IRDC3894-P1V2
SupIRBuck
TM
USER GUIDE FOR IR3894 EVALUATION BOARD
1.2Vout
DESCRIPTION
The IR3894 is a synchronous buck
converter, providing a compact, high
performance and flexible solution in a small
5mm X 6 mm Power QFN package.
Key features offered by the IR3894 include
internal Digital Soft Start/Soft Stop, precision
0.5Vreference voltage, Power Good
,
thermal protection, programmable switching
frequency, Enable input, input under-voltage
lockout for proper start-up, enhanced line/
load regulation with feed forward, external
frequency synchronization with smooth
clocking, smart internal LDO and pre-bias
start-up.
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 and the current limit is thermally
compensated.
This user guide contains the schematic and bill
of materials for the IR3894 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3894 is available in the
IR3894 data sheet.
BOARD FEATURES
•
V
in
= +12V (+ 13.2V Max)
•V
out
= +1.2V @ 0- 12A
•
F
s
=600kHz
•
L= 0.51uH
•
C
in
= 4x10uF (ceramic 1206) + 1X330uF (electrolytic)
•
C
out
=8x22uF (ceramic 0805)
12/22/2011
1
IRDC3894-P1V2
CONNECTIONS AND OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 12A load should
be connected to VOUT+ and VOUT-. The input and output connections of the board are listed in Table I.
IR3894 has only one input supply and internal LDO generates Vcc from Vin. If operation with external Vcc
is required, then R15 can be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin
and Vcc/LDOout pins should be shorted together for external Vcc operation (use zero ohm resistor for R29).
The output can track voltage at the Vp pin. For this purpose, Vref pin is to be connected to ground (use zero
ohm resistor for R21). The value of R14 and R28 can be selected to provide the desired tracking ratio
between output voltage and the tracking input.
Table I. Connections
Connection
VIN+
VIN-
Vout+
Vout-
Vcc+
Vcc-
Enable
PGood
Gnd
Signal Name
Vin (+12V)
Ground of Vin
Vout(+1.2V)
Ground for Vout
Vcc/ LDO_out Pin
Ground for Vcc input
Enable
Power Good Signal
Analog ground
LAYOUT
The PCB is a 4-layer board (2.23”x2”) using FR4 material. All layers use 2 Oz. copper. The PCB
thickness is 0.062”. The IR3894 and other major power components are mounted on the top side of the
board.
Power supply decoupling capacitors, the bootstrap capacitor and feedback components are located
close to IR3894. The feedback resistors are connected to the output at the point of regulation and are
located close to the SupIRBuck IC. To improve efficiency, the circuit board is designed to minimize the
length of the on-board power ground current path.
12/22/2011
2
Programming Basics
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