5

UV Lock Out

The ISL6436 undervoltage lockout feature prevents

functionality of the device unless the correct ENABLE state and

VIN > 2.5V are present.

Soft Start

A constant 500nA current source ramps up the switch’s gate

causing a voltage follower effect on the output voltage. This

provides a soft start turn-on eliminating bus voltage drooping

caused by in-rush current charging heavy load capacitances.

Rising and falling outputs are current limited voltage ramps so

that both the inrush current and voltage slew rate are limited,

independent of load. This reduces supply droop due to surge

and also eliminates the need for EMI filters necessary on other

IC products.

Fault Blanking On Start-Up

During initial turn-on the ISL6436 prevents nuisance faults

being reported to the system controller by blanking the fault

signal for 12ms. This blanking eliminates the need for external

RC filters necessary for other vendor products that assert a

fault signal upon initial turn-on into a temporary high current

condition. See Figures 10 through 12 for waveform examples.

Current Regulation

The ISL6436 has integrated current sensing on the power

MOSFET that allows for rapid control of OC events. Once an

OC is detected the ISL6436 goes into its current regulation

(CR) control mode. The ISL6436 CR level is set to a nominal

1A. This current regulation is

±25% over the full operating

temperature and voltage bias range. See Figures 4 and 5 for

illustrative curves. The speed of this control is inversely related

to the magnitude of the OC fault. Thus a hard over current is

more quickly controlled than a marginal OC condition. See

Figure 6 for waveforms illustrating this and Figure 7 for an

accompanying graph.

Over Temperature Shutdown

Although the ISL6436 has a thermal shutdown feature,

because of the 12ms timed shutdown this will only be invoked

in extremely high ambient temperatures.

Latch-Off Time Delay

The primary function of any OC protection device is to quickly

isolate the voltage bus from a faulty load. Unlike many other

IC products that sense the IC thermal condition (the monitored

IC junction temperature depends on a number of factors the

most important of which are power dissipation of the faulted

and adjacent switches and package temp) to isolate a faulty

load, the ISL6436 uses an internal 12ms timer that starts upon

OC detection. Once an OC condition is detected the

appropriate output is current limited for a maximum of 12ms to

allow transient conditions to pass before latch-off. This time to

latch-off is independent of device thermal or adjacent switch

condition. See Figure 18 for waveforms illustrating

independent latch-off.

If, after the ISL6436 has latched off, and the fault has asserted

and, the enable is not deasserted but the OC condition still

exists, the ISL6436 unlike other IC devices does not send to

the controller a continuous string of fault pulses. The

ISL6436’s single fault signal is sent at the time of latch-off

unlike other devices.

Slow And Fast Shutdown

The ISL6436 has two shutdown modes. When turned off

with a load current less than the current regulation (CR)

level the ISL6436 shuts down in a controlled manner using

a 500nA constant current source controlled ramp. When

latched off due to CR and the timer has expired, the

ISL6436 quickly pulls down the output thereby quickly

removing the faulted load from the voltage bus. See

Figures 8 and 9 for waveforms of each mode.

Active Output Pulldown

Another unique ISL6436 feature is the active pull down on

the outputs to 300mV above GND when the device is

disabled. Competitors’ parts’ switch leakage causes the

output voltage to drift up to VIN voltage even when the part

is supposed to be disabled.

OFF

ON

FAULT

LATCH-OFF SET

RESET BY

ENABLE

VOUT

CURRENT

REGULATION

SETTLING TIME

(1.4ms)

OVER CURRENT

12ms CURRENT REGULATION PERIOD

1A CURRENT

LIMIT

ENABLE

IOUT

FIGURE 1. TYPICAL OPERATIONAL WAVEFORMS

ISL6436