Datasheet

OUT
IN
GND
FAULT
ILIM
EN
R
ILIM
20 kΩ
R
FAULT
100 k
Input
TPS2557
0.1 uF
Power Pad
C
LOAD
R
LOAD
C
RETRY
0.22 µF
Output
1 kΩ
Ω
OUT
IN
GND
FAULT
ILIM
EN
R
ILIM
20 kΩ
R
FAULT
100 k
External Logic
Signal & Driver
TPS2557
0.1 uF
Power Pad
C
LOAD
R
LOAD
C
RETRY
0.22 µF
Output
Input
Ω
TPS2556
TPS2557
SLVS931A – NOVEMBER 2009– REVISED FEBRUARY 2012 www.ti.com
AUTO-RETRY FUNCTIONALITY
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, FAULTpulls low EN. The part is disabled when EN is pulled below the turn-off
theshold, and FAULT goes high impedance allowing C
RETRY
to begin charging. The part re-enables when the
voltage on EN reaches the turn-on threshold. 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 20. 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 21. Auto-Retry Functionality With External EN Signal
TWO-LEVEL CURRENT-LIMIT CIRCUIT
Some applications require different current-limit thresholds depending on external system conditions. Figure 22
shows an implementation for an externally-controlled, two-level current-limit circuit. The current-limit threshold is
set by the total resistance from ILIM to GND (see previously discussed "Programming the Current-Limit
Threshold" section). A logic-level input enables/disables MOSFET Q1 and changes the current-limit threshold by
modifying the total resistance from ILIM to GND. Additional MOSFET/resistor combinations can be used in
parallel to Q1/R2 to increase the number of additional current-limit levels.
NOTE
ILIM should never be driven directly with an external signal.
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