Datasheet

TPS65070, TPS65072, TPS65073

TPS650731, TPS650732, TPS650701, TPS650702, TPS650721

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SLVS950G –JULY 2009–REVISED MAY 2013

POWER SAVE MODE

The Power Save Mode is enabled by default. If the load current decreases, the converter will enter Power Save

Mode operation automatically. During Power Save Mode the converter skips switching and operates with

reduced frequency in PFM mode and with a minimum quiescent current to maintain high efficiency. The

converter will position the output voltage typically +1% above the nominal output voltage. This voltage positioning

feature minimizes voltage drops caused by a sudden load step.

The transition from PWM Mode to PFM Mode occurs once the inductor current in the Low Side MOSFET switch

becomes 0.

During the Power Save Mode the output voltage is monitored with a PFM comparator. As the output voltage falls

below the PFM comparator threshold of V

OUTnominal

+1%, the device starts a PFM pulse. For this the High Side

MOSFET switch will turn on and the inductor current ramps up. Then it will be turned off and the Low Side

MOSFET switch will be turned on until the inductor current becomes 0.

The converter effectively delivers a current to the output capacitor and the load. If the load is below the delivered

current the output voltage will rise. If the output voltage is equal or higher than the PFM comparator threshold,

the device stops switching and enters a sleep mode with typical 19μA current consumption.

In case the output voltage is still below the PFM comparator threshold, further PFM current pulses will be

generated until the PFM comparator threshold is reached. The converter starts switching again once the output

voltage drops below the PFM comparator threshold.

With a single threshold comparator, the output voltage ripple during PFM Mode operation can be kept very small.

The ripple voltage depends on the PFM comparator delay, the size of the output capacitor and the inductor

value. Increasing output capacitor values and/or inductor values will minimize the output ripple.

The PFM Mode is left and PWM Mode entered in case the output current can not longer be supported in PFM

Mode or if the output voltage falls below a second threshold, called PFM comparator low threshold. This PFM

comparator low threshold is set to –1% below nominal Vout, and enables a fast transition from Power Save

Mode to PWM Mode during a load step. In Power Save Mode the quiescent current is reduced typically to 19μA.

The Power Save Mode can be disabled through the I2C interface for each of the step-down converters

independent from each other. If Power Save Mode is disabled, the converter will then operate in fixed PWM

mode.

Dynamic Voltage Positioning

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

active in Power Save Mode. It provides more headroom for both the voltage drop at a load step, and the voltage

increase at a load throw-off. This improves load transient behavior. At light loads, in which the converter operates

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 drops until it reaches the PFM 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 Low Side MOSFET

switch.

Figure 30. Power Save Mode

Product Folder Links: TPS65070 TPS65072 TPS65073 TPS650731 TPS650732 TPS650701 TPS650702

TPS650721