IRDC3811
TM
SupIRBuck
USER GUIDE FOR IR3811 EVALUATION BOARD
DESCRIPTION
An output over-current protection function is
The IR3811 is a synchronous buck
implemented by sensing the voltage developed
converter, providing a compact, high
across the on-resistance of the synchronous
performance and flexible solution in a small
rectifier MOSFET for optimum cost and
5mmx6mm Power QFN package.
performance.
Key features offered by the IR3811 include,
This user guide contains the schematic and bill
tracking capability for memory application,
of materials for the IR3811 evaluation board.
programmable soft-start ramp, precision
The guide describes operation and use of the
0.6V reference voltage, thermal protection,
evaluation board itself. Detailed application
fixed 600kHz switching frequency requiring
information for IR3811 is available in the
no external component, input under-voltage
IR3811 data sheet.
lockout for proper start-up, and pre-bias
start-up.
BOARD FEATURES
V = +12V (13.2V Max)
in
Tracking Input
V = 0.75V @ 0- 7A V :0.6V
out p
L= 0.6uH
C = 3x10uF (ceramic 1206) + 330uF (electrolytic)
in
C = 6x22uF (ceramic 0805)
out
Rev 0.1
1
01/07/2008IRDC3811
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 7A 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.
IR3811 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). These inputs are
connected on the board with a zero ohm resistor (R15). Separate supplies can be applied to these inputs.
Vcc input cannot be connected unless R15 is removed. Vcc input should be a well regulated 5V-12V supply
and it would be connected to Vcc+ and Vcc-.
Vp pin is connected to the internal reference (Vref) via R14 as the default configuration. External input can
be applied to Vp. For tacking applications, R14 should be removed, R17 should be inserted, and the
external tracking source should be applied between Vp_Ext and Agnd. The value of R17 and R28 can be
selected to provide the desired ratio between the output voltage and the tracking input. For proper operation
of IR3811, the voltage at Vp pin should be kept between 0.2V to 1.0V.
Table I. Connections
Connection Signal Name
VIN+ V (+12V)
in
VIN- Ground of V
in
Vcc+ Optional Vcc input
Vcc- Ground for optional Vcc input
VOUT- Ground of V
out
VOUT+ V (+1.8V)
out
Vp_Ext Optional Tracking input
Agnd Analog (Signal) Ground
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3811 SupIRBuck and all of the
passive components are mounted on the top side of the board.
Power supply decoupling capacitors, the charge-pump capacitor and feedback components are located
close to IR3811. 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.
Rev 0.1
2
01/07/2008