Datasheet

TPS709
www.ti.com 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.
Power dissipation depends on input voltage and load conditions. Power dissipation (P
D
) is equal to the product of
the output current and the voltage drop across the output pass element, as shown in Equation 1:
P
D
= (V
IN
– V
OUT
) × I
OUT
(1)
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