Datasheet

3
885 7 10= ´ ´
SD CT
T . C
3
40 x 10
=
FAULT
CT
T
C
EN
VIN
GND ISET
VOUT
PG
CT
TPS2421-x
1
2
3
FLT
4 5
6
7
8
TPS2421-1
TPS2421-2
SLUS907G –JANUARY 2009–REVISED MAY 2013 www.ti.com
PINOUT DIAGRAM
Table 1. TERMINAL FUNCTIONS
FUNCTION PIN NO. DESCRIPTION
FLT 1 Fault low indicated the fault time has expired and the FET is switched off
EN 2 Device is enabled when this pin is pulled low
VIN 3 Power In and control supply voltage
GND 4 GND
ISET 5 A resistor to ground sets the fault current, the current limit is 125% of the fault current. TPS2421 only
CT 6 A capacitor to ground sets the fault time
VOUT 7 Output to the load
PG 8 Power Good low represents the output voltage is within 300 mV of the input voltage
PIN DESCRIPTION
CT: Connect a capacitor from CT to GND to set the fault time. The fault timer starts when I
VOUT
exceeds I
SET
or
when SOA protection mode is active, charging the capacitor with 35 μA from GND towards an upper threshold of
1.4 V. If the capacitor reaches the upper threshold, the internal pass MOSFET is turned off. For TPS2421-1, the
MOSFET will remain off until EN is cycled. For TPS2421-2, the capacitor will discharge at 1.4 μA to 0.16 V and
then re-enable the pass MOSFET. If the upper threshold is not crossed, the capacitor will discharge at 40 μA to
0.16 V and then to 0 V at 1.4 μA. When the device is disabled, CT is pulled to GND through a 50-kΩ resistor.
The timer period must be chosen long enough to allow the external load capacitance to charge. The nominal (not
including component tolerances) fault timer period is selected using Equation 1 where T
FAULT
is the minimum
timer period in seconds and C
CT
is in Farads.
(1)
For TPS2421-2, the second and subsequent retry timer periods will be slightly shorter than the first retry period.
CT nominal (not including component tolerances) discharge time, t
SD
from 1.4 V to 0.16 V is shown in
Equation 2, where C
CT
is in Farads and t
SD
is in seconds.
(2)
The nominal ratio of on to off times represents about a 3.7% duty cycle when a hard fault is present on the
output.
FLT: Open-drain output that pulls low on any condition that causes the output to open. These conditions are
either an overload with a fault time-out, or a thermal shutdown. FLT becomes operational before UV, when V
VIN
is greater than 1 V. FLT will pulse low momentarily prior to the onset of V
VOUT
ramp up during IN or EN based
start up.
GND: This is the most negative voltage in the circuit and is used as reference for all voltage measurements
unless otherwise specified.
ISET: A resistor from this pin to GND sets both the fault current (I
SET
) and current limit (I
LIM
) levels. The current
limit is internally set at 150% of the fault current. The fault timer described in the CT section starts when I
VOUT
exceeds I
SET
.
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