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Dynamic Voltage Positioning

+1%

-1%

PWMMode

medium/heavyload

PFMMode

lightload

Smooth

increasedload

PWMMode

medium/heavyload

PFMMode

lightload

Fastloadtransient

COMP_LOWthreshold

Soft Start

V

OUT

EN

95%

5%

t

Start

t

RAMP

TPS65053

SLVS754 – MARCH 2007

DETAILED DESCRIPTION (continued)

This feature reduces the voltage under/overshoots at load steps from light to heavy load and vice versa. It is

activated in Power Save Mode operation when the converter runs in PFM Mode. It provides more headroom for

both the voltage drop at a load step increase and the voltage increase at a load throw-off. This improves load

transient behavior.

At light loads, in which the converters operate in PFM Mode, the output voltage is regulated typically 1% higher

than the nominal value. In case of a load transient from light load to heavy load, the output voltage will drop until

it reaches the skip comparator low threshold set to –1% below the nominal value and enters PWM mode. During

a load throw off from heavy load to light load, the voltage overshoot is also minimized due to active regulation

turning on the N-channel switch.

Figure 19. Dynamic Voltage Positioning

The two converters have an internal soft start circuit that limits the inrush current during start-up. During soft

start, the output voltage ramp up is controlled as shown in Figure 20.

Figure 20. Soft Start

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