www.fairchildsemi.com
REV. 1.0.2 7/6/00
Features
Provides complete, low-cost core and I/O power in single
chip
I/O power sequencing
Core voltage adjustable from 1.5V to 3.6V
Independent adjustable current limits
Core up to 13A, I/O up to 5A
Precision trimmed low TC voltage reference
Constant On-Time oscillator
Small footprint 16 lead SOIC package
Applications
High efficiency low-cost power for DSPs
Power for ASICs and FPGAs
Programmable dual power supply for high current loads
Description
The FAN5038 provides a complete low-cost power system
for DSPs and other loads requiring high-performance. The
FAN5038 combines an adjustable switch-mode DC-DC
converter for core power with a low-dropout linear regulator
for I/O power in a space-saving SO-16 package. Simple
external circuitry provides power sequencing and indepen-
dent current limits. An internal precision voltage reference
allows the switcher to be adjusted from 1.5V to 3.6V. With
the appropriate external components, the FAN5038 can
deliver core power up to 13A, and I/O power up to 5A,
allowing multiple DSPs to be powered with a single device.
Block Diagram
FAN5038
+
Linear
Enable
Switcher
Select
Feedback
Control
Oscillator
Digital
Logic
Switching
Regulator
Linear Regulator
Core
I/O
1.5V
Reference
+12V
+5V
FAN5038
Dual Voltage Controller for DSP Power
FAN5038
PRODUCT SPECIFICATION
2
REV. 1.0.2 7/6/00
Pin Assignments
Pin Descriptions
Pin
Name
Pin
Number
Pin Function Description
LIN_EN
1
Linear regulator enable input.
Accepts TTL/open collector input levels. A logic level HIGH
on this pin disables the output of the linear regulator.
VREF
2
Voltage reference test point.
This pin provides access to the internal precision 1.5V
bandgap reference and should be decoupled to ground using a 0.1F ceramic capacitor.
No load should be connected to this pin.
IFBH
3
High side current feedback for switching regulator.
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 Discussion for details.
IFBL
4
Low side current feedback for switching regulator.
See Applications Discussion for
details.
FBSW
5
Voltage feedback for switching regulator.
This input is active when a logic level LOW is
input on pin 16 (SWCTRL). Using two external resistors, it sets the output voltage level for
the switching regulator. See Applications Discussion for details.
VCCA
6
Switching Regulator V
cc
.
Power supply for switching regulator control circuitry and
voltage reference. Connect to system 5V supply and decouple to ground with 0.1F
ceramic capacitor.
VFBL
7
Voltage feedback for linear regulator.
Using two external resistors, this pin sets the
output voltage level for the linear regulator. See Applications Discussion for details.
GNDP
8
Power Ground.
Return pin for high currents flowing in pins 9, 10 and 12 (SDRV, VCCP and
LDRV). Connect to a low impedance ground. See Applications Discussion for details.
SDRV
9
FET driver output for switching regulator.
Connect this pin to the gate of the N-channel
MOSFET Q1 as shown in Figure 1. The trace from this pin to the MOSFET gate should be
kept as short as possible (less than 0.5"). See Applications Discussion for details.
VCCP
10
Switching regulator gate drive V
cc
.
Power supply for SDRV output driver. Connect to
system 12V supply with R-C filter shown in Figure 1. See Applications Discussion for
details.
VCCL
11
Linear Regulator Vcc.
Power supply for LDRV output op-amp. Connect to system 12V
supply and decouple to ground with 0.1F ceramic capacitor.
LDRV
12
Output driver for linear regulator.
Connect this pin to the base of an NPN transistor.
When pin 1 (LIN_EN) is pulled HIGH, the linear regulator is disabled and pin 12 will be
pulled low internally.
VSCL
13
Low side current sense for linear regulator.
Connect this pin between the sense resistor
and the collector of the power transistor. The high side current sense is internally connected
to pin 6 (VCCA). Layout is critical to optimal performance of the linear regulator short circuit
protection scheme. See Applications Discussion for details.
LIN_EN
VREF
IFBH
IFBL
FBSW
VCCA
VFBL
SWCTRL
CEXT
GNDA
VSCL
LDRV
VCCL
VCCP
1
2
3
4
5
6
7
16
15
14
13
12
11
10
GNDP
SDRV
8
9
FAN5038
PRODUCT SPECIFICATION
3
REV. 1.0.2 7/6/00
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
GNDA
14
Analog ground.
All low power internal circuitry returns to this pin. This pin should be
connected to system ground so that ground loops are avoided. See Applications Discussion
for details.
CEXT
15
External capacitor.
A 100pF 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 Discussion for details.
SWCTRL
16
Switching regulator control input.
