t

=

120·R

L

120+R

L

·C

OUT

14

TLV733P

SBVS235C – OCTOBER 2014 – REVISED JULY 2019

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7.3 Feature Description

7.3.1 Undervoltage Lockout (UVLO)

The TLV733 uses an undervoltage lockout (UVLO) circuit that disables the output until the input voltage is

greater than the rising UVLO voltage, UVLORISE. This circuit ensures that the device does not exhibit any

unpredictable behavior when the supply voltage is lower than the operational range of the internal circuitry.

During UVLO disable, the output is connected to ground with a 120-Ω pulldown resistor.

7.3.2 Shutdown and Output Enable

The enable pin (EN) is active high. Enable the device by forcing the EN pin to exceed VEN(HI). Turn off the device

by forcing the EN pin to drop below VEN(LO). If shutdown capability is not required, connect EN to IN. There is no

internal pulldown resistor connected to the EN pin.

The TLV733 has an internal pulldown MOSFET that connects a 120-Ω resistor to ground when the device is

disabled. The discharge time after disabling depends on the output capacitance (COUT) and the load resistance

(RL) in parallel with the 120-Ω pulldown resistor. The time constant is calculated in Equation 1:

(1)

7.3.3 Internal Foldback Current Limit

The TLV733 has an internal foldback current limit that protects the regulator during fault conditions. The current

allowed through the device is reduced as the output voltage falls. When the output is shorted, the LDO supplies a

typical current of 150 mA. 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 is

shorted, the PMOS pass transistor dissipates power [(VIN – VOUT) × IOS] 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. See the Thermal

Information table for more details.

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

minimum current limit at nominal VOUT current limit (ILIM) during startup. See Figure 18 to Figure 20 for typical

foldback current limit values. If the output is loaded by a constant-current load during startup, 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 TLV733 has fully risen to its nominal output voltage.

The TLV733 PMOS pass element has an intrinsic body diode that conducts current when the voltage at the OUT

pin exceeds the voltage at the IN pin. Do not force the output voltage to exceed the input voltage because

excessively high current may flow through the body diode.

7.3.4 Thermal Shutdown

Thermal shutdown protection disables the output when the junction temperature rises to approximately 160°C.

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

junction temperature cools to approximately 140°C, the output circuitry is again enabled. Depending on power

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

This cycling limits regulator dissipation, protecting it 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 125°C

maximum. 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 TLV733 internal protection circuitry protects against overload conditions but is not intended to be activated in

normal operation. Continuously running the TLV733 into thermal shutdown degrades device reliability.