5
Introduction
The ISL6119 is a fully independent dual channel overcurrent
(OC) fault protection IC for the +2.5V to +5.5V environment.
Each ISL6119 incorporates in a single 8 lead SOIC package
two 80mW N-channel MOSFET power switches for power
control. Independent enabling inputs and fault reporting
outputs compatible with 3V and 5V logic allows for external
control and monitoring. This device features internal current
monitoring, accurate current limiting, integrated power
switches and current limited timed delay to latch-off for
system protection. See Figure 1 for typical operational
waveforms including both under and overcurrent situations.
Key Feature Description and Operation
UV Lock Out
The ISL6119 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 ISL6119 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 ISL6119 has integrated current sensing on the power
MOSFET that allows for rapid control of OC events. Once an
OC is detected the ISL6119 goes into its current regulation
(CR) control mode. The ISL6119 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
overcurrent 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 ISL6119 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 ISL6119 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 ISL6119 has latched off, and the fault has
asserted and, the enable is not deasserted but the OC
condition still exists, the ISL6119 unlike other IC devices
does not send to the controller a continuous string of fault
pulses. The ISL6119’s single fault signal is sent at the time of
latch-off unlike other devices.
Slow And Fast Shutdown
The ISL6119 has two shutdown modes. When turned off with
a load current less than the current regulation (CR) level the
ISL6119 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 ISL6119 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 ISL6119 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
ISL6119
