MP3908 – HIGH EFFICIENCY BOOST CONTROLLER

MP3908 Rev.0.9

www.MonolithicPower.com

3

8/29/2008

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Parameter

Symbol Condition

Min

Typ

Max

Units

ISENSE Bias Current

Current flowing out of part

50

nA

Enable On Threshold

High-to-Low

1.15

1.25

1.35

V

Enable Hysteresis

50

mV

Soft Start Current

4

µA

PIN FUNCTIONS

Pin #

Name

Description

1

CSS

Capacitor Soft Start. A charging current of 5µA is enabled when the ENABLE pin is

taken above 1.2V. The rise time of the capacitor allows output current soft start. Full

output current is allowed when the voltage is above 2.7V.

2

ENABLE

This pin serves two functions. Below 0.6V, the part is in sleep mood, drawing 10µA

(typ). The second threshold of 1.2V can be used as a precise under-voltage lock out

(UVLO) and enables full operation..

3

COMP

Compensation.

4

FB

Feedback forces this pin voltage to the 0.8V internal reference potential. Do not allow

this pin to rise above 1.2V in the application.

5

RDELAY

External resistor determines delay between the Synchronous Gate Drive pin going low

to the Main Gate drive going high.

6

ISENSE

Current Sense. Do not connect this pin directly to the drain of the external MOSFET if

the voltage swing exceeds 27V in the particular application. During normal operation,

this pin will sense the voltage across the external MOSFET or sense resistor if one is

used, limiting the peak inductor current on a cycle-by-cycle basis.

7

GND

Ground.

8

VCC

Input Supply. Decouple this pin as close as possible to the GND pin.

9

MAIN GATE This pin drives the external MAIN MOSFET device.

10

SYNC GATE

This pin drives the external SYNCHRONOUS MOSFET device. The Sync Gate is

disabled at the end of switching period if Main Gate is not turned on the next cycle.