AS3722 datasheet(35/198 Pages) AMSCO

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[v1-01] 2015-Sep-07

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AS3722 − Detailed Descriptions- Power Management Functions

Only in the case the load current gets so small that less than the

minimum on-time of the PMOS would be needed to keep the

loop in regulation the regulator will enter low power mode

operation. The crossover point is about ~1% of the DCDC

current limit.

High Efficiency Operation (Default Setting)

Bit settings: sdX_low_noise=0

In this mode there is a minimum coil current necessary before

switching off the PMOS. As a result there are less pulses

necessary at low output loads, and therefore the efficiency at

low output load is increased. As drawback this mode increases

the ripple up to a higher output current.

The crossover point to low power mode is already reached at

reasonable high output currents (~10% of the DCDC current

limit).

It’s possible to switch between these two modes during

operation.

Low Power Operation (sdX_low_power=1)

In this mode the controller is only running on a single phase.

Only one output stage of the external power stage is used to

reduce the power consumption for e.g. a stand-by mode

operation.

Power Save Operation (Automatically Controlled)

As soon as the output voltage stays above the desired target

value for a certain time, some internal blocks will be powered

down leaving the output floating to lower the power

consumption. Normal operation starts as soon as the output

drops below the target value for a similar amount of time. To

minimize the accuracy error some internal circuits are kept

powered to assure a minimized output voltage ripple.

Two addition guard bands, based on comparators, are set at

±5% of the target value to react quickly on large

over/under-shoots by immediately turning on the output

drivers without the normal time delays. This ensures a

minimized ripple also in very extreme load conditions.

Force PWM Mode Operation

Even in the case the load current gets so small that less than

the minimum on-time of the PMOS would be needed to keep

the loop in regulation the regulator will still stay on the fixed

switching frequency without entering low power mode. To

guarantee a stable output voltage also negative coil currents

are possible. This mode guarantees the lowest possible ripple

and a fixed frequency over all load conditions for powering

noise sensitive RF circuits, but is compromising on the

efficiency. The mode is enabled by setting sdX_force_pwm =1.

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