TPS709

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SBVS186E – MARCH 2012 – REVISED NOVEMBER 2013

UNDERVOLTAGE LOCK-OUT (UVLO)

The TPS709xx use an undervoltage lockout (UVLO) circuit to keep the output shut off until the internal circuitry

operates properly.

REVERSE CURRENT PROTECTION

The TPS709xx have integrated reverse current protection. Reverse current protection prevents current from

flowing from the OUT pin to the IN pin when output voltage is higher than input voltage. The reverse current

protection circuitry places the power path in high impedance when it detects that the output voltage is higher than

the input voltage. This setting reduces leakage current from the output to the input to 10 nA, typical. The reverse

current protection is always active regardless of the enable pin logic state or if the OUT pin voltage is greater

than 1.8 V. Reverse current can flow if the output voltage is less than 1.8 V and if input voltage is less than the

output voltage.

If voltage is applied to the input pin, then the maximum voltage that can be applied to the OUT pin is the lower of

three times the nominal output voltage or 6.5 V. For example, if the 1.2-V output voltage version is used, then the

maximum reverse bias voltage that can be applied to the OUT pin is 3.6 V. If the 5.0-V output voltage version is

used, then the maximum reverse bias voltage that can be applied to the OUT pin is 6.5 V.

THERMAL INFORMATION

Thermal protection disables the output when the junction temperature rises to approximately +165°C, allowing

the device to cool. When the junction temperature cools to approximately +145°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 as a

result of overheating.

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

heatsink. For reliable operation, junction temperature should be limited to +125°C, maximum. To estimate the

margin of safety in a complete design (including heatsink), 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 the particular application. This

configuration produces a worst-case junction temperature of +125°C at the highest expected ambient

temperature and worst-case load.

The TPS709xx internal protection circuitry is designed to protect against overload conditions. This circuitry is not

intended to replace proper heatsinking. Continuously running the TPS709xx into thermal shutdown degrades

device reliability.

POWER DISSIPATION

The ability to remove heat from the die is different for each package type, which presents different considerations

in the printed circuit board (PCB) layout. The PCB area around the device that is free of other components

moves the heat from the device to ambient air. Performance data for JEDEC low and high-K boards are given in

the Thermal Information table. Using heavier copper increases the effectiveness in removing heat from the

device. The addition of plated through-holes to heat-dissipating layers also improves the heatsink effectiveness.

the output current and the voltage drop across the output pass element, as shown in Equation 1:

(1)

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