TPS7201Q, TPS7225Q, TPS7228Q, TPS7230Q

TPS7233Q, TPS7248Q, TPS7250Q, TPS72xxY

MICROPOWER LOW-DROPOUT (LDO) VOLTAGE REGULATORS

SLVS102F – MARCH 1995 – REVISED NOVEMBER 1998

28

POST OFFICE BOX 655303

APPLICATION INFORMATION

The design of the TPS72xx family of low-dropout (LDO) regulators is based on the higher-current TPS71xx

family. These new families of regulators have been optimized for use in battery-operated equipment and feature

extremely low dropout voltages, low supply currents that remain constant over the full-output-current range of

the device, and an enable input to reduce supply currents to less than 0.5

µA when the regulator is turned off.

device operation

The TPS72xx uses a PMOS pass element to dramatically reduce both dropout voltage and supply current over

more conventional PNP-pass-element LDO designs. The PMOS transistor is a voltage-controlled device that,

unlike a PNP transistor, does not require increased drive current as output current increases. Supply current

in the TPS72xx is essentially constant from no-load to maximum.

Current limiting and thermal protection prevent damage by excessive output current and/or power dissipation.

The device switches into a constant-current mode at approximately 1 A; further load increases reduce the output

voltage instead of increasing the output current. The thermal protection shuts the regulator off if the junction

temperature rises above 165

°C. Recovery is automatic when the junction temperature drops approximately 5°C

below the high temperature trip point. The PMOS pass element includes a back diode that safely conducts

reverse current when the input voltage level drops below the output voltage level.

A logic high on the enable input, EN, shuts off the output and reduces the supply current to less than 0.5

µA.

EN should be grounded in applications where the shutdown feature is not used.

Power good (PG) is an open-drain output signal used to indicate output-voltage status. A comparator circuit

continuously monitors the output voltage. When the output drops to approximately 95% of its nominal regulated

value, the comparator turns on and pulls PG low.

Transient loads or line pulses can also cause activation of PG if proper care is not taken in selecting the input

and output capacitors. Load transients that are faster than 5

µs can cause a signal on PG if high-ESR output

capacitors (greater than approximately 7

Ω) are used. A 1-µs transient causes a PG signal when using an output

capacitor with greater than 3.5

Ω of ESR. It is interesting to note that the output-voltage spike during the transient

can drop well below the reset threshold and still not trip if the transient duration is short. A 1-

µs transient must

drop at least 500 mV below the threshold before tripping the PG circuit. A 2-

µs transient trips PG at just 400 mV

below the threshold. Lower-ESR output capacitors help by reducing the drop in output voltage during a transient

and should be used when fast transients are expected.

A typical application circuit is shown in Figure 31.