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LP38690, LP38692

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SNVS322M – DECEMBER 2004 – REVISED DECEMBER 2015

Product Folder Links: LP38690 LP38692

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Copyright © 2004–2015, Texas Instruments Incorporated

7.3 Feature Description

7.3.1 Enable (EN)

The LP38692 has an Enable pin (EN) which allows an external control signal to turn the regulator output On and

Off. The Enable On/Off threshold has no hysteresis. The voltage signal must rise and fall cleanly, and promptly,

through the ON and OFF voltage thresholds. The EN pin voltage must be higher than the VEN(MIN) threshold to

ensure that the device is fully enabled under all operating conditions. The EN pin voltage must be lower than the

VEN(MAX) threshold to ensure that the device is fully disabled. The Enable pin has no internal pull-up or pull-down

to establish a default condition and, as a result, this pin must be terminated either actively or passively. If the

Enable pin is driven from a source that actively pulls high and low, the drive voltage should not be allowed to go

below ground potential or higher than VIN. If the application does not require the Enable function, the pin should

be connected directly to the IN pin.

7.3.2 Thermal Shutdown Protection (TSD)

Thermal shutdown disables the output when the junction temperature rises to approximately 160°C which allows

the device to cool. When the junction temperature cools to approximately 150°C, the output circuitry enables.

Based on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may

cycle on and off. This thermal cycling limits the dissipation of the regulator and protects it from damage as a

result of overheating.

The TSD circuitry of the LP38692 has been designed to protect against temporary thermal overload conditions.

The TSD circuitry was not intended to replace proper heat-sinking. Continuously running the LP38692 device into

thermal shutdown degrades device reliability.

7.3.3 Foldback Current Limiting

Foldback current limiting is built into the LP38690 and LP38692 which reduces the amount of output current the

part can deliver as the output voltage is reduced. The amount of load current is dependent on the differential

voltage between VIN and VOUT. Typically, when this differential voltage exceeds 5 V, the load current limits at

about 450 mA. When the VIN – VOUT differential is reduced below 4 V, load current is limited to about 1500 mA.

CAUTION

When toggling the LP38692 Enable (EN) after the input voltage (VIN) is applied, the

foldback current limit circuitry is functional the first time that the EN pin is taken high.

The foldback current limit circuitry is non-functional the second, and subsequent, times

that the EN pin is taken high. Depending on the input and output capacitance values

the input inrush current may be higher than expected which can cause the input

voltage to droop.

If the EN pin is connected to the IN pin, the foldback current limit circuitry is functional

when VIN is applied if VIN starts from less than 0.4 V.

7.4 Device Functional Modes

7.4.1 Enable (EN)

The EN pin voltage must be higher than the VEN(MIN) threshold to ensure that the device is fully enabled under all

operating conditions.

7.4.2 Minimum Operating Input Voltage (VIN)

The LP38690 and LP38692 devices do not include any dedicated UVLO circuitry. The LP38690 and LP38692

internal circuitry is not fully functional until VIN is at least 2.7 V. The output voltage is not regulated until VIN ≥

(VOUT + VDO), or 2.7 V, whichever is higher.