International Rectifier IR3821 User Manual

IRDC3821

SupIRBuck

TM

USER GUIDE FOR IR3821 EVALUATION BOARD

DESCRIPTION

The IR3821 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 IR3821 include
programmable soft-start ramp, precision

0.6V reference voltage, programmable

Power Good
600kHz switching frequency requiring no
external component, input under-voltage
lockout for proper start-up, and pre-bias
start-up.

, thermal protection, fixed

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 IR3821 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3821 is available in the
IR3821 data sheet.

BOARD FEATURES

Vin= +12V (13.2V Max)

•

• V

= +1.8V @ 0- 7A

out

• L=1.0uH

• C

=3x10uF (ceramic 1206) + 330uF (electrolytic)

in

• C

=6x22uF (ceramic 0805)

out

Rev 0.1
01/07/2008

1

IRDC3821

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.

IR3821 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.

and it would be connected to Vcc+ and Vcc-.

Table I. Connections

Signal NameConnection

Vcc input should be a well regulated 5V-12V supply

(+12V)VIN+

V

in

VIN-

VOUT-

Ground of V

Optional Vcc inputVcc+

Ground for Optional Vcc inputVcc-

Ground of V

V

(+1.8V)VOUT+

out

Power Good SignalP_Good

in

out

LAYOUT

The PCB is a 4-layer board. All of layers are 2Oz. copper. The IR3821 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 IR3821. The feedback resistors are connected to the output voltage at the point of regulation
and are located close to SupIRBuck.

To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground
current path.

Rev 0.1
01/07/2008

2

Connection Diagram

IRDC3821

V

CC+

GROUND

Vin= +12v

GROUND

GROUND

Fig. 1: Connection diagram of IR3821 evaluation board

Rev 0.1
01/07/2008

P

Good

V

OUT

= +1.8v

3

IRDC3821

Fig. 2: Board layout, top overlay

Fig. 3: Board layout, bottom overlay (rear view)

Rev 0.1
01/07/2008

4

IRDC3821

AGND
Plain

Single point
connection
between AGND
and PGND.

Fig. 4: Board layout, mid-layer I

PGND
Plain

Fig. 5: Board layout, mid-layer II

Rev 0.1
01/07/2008

5