Supply Voltage Range (Typical). . . . . . . . . . . . . . . . . . 2.5V to 5.5V
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
1.
JA
is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
Electrical Specifications
PARAMETER
POWER SWITCH
ISL6121 On Resistance at 2.7V
V
SUPPLY
= 5V, Unless Otherwise Specified.
SYMBOL
TEST CONDITIONS
VIN = 2.7V, IOUT = 0.8A, T
A
= T
J
= 25
o
C
T
A
= T
J
= 85
o
C
VIN = 3.3V, IOUT = 0.8A, T
A
= T
J
= 25
o
C
T
A
= T
J
= 85
o
C
VIN = 5V, IOUT = 0.8A, T
A
= T
J
= 25
o
C
T
A
= T
J
= 85
o
C
MIN
TYP
MAX
UNITS
r
DS(ON)_27
-
-
-
-
-
-
-
-
-
-
60
-
50
-
50
-
300
10
10
3
70
80
60
75
60
75
450
-
-
-
m
m
m
m
m
m
mV
V/ms
V/ms
V/s
ISL6121 On Resistance at 3.3V
r
DS(ON)_33
ISL6121 On Resistance at 5.0V
r
DS(ON)_50
Disabled Output Voltage
Output Voltage Rising Rate
Slow VOUT Turn-off Rate
Fast VOUT Turn-off Rate
CURRENT CONTROL
Current Limit, VIN = 5V
OC Regulation Settling Time
Severe OC Regulation Settling Time
Over Current Latch-off Time
I/O PARAMETERS
Fault Output Voltage
ENABLE High Threshold
ENABLE Low Threshold
ENABLE Low Threshold
ENABLE Input Current
BIAS PARAMETERS
Enabled VIN Current
Disabled VIN Current
Under Voltage Lockout Threshold
UV Hysteresis
Over Temperature Disable
V
OUT_DIS
t_vout_rt
t_svout_offt
t_fvout_offt
VIN = 5V, Switch Disabled, 50A Load
R
L
= 10, C
L
= 0.1F, 10%-90%
R
L
= 10, C
L
= 0.1F, 90%-10%
R
L
= 1, C
L
= 0.1F, 90%-10%
Ilim
tsett
Ilim
tsett
Ilim_sev
t
OC_loff
VOUT = 3.3V
R
L
= 1.6C
L
= 0.1F to Within 10% of CR
R
L
< 1C
L
= 0.1F to Within 10% of CR
T
J
= 25
o
C
1.5
-
-
-
2
1
100
12
2.5
-
-
-
A
ms
s
ms
Vfault
Ven_vih
Ven_vil
Ven_vil
Ien_i
Fault Output Current = 10mA
VIN = 5.5V
VIN = 2.7V
VIN = 4.5V
ENABLE = 0V to 5V, VIN = 5V, T
J
>25
o
C
Switch Closed, OUTPUT = OPEN, T
J
> 0
o
C
Switch Open, OUTPUT = OPEN
VIN Rising, Switch Enabled
-
2.0
-
-
-0.5
-
-
-
-
0
0.4
-
0.6
0.8
0.5
V
V
V
V
A
I
VDD
I
VDD
V
UVLH
UV
HYS
Temp_dis
-
-
1.7
50
-
120
-
2.25
100
150
200
5
2.5
-
-
A
A
V
mV
o
C
FN9004 Rev 2.00
November 12, 2004
Page 3 of 11
ISL6121
Introduction
The ISL6121 is a single channel Overcurrent (OC) fault
protection IC for the +2.5V to +5V environment. Each
ISL6121 incorporates in a single 8 lead SOIC package a
50m N channel MOSFET power switch for power control.
See Figure 3 for switch resistance curves. With an enabling
input and fault reporting output compatible with 3V and 5V
logic allowing for external control and monitoring. See Figure
2 for IC operational waveforms. This device features internal
current monitoring, consistent current limiting and an
integrated power switch with a current limiting timed delay to
latch-off feature for system protection.
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 manufacturers’ 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 switch and the package
temp) to isolate a faulty load, the ISL6121 uses an internal
12ms timer that starts upon OC detection. Once an OC
condition is detected the output is current limited for a
nominal 12ms to allow transient conditions to pass before
latch-off. The time to latch-off is independent of the device’s
thermal condition.
If, after the ISL6121 has latched off, and the fault has
asserted and the enable is not deasserted but the OC
condition still exists, the ISL6121 unlike other IC devices
does not send to the controller a continuous string of fault
pulses. The ISL6121’s single fault signal is sent at the time
of latch off.
Key Feature Description and Operation
UV Lock Out
The ISL6121 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 and eliminates bus voltage
drooping caused by inrush current charging heavy load
capacitances. The rising and falling output is a current
limited voltage ramp 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 4 for turn-on wave forms.
Slow And Fast Shutdown
The ISL6121 has two shutdown modes. When disabled with
a Load Current less than the CR level the ISL6121 shuts
down in a controlled manner using a 500nA constant current
source controlled ramp. When latched-off during CR or if the
timer has expired the ISL6121 quickly pulls down the output
thereby quickly removing the faulted load from the voltage
bus. See Figures 9 and 10 for waveforms of each mode.
Temperature Shutdown
Although the ISL6121 has a thermal shutdown feature,
because of the 12ms timed shutdown this will only be
invoked in extremely high ambient temperatures.
Fault Blanking On Start-Up
During initial turn-on the ISL6121 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 11 through 13 for waveform
examples.
Active Output Pulldown
Another unique ISL6121 feature is the active pull down on
the outputs to within 300mV of GND when the device is
disabled.
Current Regulation
The ISL6121 has integrated current sensing on the power
MOSFET that allows for rapid control of OC events. Once an
OC is detected the ISL6121 goes into its Current Regulation
(CR) control mode. The ISL6121 CR level is set to a nominal
2A. This current regulation is
20%
over the full operating
temperature and voltage bias range. See Figures 5 and 6 for
illustrative curves.
The speed of this control is proportional to the magnitude of
the OC fault. Thus a hard over current is more quickly
controlled than a marginal condition. See Figure 7 for
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