LM3544

SNVS062C – AUGUST 2000 – REVISED MAY 2013

www.ti.com

When a port is in a current-limit condition, the LM3544 senses the output voltage on that port and, if it is less

than 1.0V (typ.), will reduce the output current through that port. This operation is shown in Figure 22, below. The

current reduction, or foldback, reduces power dissipation through the overloaded MOSFET switch. An additional

advantage of the foldback feature is the reduction of power required from the source supply when one or more

output ports are shorted.

Figure 22. Short-Circuit Output Current (with Foldback) vs. Output Voltage

THERMAL SHUTDOWN

The LM3544 is internally protected against excessive power dissipation by a two-stage thermal protection circuit.

If the device temperature rises to approximately 145°C, the thermal shutdown circuitry turns off any switch that is

current limited. Non-overloaded switches continue to function normally. If the die temperature rises above 160°C,

all switches are turned off and all four fault flag outputs are activated. Hysteresis ensures that a switch turned off

by thermal shutdown will not be turned on again until the die temperature is reduced to 135°C. Shorted switches

will continue to cycle off and on, due to the rising and falling die temperature, until the short is removed.\

The thermal shutdown function is shown graphically in Figure 23 and Figure 24.

Figure 23. Thermal Shutdown Characteristics

when only the First-Stage Thermal-Shutdown Mode is Needed

10

Submit Documentation Feedback

Copyright © 2000–2013, Texas Instruments Incorporated

Product Folder Links: LM3544