Feedback Control
Oscillator
Digital Logic
FAN5037
1.20V
Reference
Vout
+12V
5V
+5V
1
CEXT
VCCA 2
IFBL 4
IFBH 3
VCCP 8
7
DRV
GNDP 6
VFB 5
FAN5037
Adjustable Switching Regulator Controller
FAN5037
PRODUCT SPECIFICATION
2
REV. 1.0.3 9/26/01
Pin Assignments
Absolute Maximum Ratings
Note:
1. Functional operation under any of these conditions is not implied. Performance is guaranteed only if Operating Conditions
are not exceeded.
Operating Conditions
Pin Descriptions
Pin
Name
Pin
Number
Pin Function Description
CEXT
1
External capacitor.
A 180pF capacitor is connected to this pin as part of the constant
on-time pulse width circuit. Careful layout of this pin is critical to system performance.
See Applications Information for details.
VCCA
2
Analog V
cc
.
Power supply for regulator control circuitry and voltage reference. Connect to
system 5V supply and decouple to ground with 0.1F ceramic capacitor.
IFBH
3
High side current feedback.
Pins 3 and 4 are used as the inputs for the current feedback
control loop and as the short circuit current sense points. Careful layout of the traces from
these pins to the current sense resistor is critical for optimal performance of the short circuit
protection scheme. See Applications Information for details.
IFBL
4
Low side current feedback.
See Applications Information for details.
VFB
5
Voltage feedback.
Using two external resistors, this pin sets the output voltage level for the
switching regulator.
GNDP
6
Power Ground.
Connect to a low impedance ground. See Application Information for
details.
DRV
7
MOSFET driver output.
Connect this pin to the gate of the N-channel MOSFET Q1 as
shown in Figure 12. The trace from this pin to the MOSFET gate should be kept as short as
possible (less than 0.5"). See Applications Information for details.
VCCP
8
Power V
cc
.
Power supply for DRV output driver. Connect to system 12V supply with R-C
filter shown in Figure 12. See Applications Information for details.
Supply Voltages, VCCA
7V
Supply Voltages, VCCP
13V
Junction Temperature, T
J
+150C
Storage Temperature, T
S
-65 to +150C
Lead Soldering Temperature, 10 seconds
300C
Thermal Resistance Junction-to-Ambient,
JA
163C/W
Parameter
Conditions
Min.
Typ.
Max.
Units
Switching Regulator Supply, VCCA
4.75
5
5.25
V
Ambient Operating Temperature, T
A
0
70
C
Gate Drive Supply, VCCP
9.5
12
12.6
V
CEXT
VCCA
IFBH
VCCP
DRV
GNDP
1
2
3
8
7
6
IFBL
VFB
FAN5037
4
5
PRODUCT SPECIFICATION
FAN5037
REV. 1.0.3 9/26/01
3
Electrical Characteristics
(VCCA = 5V, VCCP = 12V, T
A
= 25
C using circuit of Figure 1, unless otherwise noted)
The
denotes specifications which apply over the full ambient operating temperature range.
Notes:
1. Total DC accuracy includes setpoint accuracy, temperature drift, line and load regulation.
2. The on-time pulse width of the oscillator is set via external capacitor C
EXT
.
Parameter
Conditions
Min.
Typ.
Max.
Units
Output Voltage
1.2
3.6
V
Output Temperature Drift
T
A
= 0C70C
40
ppm/C
Line Regulation
VCCA = 4.75 to 5.25V, I
LOAD
= 13A
3
5
mV
Load Regulation
I
LOAD
= 0 to 5A or 5A to 13A
30
43
mV
V
OUT
PSRR
VCCA = 4.75 to 5.25V
60
dB
Output Ripple, peak-peak
20MHz BW, I
LOAD
= 13A
15
mV
Total DC Accuracy
1
55
100
mV
Efficiency
I
LOAD
= 5A
80
85
%
Output Driver Current
Open Loop
0.5
A
Short Circuit Threshold Voltage
70
90
100
mV
Undervoltage Lockout
3.5
4.0
4.5
V
On Time Pulse Width
2
C
EXT
= 180pF
3.5
s
VCCA Supply Current
Independent of load
5
15
mA
VCCP Supply Current
I
LOAD
= 13A
20
25
mA
FAN5037
PRODUCT SPECIFICATION
4
REV. 1.0.3 9/26/01
Typical Operating Characteristics
(VCCA = 5V, and T
A
= +25
C using circuit in Figure 1, unless otherwise noted)
Output Current (A)
Output Voltage vs. Load
V
OUT
(%)
0
2
4
6
8
Output Voltage vs. Temperature, I
OUT
= 10A
Nom.
+0.25
+0.50
-0.25
-0.50
0
25
50
75
Output Voltage (%)
10
+1.0
+0.5
Nom
-0.5
-1.0
-1.5
+1.5
100
125
Transient Response, 0.5 to 5.5A
I
SW
(2A/div)
V
OUT
(50mV/div)
Time (100
s/division)
Output Ripple, I
OUT
= 10A)
V
OUT
(10mV/division)
Time (2
s/division)
Efficiency vs. Output Current
95
94
93
92
91
90
89
88
87
86
85
Efficiency (%)
1
2
3
4
5
Output Current
6
7
8
9
10
PRODUCT SPECIFICATION
FAN5037
REV. 1.0.3 9/26/01
5
Typical Operating Characteristics
(continued)
Application Circuit
Figure 1. 13A at 3.3V Application Schematic
Pin 7 (DRV), 10A Load
Pin 7 (DRV), 0.1A Load
Time (1s/division)
Time (1s/division)
Output Startup, System Power-Up
Time (5ms/division)
+12V
C6
180pF
Q1
FDB6030L
+
D1
MBRB1545CT
L2
2.5
H
L1
4.7
H
R3
5.2m
R1
R2
47
4.7
C1
0.1
F
U1
FAN5037
2
3
4
1
7
6
5
8
C3
1200
F
D2
MMBD4148
D3
1N4735A
+5V
1
F
C5
0.1uF
C7
0.1
F
C8
+C4
1200
F
+C2
1200
F
V
CORE
+
+
1500
F
C14
...
R5
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