AS3676 datasheet(15/92 Pages) AMSCO

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AS3676

Datasheet - D e ta i l e d D e s c r i p t i o n

8.2.3

Voltage Feedback

Setting bit step_up_fb (see page 15) = 00 enables voltage feedback at pin DCDC_FB. Capacitors C7 and C8 have to

be soldered in this operating mode.

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

UStep up_out = (R2+R3)/R3 *1.25 + IDCDC_FB * R2

(EQ 2)

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

UStep up_out = 1.25 + IDCDC_FB * R2

(EQ 3)

Where:

UStep up_out = Step Up DC/DC Converter output voltage

R2 = Feedback resistor R2

R3 = Feedback resistor R3

IDCDC_FB = Tuning current at ball DCDC_FB; 0 to 31µA

Note: The voltage on CURR1, CURR2 and CURR6 must not exceed 26V (see page 25)

8.2.4

PCB Layout Hints

To ensure good EMC performance of the DCDC converter, keep its external power components C6, R1, L1, Q1, D1

and C9 close together. Connect the ground of C6, R1 and C9 locally together and connect this with a short path to

AS3676 VSS. This ensures that local high-frequency currents will not flow to the battery.

8.2.5 Unused DCDC converter

If the DCDC converter is not used, connect DCDC_SNS to GND. DCDC_FB

3 and DCDC_GATE can be left open.

Table 9. Voltage Feedback Example Values

IDCDC_FB

UStep up_out

µA

R2 = 1M

, R3 not used

R2 = 500k

, R3 = 50k

13.75

14.25

14.75

15.25

15.75

6.25

16.25

7.25

16.75

8.25

17.25

9.25

17.75

10.25

18.25

11.25

18.75

12.25

19.25

13.25

19.75

14.25

20.25

15.25

20.75

16.25

21.25

………

31.25

28.75

32.25

29.25

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