TXS4555

SBOS550A

– FEBRUARY 2011 – REVISED MARCH 2011

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TRANSIENT RESPONSE

As with any regulator, increasing the size of the output capacitor reduces over/undershoot magnitude but

increases duration of the transient response.

MINIMUM LOAD

The TXS4555 is stable and well-behaved with no output load. Traditional PMOS LDO regulators suffer from

lower loop gain at very light output loads. The TXS4555 employs an innovative low-current mode circuit to

increase loop gain under very light or no-load conditions, resulting in improved output voltage regulation

performance down to zero output current.

THERMAL INFORMATION

Thermal Protection

Thermal protection disables the output when the junction temperature rises to approximately +160

°C, 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 the dissipation of the regulator, protecting it from damage

because of overheating.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate

heat sink. For reliable operation, junction temperature should be limited to +125

°C maximum. To estimate the

margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal

protection is triggered; use worst-case loads and signal conditions. For good reliability, thermal protection should

trigger at least +35

°C above the maximum expected ambient condition of your particular application. This

configuration produces a worst-case junction temperature of +125

°C at the highest expected ambient

temperature and worst-case load.

The internal protection circuitry of the TXS4555 has been designed to protect against overload conditions. It was

not intended to replace proper heat sinking. Continuously running the TXS4555 into thermal shutdown will

degrade device reliability.

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Copyright

© 2011, Texas Instruments Incorporated