IRDC3842
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IR3842 EVALUATION BOARD
The IR3842 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 IR3842 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 IR3842 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3842 is available in the
IR3842 data sheet.
BOARD FEATURES
•
V
in
= +12V (13.2V Max)
•
V
cc
=+5V (5.5V Max)
•
V
out
= +1.8V @ 0- 4A
•
F
s
=600kHz
•
L= 1.5uH
•
C
in
= 2x10uF (ceramic 1206) + 330uF (electrolytic)
•
C
out
= 4x22uF (ceramic 0805)
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IRDC3842
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 4A 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.
IR3842 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 can track a sequencing input at the start-up.
For sequencing application, R16 should be
removed and the external sequencing source should be applied between Seq. and Agnd.
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 IR3842, the voltage at Seq. pin should not exceed Vcc.
Table I. Connections
Connection
VIN+
VIN-
Vcc+
Vcc-
VOUT-
VOUT+
Enable
Seq.
P_Good
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. The IR3842 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 IR3842. 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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IRDC3842
Connection Diagram
Vin
GND
Enable
GND
Seq
AGND
Vo
PGood
SS
Vcc
GND
Fig. 1: Connection diagram of IR384x evaluation boards
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IRDC3842
Fig. 2: Board layout, top overlay
Fig. 3: Board layout, bottom overlay (rear view)
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IRDC3842
PGND
Plane
Single point
connection
between AGND
and PGND.
AGND
Plane
Fig. 4: Board layout, mid-layer I.
Fig. 5: Board layout, mid-layer II.
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