www.fairchildsemi.com
FAN5037
Adjustable Switching Regulator Controller
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
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.
Applications
•
•
•
•
I/O and AGP power for desktop computers
High efficiency power for ASICs
High efficiency power for DSPs
Adjustable step-down power supplies
Block Diagram
5V
VCCA 2
IFBL 4
+12V
+5V
FAN5037
Feedback Control
IFBH 3
VCCP 8
CEXT
1
Oscillator
Digital Logic
7
DRV
Vout
1.20V
Reference
VFB 5
GNDP 6
REV. 1.0.3 9/26/01
FAN5037
PRODUCT SPECIFICATION
Pin Assignments
CEXT
VCCA
IFBH
IFBL
1
2
3
4
8
7
6
5
VCCP
DRV
GNDP
VFB
FAN5037
Pin Descriptions
Pin
Name
CEXT
Pin
Number
1
Pin Function Description
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.
Analog V
cc
.
Power supply for regulator control circuitry and voltage reference. Connect to
system 5V supply and decouple to ground with 0.1µF ceramic capacitor.
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.
Low side current feedback.
See Applications Information for details.
Voltage feedback.
Using two external resistors, this pin sets the output voltage level for the
switching regulator.
Power Ground.
Connect to a low impedance ground. See Application Information for
details.
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.
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.
VCCA
IFBH
2
3
IFBL
VFB
GNDP
DRV
4
5
6
7
VCCP
8
Absolute Maximum Ratings
Supply Voltages, VCCA
Supply Voltages, VCCP
Junction Temperature, T
J
Storage Temperature, T
S
Lead Soldering Temperature, 10 seconds
Thermal Resistance Junction-to-Ambient,
Θ
JA
7V
13V
+150°C
-65 to +150°C
300°C
163°C/W
Note:
1. Functional operation under any of these conditions is not implied. Performance is guaranteed only if Operating Conditions
are not exceeded.
Operating Conditions
Parameter
Switching Regulator Supply, VCCA
Ambient Operating Temperature, T
A
Gate Drive Supply, VCCP
Conditions
Min.
4.75
0
9.5
12
Typ.
5
Max.
5.25
70
12.6
Units
V
°C
V
2
REV. 1.0.3 9/26/01
PRODUCT SPECIFICATION
FAN5037
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.
Parameter
Output Voltage
Output Temperature Drift
Line Regulation
Load Regulation
V
OUT
PSRR
Output Ripple, peak-peak
Total DC Accuracy
1
Efficiency
Output Driver Current
Short Circuit Threshold Voltage
Undervoltage Lockout
On Time Pulse Width
2
VCCA Supply Current
VCCP Supply Current
C
EXT
= 180pF
Independent of load
I
LOAD
= 13A
•
•
I
LOAD
= 5A
Open Loop
•
•
•
T
A
= 0˚C–70˚C
VCCA = 4.75 to 5.25V, I
LOAD
= 13A
I
LOAD
= 0 to 5A or 5A to 13A
VCCA = 4.75 to 5.25V
20MHz BW, I
LOAD
= 13A
•
80
0.5
70
3.5
90
4.0
3.5
5
20
15
25
100
4.5
60
15
±55
85
±100
Conditions
Min.
1.2
40
3
30
5
43
Typ.
Max.
3.6
Units
V
ppm/˚C
mV
mV
dB
mV
mV
%
A
mV
V
µs
mA
mA
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
.
REV. 1.0.3 9/26/01
3
FAN5037
PRODUCT SPECIFICATION
Typical Operating Characteristics
(VCCA = 5V, and T
A
= +25
°
C using circuit in Figure 1, unless otherwise noted)
Efficiency vs. Output Current
95
94
93
92
91
90
89
88
87
86
85
1
2
3
4
5
6
7
8
9
10
Output Current
+1.5
+1.0
V
OUT
(%)
+0.5
Nom
-0.5
-1.0
-1.5
0
2
4
6
8
10
Output Current (A)
Output Voltage vs. Load
Efficiency (%)
Output Voltage vs. Temperature, I
OUT
= 10A
+0.50
Output Voltage (%)
+0.25
Nom.
-0.25
-0.50
0
25
50
75
100
125
Transient Response, 0.5 to 5.5A
I
SW
(2A/div) VOUT (50mV/div)
Output Ripple, I
OUT
= 10A)
Time (100µs/division)
V
OUT
(10mV/division)
Time (2µs/division)
4
REV. 1.0.3 9/26/01
PRODUCT SPECIFICATION
FAN5037
Typical Operating Characteristics
(continued)
Output Startup, System Power-Up
Pin 7 (DRV), 10A Load
Time (5ms/division)
Time (1µs/division)
Pin 7 (DRV), 0.1A Load
Time (1µs/division)
Application Circuit
Optional
L1
+5V
2.5µH
+C2
+C4
+ C3
1200µF 1200µF 1200µF
C8
0.1µF
+12V
C1
0.1µF
R1
47Ω C5
D2
MMBD4148
D3
1N4735A
1µF
FDB6030L
Q1
R2 4.7Ω
D1
L2
4.7µH
R3
5.2mΩ
R4
3.48KΩ
+
V
CORE
C7
0.1uF
C6
180pF
8
1
7
2
U1
3 FAN5037 6
5
4
...
MBRB1545CT
+ C14
1500µF
R5
2KΩ
Figure 1. 13A at 3.3V Application Schematic
REV. 1.0.3 9/26/01
5
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