AS3715 datasheet(21/160 Pages) AMSCO

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ams Datasheet, Confidential

Page 21

[v1-00] 2014-Sep-10

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AS3715 − Detailed Description – Power Management Functions

Mode Settings

Low Ripple, Low Noise Operation:

Bit settings: sdX_low_noise=1

In this mode there is no minimum coil current necessary before

switching OFF the PMOS. As long as the load current is superior

to the ripple current the device operates in continuous mode.

When the load current gets lower, the discontinuous mode is

triggered. As result, the auto-zero comparator stops the NMOS

conduction to avoid load discharger and the duty cycle is

reduced down to tmin_on to keep the regulation loop stable.

This results in a very low ripple and noise, but decreased

efficiency, at light loads, especially at low input to output

voltage differences.

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

(phase 1). 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.

AS3715 Datasheet(PDF) 21 Page - ams AG

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