IRDC3894-P1V2

12/22/2011

2

CONNECTIONS AND OPERATING INSTRUCTIONS

Table I. Connections

Connection

Signal Name

VIN+

Vin (+12V)

VIN-

Ground of Vin

Vout+

Vout(+1.2V)

Vout-

Ground for Vout

Vcc+

Vcc/ LDO_out Pin

Vcc-

Ground for Vcc input

Enable

Enable

PGood

Power Good Signal

Gnd

Analog ground

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.

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.