4
Introduction
The ISL6118 is a fully independent dual channel overcurrent
(OC) fault protection IC for the +2.5V to +5.5V environment.
Each ISL6118 incorporates in a single 8-lead SOIC package
two 80mW N-channel MOSFET power switches for power
control. See Figure 2 for integrated FET on resistance curves.
Independent enabling inputs and fault reporting outputs
compatible with 3V and 5V logic allow 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.
Key Feature Description and Operation
UV Lockout
The ISL6118 undervoltage (UVLO) lockout 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 and eliminates bus voltage
drooping caused by inrush 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
external EMI filters necessary on other IC products. See
Figure 3 for soft start waveforms.
Fault Blanking on Start-Up
During initial turn-on the ISL6118 prevents nuisance faults
from 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 vendors’ products.
Current Regulation
The ISL6118 has integrated current sensing on the power
MOSFETs that allows for rapid control of OC events. Once
an OC condition is detected the ISL6118 goes into its current
regulation (CR) control mode. The ISL6118 CR level is set to
a nominal 0.6A and is regulated to within ±25% over full
temperature, bias voltage range and OC magnitude. The
speed of this control is proportional to the level of OC. Thus
a hard OC is more quickly controlled than a marginal
condition. See Figures 4 through 7 for current regulation
performance curves and waveforms.
Latch-Off Time Delay
The primary function of any OC protection device is to
quickly isolate the voltage bus from a faulty load. Unlike
other manufacturers’ IC products that sense the IC thermal
condition to isolate a faulty load, the ISL6118 uses an
internal 12ms timer that starts upon OC detection. Once an
OC condition is detected, the appropriate output is current
limited for 12ms to allow transient conditions to pass before
latch-off. The time to latch-off is independent of the device’s
thermal or adjacent switch’s electrical condition. See Figure
10 for waveforms illustrating independent latch-off.
If, after the ISL6118 has latched off, and the fault has asserted
and the enable is not deasserted but the OC condition still
exists, the ISL6118 (unlike other IC devices) does not send to
the controller a continuous string of fault pulses. The
ISL6118’s single fault signal is sent at the time of latch off.
Slow and Fast Shutdown
The ISL6118 has two shutdown modes. When disabled with
a load current less than the current regulation (CR) level the
ISL6118 shuts down in a controlled manner using a 500nA
constant current source controlled ramp. When disabled
during CR or if the timer has expired the ISL6118 quickly
pulls down the output thereby quickly removing the faulted
load from the voltage bus. See Figures 8 and 9 for illustrative
waveforms of each shutdown mode.
Over Temperature Shutdown
Although the ISL6118 has a thermal shutdown feature,
because of the 12ms timed shutdown this will only be
invoked in extremely high ambient temperatures.
Active Output Pulldown
Another unique ISL6118 feature is the active pull down on the
outputs to 300mV above GND when the device is disabled.
Figure 1 illustrates the ISL6118 operational waveforms,
showing the relationships between the various I/O signals
during typical and faulted conditions. It also graphically
highlights many of the terms and modes of operation
referred to in this data sheet.
Using the ISL6118EVAL1 Platform
General and Biasing Information
The ISL6118EVAL1 platform, Figure 14, allows evaluation of
the ISL6118 dual power supply control IC and comparison
against a suitably sized PPTC component.
The evaluation platform is biased and monitored through
numerous test points (TP#). See Table 1 for test point
assignments and descriptions.
TABLE 1. ISL6118EVAL1 TEST POINT ASSIGNMENTS
TP # DESCRIPTION
TP1 Eval Board and IC GND
TP2 Eval Board +3.3V Bias
TP3 Enable Switch 1
TP4 Enable Switch 2
TP5 Switch 2 Fault
TP6 Switch Out 2
TP7 Switch Out 1
TP8 Switch 1 Fault
TP9 IC VIN Pin
TP10 PPTC Load Side
TP11 Invoke Overcurrent
ISL6118
