AS3687 datasheet(9/55 Pages) AMSCO

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AS3687/87XM

Datasheet

www.austriamicrosystems.com/AS3687

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Detailed Functional Description

7.1

Step Up DC/DC Converter

The Step Up DC/DC Converter is a high-efficiency current mode PWM regulator, providing output voltage up to e.g.

25V/35mA or e.g. 16V/55mA. A constant switching-frequency results in a low noise on the supply and output voltages.

Figure

11 – Step Up DCDC Converter Block Diagramm Option: Current Feedback with Overvoltage protection

CURR1

CURR2

HV Current Sinks

each 0.156-40mA

CURR6

Step Up DC/DC

Converter

4.7µF

1.5nF

DCDC_SNS

DCDC_GATE

DCDC_FB

100k

15nF

1µF

Battery

10µH

D10

D11

D13

D12

D14

Table

3 – Step Up DC/DC Converter Parameters

Symbol

Parameter

Min

TYP

Max

Unit

Note

IVDD

Quiescent Current

140

µ A

Pulse skipping mode.

VFB1

Feedback Voltage for

External Resistor Divider

1.20

1.25

1.30

For constant voltage control.

step_up_res

= 1

VFB2

Feedback Voltage for Current

Sink Regulation

0.4

0.5

0.6

on CURR1, CURR2 or CURR6 in

regulation.

step_up_res

= 0

Additional Tuning Current at

Pin DCDC_FB and

overvoltage protection

µ A

IDCDC_FB

Accuracy of Feedback

Current at full scale

-6

Adjustable by software using

μA step size (0-15µA)

VPROTECT = 1.25V +

IDCDC_FB * R2

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