AS3517H-ECTP datasheet(36/94 Pages) AMSCO

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AS3517 V17

Data Sheet, Confidential

www.austriamicrosystems.com

9.2.2

DCDC Step-Down Converter (3x)

General

These converters are meant to convert the battery voltage down to voltages which fit to the core and peripheral supply voltage

requirements for microprocessors.

•

Input Voltage BVDDC1, BVDDC2 & BVDDC3 (usually connected to the battery)

•

Output Voltage CVDD1, CVDD2 & CVDD3

•

output voltage levels can be programmed independently form 0.65V to 3.4V

•

the default value at start-up is defined by VPROG1 and VPROG2 pins

•

driver strength 250mA (500mA for DCDC 3)

Figure 20 DCDC Step-Down 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 97% 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 250mA, with an output capacitor of only 10

μF. The implemented current limitation protects the DCDC and the coil

during overload condition.

To achieve optimised performance in different applications, adjustable settings allow to compromise between high efficiency and low

input, output ripple:

Low ripple, low noise operation:

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. Especially in the

case of an inverted coil current the regulator will not operate in pulse skip mode.

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AS3517H-ECTP Datasheet(PDF) 36 Page - ams AG