MIC23031 datasheet(10/17 Pages) MICREL

10 / 17 page

Micrel Inc.

MIC23031

May 2008

M9999-051608-A

Functional Description

VIN

The input supply (VIN) provides power to the internal

MOSFETs for the switch mode regulator along with the

internal control circuitry. The VIN operating range is 2.7V

to 5.5V so an input capacitor, with a minimum voltage

rating of 6.3V, is recommended. Due to the high

switching speed, a minimum 2.2µF bypass capacitor

placed close to VIN and the power ground (PGND) pin is

required. Refer to the layout recommendations for

details.

A logic high signal on the enable pin activates the output

voltage of the device. A logic low signal on the enable

pin deactivates the output and reduces supply current to

0.01µA. MIC23031 features built-in soft-start circuitry

that reduces in-rush current and prevents the output

voltage from overshooting at start up. Do not leave

floating.

The switch (SW) connects directly to one end of the

inductor and provides the current path during switching

cycles. The other end of the inductor is connected to the

load, SNS pin and output capacitor. Due to the high

speed switching on this pin, the switch node should be

routed away from sensitive nodes whenever possible.

SNS

The sense (SNS) pin is connected to the output of the

device to provide feedback to the control circuitry. The

SNS connection should be placed close to the output

capacitor. Refer to the layout recommendations for more

details.

AGND (Fixed Output Only)

The analog ground (AGND) 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 recommendations for

more details.

FB (Adjustable Output Only)

The feedback pin (FB) allows the regulated output

voltage to be set by applying an external resistor

network. The internal reference voltage is 0.62V and the

recommended value of R2 is 200k

Ω. The output voltage

is calculated from the equation below.

⎟

⎠

⎞

⎜

⎝

⎛

kΩ

200

VOUT

SNS

GND

MIC23031

VIN

VOUT

GND

Figure 1. MIC23031-AYMT Schematic

PGND / GND

The power ground pin is the ground path for the high

current in PWM mode. The current loop for the power

ground should be as small as possible and separate

from the analog ground (AGND) loop as applicable.

Refer to the layout recommendations for more details.

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