Accepts TTL/open collector input levels. A logic level
HIGH on this pin presets the switching regulator output voltage at 3.5V using internal
resistors. A logic level LOW on this pin will select the output voltage set by two external
resistors and the voltage feedback control pin 5 (VFBSW). See Applications Discussion for
details.
Supply Voltages, VCCA, VCCL, 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
112C/W
Parameter
Conditions
Min.
Typ.
Max.
Units
Switching Regulator V
CC
, VCCA
4.75
5
5.25
V
Linear Regulator V
CC
, VCCL
11.4
12
12.6
V
Logic Inputs, SWCTRL, LIN_EN
Logic HIGH
Logic LOW
2.4
0.8
V
V
Ambient Operating Temperature, T
A
0
70
C
Drive Gate Supply, V
CCP
9.5
12
12.6
V
Pin Descriptions
(continued)
Pin
Name
Pin
Number
Pin Function Description
PRODUCT SPECIFICATION
FAN5038
REV. 1.0.2 7/6/00
4
Electrical Characteristics--Switch-Mode Regulator
(VCCA = 5V, VCCL = 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. When the SWCTRL pin is HIGH or left open, the switch-mode regulator output will be preset at 3.5V using internal precision
resistors. When the SWCTRL pin is LOW, the output voltage may be programmed with external resistors. Please refer to
the Applications Section for output voltage selection information.
2. Setpoint accuracy is the initial output voltage variability under the specified conditions. When SWCTRL is LOW, the matching
of the external resistors will have a major influence on this parameter.
3. Cumulative DC accuracy includes setpoint accuracy, temperature drift, line and load regulation, and output ripple.
4. The on-time pulse width of the oscillator is preset using external capacitor C
EXT
. See Typical Operating Characteristics
curves.
Parameter
Conditions
Min.
Typ.
Max.
Units
Output Voltage, VOSW
1
SWCTRL = HIGH
Set by internal resistors
3.5
V
Output Voltage, VOSW
1
SWCTRL = LOW
Set by external resistors
1.5
3.6
V
Setpoint Accuracy
2
I
SW
= 4A
-1.2
+1.2
%Vo
Output Temperature Drift
T
A
= 0C70C
40
ppm
Line Regulation
VCCA = 4.75 to 5.25V
I
SW
= 4A
0.10
0.15
%Vo
Load Regulation
I
SW
= 0 to 4A
0.9
1.3
%Vo
Output Ripple, peak-peak
20MHz BW, I
SW
= 4A
15
mV
Cumulative DC Accuracy
3
55
100
mV
Efficiency
I
SW
= 4A
80
%
Output Driver Current
Open Loop
0.5
A
Short Circuit Threshold
Voltage
70
90
100
mV
On Time Pulse Width
4
C
EXT
= 100pF
2
s
FAN5038
PRODUCT SPECIFICATION
5
REV. 1.0.2 7/6/00
Electrical Characteristics--Linear Regulator
(VCCA = 5V, VCCL = 12V, T
A
= 25
C using circuit in Figure 1, unless otherwise noted)
The
denotes specifications which apply over the full ambient operating temperature range.
Notes:
1. When the LIN_EN pin is LOW, the linear regulator output is set with external resistors. When the LIN_EN pin is HIGH, the
linear regulator is disabled and will exhibit no output voltage. Please refer to the Application Section for output voltage
selection information.
2. Setpoint accuracy is the initial output voltage variability under the specified conditions. The matching of the external resistors
will have a major influence on this parameter.
3. Cumulative DC accuracy includes setpoint accuracy, temperature drift, line and load regulation.
4. Crosstalk is defined as the amount of switching noise from the switch-mode regulator that
appears on the output of the linear
regulator when both outputs are in a static load condition.
Electrical Characteristics--Common
(VCCA = 5V, VCCL = 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
Conditions
Min
Typ
Max
Units
Output Voltage, VOL
1
Set by external resistors
1.5
3.6
V
Setpoint Accuracy
2
I
L
=0.5A, using 0.1% resistors
-1.5
+1.5
%
Output Temperature Drift
40
ppm
Line Regulation
VCCL = 11.4V to 12.6V, I
L
= 0.5A
0.1
0.15
%Vo
Load Regulation
I
L
= 0 to 5A
0.7
1
%Vo
Output Noise
0.1 to 20KHz
1
mV
Cumulative DC Accuracy
3
1.7
3
%
Crosstalk
4
I
SW
= 4A
35
mVpp
Short Circuit Comparator
Threshold
40
50
60
mV
Op-amp Output Current
Open Loop
50
70
mA
Parameter
Conditions
Min
Typ
Max
Units
Reference Voltage, VREF
1.485
1.5
1.515
V
VREF PSRR
60
dB
VCCA Supply Current
Independent of load
5
15
mA
VCCP Supply Current
I
SW
= 4A
20
25
mA
VCCL Supply Current
I
L
= 2A
5
mA
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