ISL8200MMREP datasheet(15/24 Pages) RENESAS

15 / 24 page

ISL8200MM

FN7690 Rev 2.00

Page 15 of 24

Mar 15, 2013

Fault Handshake

In a multi-module system, with the EN pins wired OR’ed together,

all modules can immediately turn off, at one time, when a fault

condition occurs in one or more modules. A fault would pull the

EN pin low, disabling all the modules and would not create

current bounce. Thus, no single channel would be over stressed

when a fault occurs.

Since the EN pins are pulled down under fault conditions, the

pull-up resistor (RUP) should be scaled to sink no more than 5mA

current from EN pin. Essentially, the EN pins cannot be directly

connected to VCC.

Soft-Start

The ISL8200MMREP has an internal digital pre-charged

soft-start circuitry, which has a rise time inversely proportional to

the switching frequency and is determined by a digital counter

that increments with every pulse of the phase clock. The full

soft-start time from 0V to 0.6V can be estimated by Equation 5.

tSS

2560

fSW

-------------

(EQ. 5)

VOUT TARGET VOLTAGE

0.0V

tSS

2560

fSW

-------------

FIRST PWM PULSE

-100mV

tSS_DLY

384

FSW

------------



FIGURE 22. SOFT-START WITH VOUT = 0V

SS Settling at VREF + 100mV

INIT. VOUT

VOUT TARGET VOLTAGE

FIRST PWM PULSE

-100mV

SS Settling at VREF + 100mV

FIGURE 23. SOFT-START WITH VOUT < TARGET VOLTAGE

OV = 113%

VOUT TARGET VOLTAGE

FIRST PWM PULSE

FIGURE 24. SOFT-START WITH VOUT BELOW OV BUT ABOVE FINAL

TARGET VOLTAGE

FIGURE 25. SIMPLIFIED ENABLE AND VOLTAGE FEED-FORWARD CIRCUIT

0.8V

IEN_HYS = 30μA

RUP

RDOWN

SOFT-START

RDOWN

RUP V

EN_REF

VEN_FTH VEN_REF

–

---------------------------------------------------------------

VEN_FTH VEN_RTH VEN_HYS

–

VIN

GRAMP = 1.25

LIMITER

SAWTOOTH

AMPLITUDE

D RAMP

LIMIT(VCC_FF GRAMP, VCC - 1.4V - VRAMP_OFFSET

(DVRAMP)

OV, OT, OC, AND PLL LOCKING FAULTS

RUP

VEN_HYS

IEN_HYS

-----------------------------

SYSTEM DELAY

VCC_FF

0.8V

VRAMP_OFFSET = 1.0V

VCC - 1.4V

LOWER LIMIT

UPPER LIMIT

(RAMP OFFSET)

384 CLOCK

CYCLES

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