MP2905- 3V to 28V INPUT, HYSTERETIC SYNCHRONOUS STEP-DOWN CONTROLLER

MP2905 Rev. 0.91

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4

4/18/2011

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PIN FUNCTIONS

Pin#

Name

Description

1

FB

Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a

resistive voltage divider from the output voltage. The feedback reference voltage is

0.59V. See Setting the Output Voltage.

2

SS

Soft-start Control Input. SS controls the soft-start period. Connect a capacitor from SS to

GND to set the soft-start period.

A 0.01uF external capacitor sets the soft-start period to 4ms with an internal 84Kohm

resistor.

An internal 250nA current sink in hiccup mode gives approximately 10% duty cycle

during fault conditions.

3

REF

Internal 5V LDO output. Bypass REF to GND with a 4.7uF or greater capacitor.

4

GND

Ground. Connect the exposed pad to pin 4

5

LG

Low-side Gate-Drive output. Drive the synchronous-rectifier MOSFET.

Connect this pin to the gate of the synchronous MOSFET.

6

BST

High-Side Gate Drive Boost Input. BST supplies the drive for the high-side N-channel

MOSFET switching. Connect a 0.1uF or greater capacitor from SW to BST to power the

high side switch.

MP2905 contains an internal BST regulator, so external schottky from REF to BST is not

necessary.

7

SW

Switch Output. SW is the switching node that supplies power to the output. Connect the

output LC filter from SW to the output load. Note that a capacitor is required from SW to

BST to power the high-side switch.

8

HG

High-side gate-drive output. Drive the high-side MOSFET. Connect this pin to the gate of

the high-side MOSFET

9

IN

Power Input. IN supplies the power to the IC, as well as the step-down converter

switches. Drive IN with a 3V to 28V power source. Bypass IN to GND with a suitably

large capacitor to eliminate noise on the input to the IC. See Setting the Input Capacitor.

10

ILIM

Current-limit threshold Set pin. A appropriate resistor should be connected between this

pin and the drain of high-side MOSFET (IN). An internal 50uA current sink sets a voltage

drop in the resistor. The voltage drop compares to high-side MOSFET voltage drop (Vds)

to set the peak current-limit threshold.