AS3689 datasheet(14/72 Pages) AMSOSRAM

14 / 72 page

AS3689

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (mlg, ptr)

Revision 1.0.2 / 20070115

12 - 70

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

11 –Step Up DC/DC Converter Block Diagram; Option: Regulated Output Current, Overvoltage protection at Pin DCDC_FB

CURR1

CURR2

HV Current Sinks

each 0.156-40mA

CURR6

DCDC_GATE

DCDC_FB

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

4.7µF

C10

1.5nF

1µF

Battery

10µH

C11

15nF

100k

D10

D12

D11

D13

D15

D14

D16

SENSE_N

SENSE_P

7.2.3 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 = (R3+R4)/R4 x 1.25 + IDCDC_FB x R3

If R4 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 R3

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