Datasheet

I
LIMIT
Load
Current
GATE
Pin
TIMER
Pin
1.72V
1V
1 2 3 7 8
2 mA
pulldown
20 PA
Gate Charge
80 PA
t
RESTART
Fault Timeout
Period
0.3V
Fault
Detection
2.5 PA
LM25061
SNVS611E –FEBRUARY 2011–REVISED MARCH 2013 www.ti.com
The LM25061-2 provides an automatic restart sequence which consists of the TIMER pin cycling between 1.72V
and 1V seven times after the Fault Timeout Period, as shown in Figure 25. The period of each cycle is
determined by the 80 µA charging current, and the 2.5 µA discharge current, and the value of the capacitor C
T
.
When the TIMER pin reaches 0.3V during the eighth high-to-low ramp, the 20 µA current source at the GATE pin
turns on Q1. If the fault condition is still present, the Fault Timeout Period and the restart cycle repeat.
The Fault Timeout Period during restart cycles is approximately 18% shorter than the initial fault timeout period
which initiated the restart cycle. This is due to the fact that the TIMER pin transitions from 0.3V to 1.72V after
each restart time, rather than from ground.
Figure 25. Restart Sequence (LM25061-2)
Under-Voltage Lock-Out (UVLO)
The series pass MOSFET (Q1) is enabled when the input supply voltage (V
SYS
) is greater than the
programmable under-voltage lockout (UVLO) level. Typically the UVLO level at V
SYS
is set with a resistor divider
(R1-R2) as shown in Figure 21. Refering to the Block Diagram when V
SYS
is below the UVLO level, the internal
20 µA current source at UVLO is enabled, and Q1 is held off by the 2 mA pull-down current at the GATE pin. As
V
SYS
is increased, raising the voltage at UVLO above its threshold the 20 µA current source at UVLO is switched
off, increasing the voltage at UVLO, providing hysteresis for this threshold. With the UVLO pin above its
threshold, Q1 is switched on by the 20 µA current source at the GATE pin if the insertion time delay has expired.
See the Applications Section for a procedure to calculate the values of the threshold setting resistors (R1-R2).
The minimum possible UVLO level at V
SYS
can be set by connecting the UVLO pin to VIN. In this case Q1 is
enabled after the insertion time.
Shutdown Control
The load current can be remotely switched off by taking the UVLO pin below its threshold with an open collector
or open drain device, as shown in Figure 26. Upon releasing the UVLO pin the LM25061 switches on the load
current with in-rush current and power limiting.
Figure 26. Shutdown Control
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