IRDC3831
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IR3831 EVALUATION BOARD
The IR3831 is a synchronous buck
converter, providing a compact, high
performance and flexible solution in a small
5mmx6mm Power QFN package.
Key features offered by the IR3831 include
programmable soft-start ramp, Power Good
,
thermal protection, programmable switching
frequency, tracking input, enable input, input
under-voltage lockout for proper start-up,
and pre-bias start-up.
An output over-current protection function is
implemented by sensing the voltage developed
across the on-resistance of the synchronous
rectifier MOSFET for optimum cost and
performance.
This user guide contains the schematic and bill
of materials for the IR3831 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3831 is available in the
IR3831 data sheet.
BOARD FEATURES
•
V
in
= +12V (13.2V Max)
• V
cc
= +5V (5.5V Max)
•
V
out
= +0.75V @ 0- ±8A
• F
s
= 400kHz
•
L = 0.68uH
•
C
in
= 3x10uF (ceramic 1206) + 330uF (electrolytic)
•
C
out
= 8x22uF (ceramic 0805)
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IRDC3831
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum ±8A load should be
connected to VOUT+ and VOUT-. The connection diagram is shown in Fig. 1 and inputs and outputs of the
board are listed in Table I.
IR3831 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). Separate supplies
should be applied to these inputs. Vcc input should be a well regulated 4.5V-5.5V supply and it would be
connected to Vcc+ and Vcc-.
If single 12V application is required, connect R7 ( zero Ohm resistor) which enables the on board bias
regulator (see schematic). In this case there is no need of external Vcc supply.
The output tracks VDDQ input. The value of R14 and R28 can be selected to provide the desired ratio
between the output voltage and the tracking input.
For proper operation of IR3831, the voltage at Vp pin
should not exceed Vcc.
Table I. Connections
Connection
VIN+
VIN-
Vcc+
Vcc-
VOUT-
VOUT+
Enable
V
DDQ
PGood
Signal Name
V
in
(+12V)
Ground of V
in
Vcc input
Ground for Vcc input
Ground of V
out
V
out
(+0.75V)
Enable
Tracking Input
Power Good Signal
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3831 SupIRBuck and all of the
passive components are mounted on the top side of the board.
Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located
close to IR3831. The feedback resistors are connected to the output voltage at the point of regulation
and are located close to the SupIRBuck. To improve efficiency, the circuit board is designed to
minimize the length of the on-board power ground current path.
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IRDC3831
Connection Diagram
Vin
GND
Enable
Vp
GND
VDDQ
AGND
Vo
PGood
SS
Vcc
GND
Fig. 1: Connection diagram of IR383x evaluation boards
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IRDC3831
Fig. 2: Board layout, top overlay
Fig. 3: Board layout, bottom overlay
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IRDC3831
AGND
Plane
PGND
Plane
Single point
connection
between AGND
and PGND.
Fig. 4: Board layout, mid-layer I
Fig. 5: Board layout, mid-layer II
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