AS3687 datasheet(11/55 Pages) AMSCO

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AS3687/87XM

Datasheet

www.austriamicrosystems.com/AS3687

1v3-4

10 - 54

Notes:

The voltage on the pin DCDC_FB is limited by an internal protection diode to VBAT + one diode

forward voltage (typ. 0.6V).

If the overvoltage protection is not used in current feedback mode, connect DCDC_FB to ground.

Figure

12 –Step Up DC/DC Converter Detail Diagram; Option: Regulated Output Current, Feedback is automatically selected between CURR1,

CURR2, CURR6 (step_up_fb_auto=1); overvoltage protection is enabled (step_up_prot=1); 1MHz clock frequency (step_up_freq=0)

CURR1

CURR2

HV Current Sinks

each 0.156-40mA

CURR6

4.7µF

1.5nF

DCDC_SNS

DCDC_GATE

DCDC_FB

100k

15nF

1µF

Battery

10µH

D10

D11

D13

D12

D14

1.25V

0.5V

step_up_vtuning

1.25V

step_up_prot

step_up_fb

ramp

PWM

Logic

Gate

Driver

Vrsense_max

step_up_freq

1MHz

500kHz

clk

ov_curr

Automatic

feedback select

(CURR1,2,6)

step_up_fb_auto

CURRX on and

currX_on_cp=0

1.35V

0.8V

overshoot comp

error ota

7.1.3 Voltage Feedback

Setting bit step_up_fb = 00 enables voltage feedback at pin DCDC_FB..

The output voltage is regulated to a constant value, given by (Bit step_up_res should be set to 1 in this

configuration)

Ustepup_out = (R2+R3)/R3 x 1.25 + IDCDC_FB x R2

If R3 is not used, the output voltage is by (Bit step_up_res should be set to 0 in this configuration):

Ustepup_out = 1.25 + IDCDC_FB x R2

Where:

Ustepup_out = Step Up DC/DC Converter output voltage.

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