ISL6436 Datasheet, PDF (5/12 Pages) Intersil Corporation – USB Dual Port Power Supply Controller

ISL6436
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.
ON _OFF
ENABLE
FAULT
VOUT
LATCH-OFF SET
RESET BY
ENABLE
CURRENT
REGULATION
SETTLING TIME
(1.4ms)
OVER CURRENT
IOUT
1A CURRENT
LIMIT
12ms CURRENT REGULATION PERIOD
FIGURE 1. TYPICAL OPERATIONAL WAVEFORMS
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