MIC4782 datasheet(9/23 Pages) MICREL

9 / 23 page

Micrel, Inc.

MIC4782

August 2009

M9999-081709-D

Pin Description

VIN1/VIN2

VIN pins (two pins for VIN1 and two pins for VIN2)

provide power to the source of the internal P-Channel

MOSFET along with the current limiting sensing. VIN1

pins and VIN2 pins are internally connected by anti-

parallel diodes. The VIN operating voltage range is from

3.0V to 6.0V. Due to the high switching speeds, a 10µF

capacitor is recommended close to VIN and the power

ground (PGND) for each pin for bypassing. Please refer

to layout recommendations for more details.

BIAS

The bias (BIAS) provides power to the internal reference

and control sections of the MIC4782. A 10Ω resistor

from VIN to BIAS and a 0.1µF from BIAS to SGND are

required for clean operation.

EN1/EN2

The enable pins (EN1 and EN2) provides a logic level

control of the outputs 1 and 2. In the off state, supply

current of the device is greatly reduced (typically <2µA).

Do not drive the enable pin above the supply voltage.

FB1/FB2

The feedback pins (FB1 and FB2) provides the control

path to control the outputs 1 and 2. A resistor divider

connecting the feedback to the output is used to adjust

the desired output voltage. The output voltage is

calculated as follows:

⎟

⎠

⎞

⎜

⎝

⎛

REF

OUT

where VREF is equal to 0.6V.

A feed-forward capacitor is recommended for most

designs. To reduce current draw, 10KΩ feedback

resistors are recommended from the outputs to the FB

pins (R1 in the equation). The large resistor value and

the parasitic capacitance of the FB pin can cause a high

frequency pole that can reduce the overall system phase

margin. By placing a feed-forward capacitor (across R1),

these effects can be significantly reduced. Feed-forward

capacitance (CFF) can be calculated as follows:

200kHz

CFF

SW1/SW2

The switch pins (SW1 and SW2) connect directly to the

inductor and provide the switching current necessary to

operate in PWM mode. Due to the high speed switching

on these pins, the switch nodes should be routed away

from sensitive nodes. These pins also connect to the

cathodes of the free-wheeling diodes.

PGND1/PGND2

Power ground pins (PGND1 and PGND2) are the ground

paths for the MOSFET drive current. PGND1 pin and

PGND2 pin are internally connected by anti-parallel

diodes. The current loop for the power ground should be

as small as possible and separate from the Signal

ground

(SGND)

loop.

Refer

the

layout

recommendation for more details.

SGND

Signal ground (SGND) is the ground path for the biasing

and control circuitry. The current loop for the signal

ground should be separate from the power ground

(PGND) loop. Refer to the layout recommendation for

more details.

EPAD

The exposed pad on the bottom of the part must be

connected to ground.

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