Datasheet

AUTO-RETRY FUNCTIONALITY
OUT
IN
GND
FAULT
ILIM
EN
Input
TPS2551
PowerPad
Output
0.1 Fm
R
100k
FAULT
W
C
0.1 F
RETRY
m
R
20k
ILIM
W
C
LOAD
R
LOAD
1kW
OUT
IN
GND
FAULT
ILIM
EN
ExternalLogic
Signal&Driver
TPS2551
PowerPad
Input
0.1 Fm
R
100k
FAULT
W
C
0.1 F
RETRY
m
R
20k
ILIM
W
C
LOAD
R
LOAD
1kW
Output
LATCH-OFF FUNCTIONALITY
TPS2550
TPS2551
www.ti.com ........................................................................................................................................ SLVS736B – FEBRUARY 2008 – REVISED NOVEMBER 2008
Some applications require that an overcurrent condition disables the part momentarily during a fault condition
and re-enables after a pre-set time. This auto-retry functionality can be implemented with an external resistor and
capacitor. During a fault condition, FAULT pulls low disabling the part. The part is disabled when EN is pulled
low, and FAULT goes high impedance allowing C
RETRY
to begin charging. The part re-enables when the voltage
on EN reaches the turnon threshold, and the auto-retry time is determined by the resistor/capacitor time
constant. The part will continue to cycle in this manner until the fault condition is removed.
Figure 22. Auto-Retry Functionality
Some applications require auto-retry functionality and the ability to enable/disable with an external logic signal.
The figure below shows how an external logic signal can drive EN through R
FAULT
and maintain auto-retry
functionality. The resistor/capacitor time constant determines the auto-retry time-out period.
Figure 23. Auto-Retry Functionality With External EN Signal
The circuit in Figure 24 uses an SN74HC00 quad-NAND gate to implement overcurrent latch-off. The SN74HC00
high-speed CMOS logic gate is selected because it operates over the 2.5V – 6.5V range of the TPS2550/51.
This circuit is designed to work with the active-high TPS2551. ENABLE must be logic low during start-up until V
IN
is stable to ensure that the switch initializes in the OFF state. A logic high on ENABLE turns on the switch after
V
IN
is stable. FAULT momentarily pulls low during an overcurrent condition, which latches STAT logic low and
disables the switch. The host can monitor STAT for an overcurrent condition. Toggling ENABLE resets STAT and
re-enables the switch.
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