95%

5%

EN

TPS65708

SLVSAE1A

– OCTOBER 2010 – REVISED FEBRUARY 2011

www.ti.com

SOFT START

The step-down converter in TPS65708 has an internal soft start circuit that controls the ramp up of the output

voltage. The output voltage ramps up from 5% to 95% of its nominal value within typical 250

µs. This limits the

inrush current in the converter during ramp up and prevents possible input voltage drops when a battery or high

impedance power source is used.

Figure 13. Soft Start

100% DUTY CYCLE LOW DROPOUT OPERATION

The device starts to enter 100% duty cycle mode once the input voltage comes close to the nominal output

voltage. In order to maintain the output voltage, the High Side MOSFET switch is turned on 100% for one or

more cycles. With further decreasing VIN the High Side MOSFET switch is turned on completely. In this case,

the converter offers a low input-to-output voltage difference. This is particularly useful in battery-powered

applications to achieve longest operation time by taking full advantage of the whole battery voltage range. The

minimum input voltage to maintain regulation depends on the load current and output voltage, and can be

calculated as:

With

12

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