AS3676 datasheet(14/92 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

8.2.2

Over voltage Protection in Current Feedback Mode

The over voltage protection in current feedback mode (step_up_fb = 01, 10 or 11 or step_up_fb_auto = 1) works as fol-

lows: Only resistor R2 and C7/C8

2 is soldered and R3 is omitted. An internal current source (sink) is used to generate

a voltage drop across the resistor R2. If then the voltage on DCDC_FB is above 1.25V and step_up_prot=1, the DCDC

is momentarily disabled to avoid too high voltages on the output of the DCDC converter. When the voltage on

DCDC_FB drops below 1.25V, the DCDC automatically resumes operation.

The protection voltage can be calculated according to the following formula:

VPROTECT = 1.25V + IDCDC_FB * R2

(EQ 1)

Note: The voltage on the pin DCDC_FB is limited by an internal protection diode to VBAT + one diode forward volt-

age (typ. 0.6V).

If the over voltage 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); over voltage protection

is enabled (step_up_prot=1); 1MHz clock frequency (step_up_frequ=0)

2. If the DCDC converter is only used in current feedback mode (CURR1, CURR2 or CURR6 - and not used

for a constant voltage source), the capacitors C7 and C8 can be removed.

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AS3676

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