MIC2586 datasheet(4/17 Pages) MICREL

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Micrel

MIC2586/MIC2586R

October 2004

M9999-102204

(408) 955-1690

Pin Description

Pin Number

Pin Name

Pin Function

PGTIMER

Power-is-Good Delay Timer: A capacitor (CPG) connected from this pin to GND

sets a delay from PWRGD1 to PWRGD2 (tPG(1-2)) and from PWRGD1 to

PWRGD3 (tPG(1-3)). An internal current source (ICPG) is used to charge CPG only

after PWRGD1 has been asserted. The same description applies to the active-

LOW (-2) output signals.

PWRGD3

(MIC2586-1)

(MIC2586R-1)

Active-HIGH

/PWRGD3

(MIC2586-2)

(MIC2586R-2)

Active-LOW

Power-is-Good Output 3 (PWRGD3 or /PWRGD3), Open-drain Output: For the

(-1) option, this output signal is asserted when the following is true: PWRGD1 =

Asserted AND the PWRGD1-to-PWRGD3 delay (tPG(1-3)) has elapsed, where

tPG(1-3) is the time delay programmed by the capacitor (CPG) connected to the

PGTIMER pin. Once PWRGD1 is asserted, an internal current source (ICPG)

begins to charge CPG. When the voltage on CPG crosses the VPG3 threshold

(typically, 1.25V), PWRGD3 is asserted. The same description above applies to

the (-2) option. For further information, refer to the PWRGD1 and PGTIMER pin

descriptions.

To use this signal as a logic control in low-voltage dc-dc conversion applications,

an external pull-up resistor between this pin and the logic supply voltage is

recommended, unless an internal pull-up impedance is provided by the dc-dc

module or other device (load).

TIMER

Current Limit Response Timer:

A capacitor connected from this pin to GND

provides overcurrent filtering to prevent nuisance “tripping” of the circuit breaker

by setting the time (tFLT) for which the controller is allowed to remain in current

limit.

Once the MIC2586 circuit breaker trips, the output latches off.

Under

normal (steady-state) operation, the TIMER pin is held to GND by an internal

3.5

µA current source (I

TIMERDN).

When the voltage across the external sense

resistor exceeds the VTRIP threshold, an internal 65µA current source (ITIMERUP) is

activated to charge the capacitor connected to the TIMER pin. When the TIMER

pin voltage reaches the VTIMERH threshold, the circuit breaker is tripped pulling

the GATE pin low, the ITIMERUP current source is disabled, and the TIMER pin

capacitor is discharged by the ITIMERDN current source. When the voltage at the

TIMER pin is less than 0.5V, the MIC2586 can be restarted by toggling the ON

pin LOW then HIGH.

For the MIC2586R, the capacitor connected to the TIMER pin sets the period of

auto-retry where the duty cycle is fixed at a nominal 5%.

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.

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