TLV755P datasheet(13/44 Pages) TI

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TLV755P

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SBVS320A – NOVEMBER 2017 – REVISED MAY 2018

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Feature Description (continued)

The EN pin is independent of the input pin (IN), but if the EN pin is driven to a higher voltage than VIN, the

current into the EN pin increases. This effect is illustrated in Figure 23. When the EN voltage is higher than the

input voltage there is an increased current flow into the EN pin. If this increased flow causes problems in the

application, sequence the EN pin after VIN is high, or to tie EN to VIN to prevent this flow increase from

happening. If EN is driven to a higher voltage than VIN, limit the frequency on EN to below 10 kHz.

7.3.3 Internal Foldback Current Limit

The TLV755P has an internal current limit that protects the regulator during fault conditions. The current limit is a

hybrid scheme with brick wall until the output voltage is less than 0.4 V × VOUT(NOM). When the voltage drops

below 0.4 V × VOUT(NOM), a foldback current limit is implemented that scales back the current as the output

voltage approaches GND. When the output shorts, the LDO supplies a typical current of ISC. The output voltage

is not regulated when the device is in current limit. In this condition, the output voltage is the product of the

regulated current and the load resistance. When the device output shorts, the PMOS pass transistor dissipates

power [(VIN – VOUT) × ISC] until thermal shutdown is triggered and the device turns off. After the device cools

down, the internal thermal shutdown circuit turns the device back on. If the fault condition continues, the device

cycles between current limit and thermal shutdown.

The foldback current-limit circuit limits the current that is allowed through the device to current levels lower than

the minimum current limit at nominal VOUT current limit (ICL) during start up. See Figure 26 for typical current limit

values. If the output is loaded by a constant-current load during start up, or if the output voltage is negative when

the device is enabled, then the load current demanded by the load may exceed the foldback current limit and the

device may not rise to the full output voltage. For constant-current loads, disable the output load until the output

has risen to the nominal voltage.

Excess inductance can cause the current limit to oscillate. Minimize the inductance to keep the current limit from

oscillating during a fault condition.

7.3.4 Thermal Shutdown

Thermal shutdown protection disables the output when the junction temperature rises to approximately 165°C.

Disabling the device eliminates the power dissipated by the device, allowing the device to cool. When the

junction temperature cools to approximately 155°C, the output circuitry is enabled again. Depending on power

dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may cycle on and off.

This cycling limits regulator dissipation that protects the circuit from damage as a result of overheating.

Activating the thermal shutdown feature usually indicates excessive power dissipation as a result of the product

of the (VIN – VOUT) voltage and the load current. For reliable operation, limit junction temperature to a maximum

of 125°C. To estimate the margin of safety in a complete design, increase the ambient temperature until the

thermal protection is triggered; use worst-case loads and signal conditions.

The internal protection circuitry protects against overload conditions but is not intended to be activated in normal

operation. Continuously running the device into thermal shutdown degrades device reliability.

TLV755P Datasheet(PDF) 13 Page - Texas Instruments