HIP6019B datasheet(8/15 Pages) INTERSIL

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indicates when CSS is fully charged (UP signal), such that an

under-voltage event on either linear output (FB3 or FB4) is

ignored until after the soft-start interval (approximately T3 in

Figure 6). At start-up, this allows VOUT3 and VOUT4 to slew

up over increased time intervals, without generating a fault.

Cycling the bias input voltage (+12VIN on the VCC pin) off

then on resets the counter and the fault latch.

Over-Voltage Protection

During operation, a short on the upper MOSFET (Q1)

causes VOUT1 to increase. When the output exceeds the

over-voltage threshold of 115% of DACOUT, the over-

voltage comparator trips to set the fault latch and turns Q2

on as required in order to regulate VOUT1 to 1.15 x

DACOUT. This blows the input fuse and reduces VOUT1.

The fault latch raises the FAULT/RT pin close to VCC

potential.

A separate over-voltage circuit provides protection during

the initial application of power. For voltages on the VCC pin

below the power-on reset (and above ~4V), VOUT1 is

monitored for voltages exceeding 1.26V. Should VSEN1

exceed this level, the lower MOSFET (Q2) is driven on, as

needed to regulate VOUT1 to 1.26V.

Over-Current Protection

All outputs are protected against excessive over-currents.

Both PWM controllers use the upper MOSFET’s

on-resistance, rDS(ON) to monitor the current for protection

against shorted outputs. The linear regulator monitors the

current of the integrated power device and signals an over-

current condition for currents in excess of 230mA.

Additionally, both the linear regulator and the linear

controller monitor FB3 and FB4 for under-voltage to protect

against excessive currents.

Figures 8 and 9 illustrate the over-current protection with an

overload on OUT2. The overload is applied at T0 and the

current increases through the output inductor (LOUT2). At time

T1, the OVER-CURRENT2 comparator trips when the voltage

across Q3 (ID • rDS(ON)) exceeds the level programmed by

ROCSET. This inhibits all outputs, discharges the soft-start

capacitor (CSS) with a 11µA current sink, and increments the

counter. CSS recharges at T2 and initiates a soft-start cycle

with the error amplifiers clamped by soft-start. With OUT2 still

overloaded, the inductor current increases to trip the over-

current comparator. Again, this inhibits all outputs, but the

soft-start voltage continues increasing to 4V before

discharging. The counter increments to 2. The soft-start cycle

repeats at T3 and trips the over-current comparator. The SS

pin voltage increases to 4V at T4 and the counter increments to

3. This sets the fault latch to disable the converter. The fault is

reported on the FAULT/RT pin.

The PWM1 controller and the linear regulator operate in the

same way as PWM2 to over-current faults. Additionally, the

linear regulator and linear controller monitor the feedback

pins for an under-voltage. Should excessive currents cause

FB3 or FB4 to fall below the linear under-voltage threshold,

the LUV signal sets the over-current latch if CSS is fully

charged. Blanking the LUV signal during the CSS charge

interval allows the linear outputs to build above the under-

FAULT

LATCH

POR

COUNTER

OC1

OC2

LUV

0.15V

VCC

FAULT

FIGURE 7. FAULT LOGIC - SIMPLIFIED SCHEMATIC

OVER

CURRENT

LATCH

INHIBIT

FIGURE 8. OVER-CURRENT OPERATION

TIME

10V

FAULT

REPORTED

COUNT

= 1

COUNT

= 2

COUNT

= 3

OVERLOAD

APPLIED

HIP6019B

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