Input

Voltage

STOP

RUN

LM25085

RT

VIN

6

- 8.6

LM25085, LM25085-Q1

www.ti.com

SNVS593H – OCTOBER 2008 – REVISED MARCH 2013

following:

where

•

(5)

SHUTDOWN

The LM25085 can be shutdown by grounding the RT pin (see Figure 25). In this mode the PFET is held off, and

the VCC regulator is disabled. The internal operating current is reduced to the value shown in Figure 6. The

shutdown threshold at the RT pin is

≊0.73V, with ≊50mV of hysteresis. Releasing the pin enables normal

operation. The RT pin must not be forced high during normal operation.

Figure 25. Shutdown Implementation

CURRENT LIMITING

MOSFET has a wide process variation and a large temperature coefficient.

comparator switches to turn off Q1. Current sensing is disabled for a blanking time of

≊100ns at the beginning of

the on-time to prevent false triggering of the current limit comparator due to leading edge current spikes.

Because of the blanking time and the turn-on and turn-off delays created by the PFET, the on-time at the PGATE

pin should not be set less than 150ns. An on-time shorter than that may prevent the current limit detection circuit

from properly detecting an over-current condition. The duration of the subsequent forced off-time is a function of

the input voltage and the voltage at the FB pin, as shown in Figure 10. The longer-than-normal forced off-time

allows the inductor current to decrease to a low level before the next on-time. This cycle-by-cycle monitoring,

followed by a forced off-time, provides effective protection from output load faults over a wide range of operating

conditions.

(6)

Copyright © 2008–2013, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM25085 LM25085-Q1