AS3658F-BCTP datasheet(71/158 Pages) AMSCO

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AS3658

Data Sheet Confidential - Detail ed Descri ption-Power Management Functions

8.11.2 Step Down DC/DC Converter Characteristics

Figure 27. Step Down DC/DC Converter Block diagram

Functional Description

The step-down converter is a high efficiency fixed frequency current mode regulator. By using low resistance internal

PMOS and NMOS switches efficiency up to 95% can be achieved. The fast switching frequency allows using small

inductors, without increasing the current ripple. The unique feedback and regulation circuit guarantees optimum load

and line regulation over the whole output voltage range, up to an output current of 500mA, with an output capacitor of

only 10µF. The implemented current limitation protects the DCDC and the coil during overload condition.

To allow optimized performance in different applications, there are bit settings possible, to get the best compromise

between high efficiency and low input, output ripple:

Low ripple, low noise operation:

Bit settings:

sdX_dis_curmin=1

In this mode there is no minimum coil current necessary before switching off the PMOS. As result, the ON time of the

PMOS will be reduced down to tmin_on at no or light load conditions, even if the coil current is very small or the coil

current is inverted. This results in a very low ripple and noise, but decreased efficiency, at light loads, especially at low

input to output voltage differences. Because of the inverted coil current in that case the regulator will not operate in

pulse skip mode.

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AS3658F-BCTP Datasheet(PDF) 71 Page - ams AG