IRDC3843A
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IR3843A EVALUATION BOARD
Double Sided PCB
The IR3843A 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 IR3843A include
programmable soft-start ramp, precision
0.7V reference voltage, Power Good
,
thermal protection, programmable switching
frequency, Sequence 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 IR3843A evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3843A is available in the
IR3843A data sheet.
BOARD FEATURES
•
V
in
= +12V (13.2V Max)
•
V
cc
=+5V (5.5V Max)
•
V
out
= +1.8V @ 0- 3A
•
F
s
=600kHz
•
L= 2.2uH
•
C
in
= 1x10uF (ceramic 1206)
•
C
out
= 3x22uF (ceramic 0805)
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IRDC3843A
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 3A 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.
IR3843A 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-.
Table I. Connections
Connection
VIN+
VIN-
Vcc+
Vcc-
VOUT-
VOUT+
Enable
Seq.
PGood
Signal Name
V
in
(+12V)
Ground of V
in
Vcc input
Ground for Vcc input
Ground of V
out
V
out
(+1.8V)
Enable
Sequence Input
Power Good Signal
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper.
It
is a double sided board with components
mounted on both sides.
Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located
close to IR3843A. 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.
02/09/10
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