MIC2587 datasheet(4/16 Pages) MICREL

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Micrel

MIC2587/MIC2587R

October 2004

M9999-102204

(408) 955-1690

Pin Description

Pin Number

Pin Name

Pin Function

GATE

Gate Drive Output: This pin is the output of an internal charge pump connected to the gate

of an external, N-channel power MOSFET. The charge pump has been designed to provide

a minimum gate drive (

∆V

GATE = VGATE - VCC) of +7.5V over the input supply’s full operating

range. When the ON pin voltage is higher than the VONH threshold, a 16µA current source

(IGATEON) charges the GATE pin.

When in current limit, the output voltage at the GATE pin is adjusted so that the voltage

across the external sense resistor is held equal to VTRIP while the capacitor connected to the

TIMER pin charges. If the current limit condition goes away before the TIMER pin voltage

rises above the VTIMERH threshold, then steady-state operation resumes.

The GATE output pin is shut down whenever: (1) the input supply voltage is lower than the

VUVL threshold, (2) the ON pin voltage is lower than the VONL threshold, (3) the TIMER pin

voltage is higher than the VTIMERH threshold, or (4) the difference between the VCC and

SENSE pins is greater than VTRIP while the TIMER pin is grounded. For cases (3) and (4) –

overcurrent fault conditions – the GATE is immediately pulled to ground by IGATEFLT, a 30mA

(minimum) pull-down current.

SENSE

Circuit Breaker Sense Input:

This pin is the (-) Kelvin sense connection for the output

supply rail. A low-valued resistor (RSENSE) between this pin and the VCC pin sets the circuit

breaker’s current limit trip point. When the current limit detector circuit is enabled (as well as

the current limit timer), while the FB pin voltage remains higher than 1V, the voltage across

the sense resistor (VCC-VSENSE) will be regulated to VTRIP (47mV, typically) to maintain a

constant current into the load. When the FB pin voltage is less than

≅0.5V, the voltage

across the sense resistor decreases linearly to a minimum of 12mV (typical) when the FB

pin voltage is at 0V.

To disable the circuit breaker (and defeat all current limit protections), the SENSE pin and

the VCC pin can be tied together.

VCC

Positive Supply Voltage Input: This pin is the (+) Kelvin sense connection for the output

supply rail. The nominal operating voltage range for the MIC2587 and the MIC2587R is

+10V to +80V, and VCC can withstand input transients up to +100V.

An undervoltage

lockout circuit holds the GATE pin low whenever the supply voltage to the MIC2587 and the

MIC2587R is less than the VUVH threshold.

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