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Softstart and Short-Circuit Protection

Undervoltage Lockout

Overtemperature Protection

TPS61200

TPS61201

TPS61202

SLVS577B – MARCH 2007 – REVISED FEBRUARY 2008

After being enabled, the device starts operating. At first it keeps the main output VOUT disconnected, and

charges the capacitor at VAUX. If the capacitor at VAUX is charged to about 2.5 V, the device switches to

normal operation. This means VOUT is turned on and the capacitor at VOUT is charged while the load

connected to the device is supplied. To ramp up the output voltage in a controlled way, the average current limit

is set to 400 mA and rise proportional to the increase of the output voltage. At an output voltage of about 1.2 V,

the current limit is at its nominal value. If the output voltage does not increase, the current limit will not increase.

There is no timer implemented. Thus the output voltage overshoot at startup, as well as the inrush current, is

kept at a minimum. The device ramps up the output voltage in a controlled manner even if a large capacitor is

connected at the output. When the output voltage does not increase above 1.2 V, the device assumes a

short-circuit at the output, and keeps the current limit low to protect itself and the application. When there is a

short at the output during operation, the current limit is decreased accordingly.

An undervoltage lockout function prevents the main output at VOUT from being supplied if the voltage at UVLO

drops below 0.25 V. When using a resistive divider at the voltage to be monitored, for example the supply

voltage, any threshold for the monitored voltage can be programmed. If in undervoltage lockout mode, the device

still maintains its supply voltage at VAUX, but it is not turned off until EN is programmed low. This undervoltage

lockout function is implemented in order to prevent the malfunctioning of the converter.

The device has a built-in temperature sensor which monitors the internal IC temperature. If the temperature

exceeds the programmed threshold (see electrical characteristics table), the device stops operating. As soon as

the IC temperature has decreased below the programmed threshold, it starts operating again. There is a built-in

hysteresis to avoid unstable operation at IC temperatures at the overtemperature threshold.

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