AS3676 datasheet(17/92 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

8.3

Charge Pump

The Charge Pump uses two external flying capacitors C3, C4 to generate output voltages higher than the battery volt-

age. There are three different operating modes of the charge pump itself:



1:1 Bypass Mode

- Battery input and output are connected by a low-impedance switch

- battery current = output current.



1:1.5 Mode

- The output voltage is up to 1.5 times the battery voltage (without load), but is limited to VCPOUTmax all the time

- battery current = 1.5 times output current.



1:2 Mode

- The output voltage is up to 2 times the battery voltage (without load), but is limited to VCPOUTmax all the time

- battery current = 2 times output current

As the battery voltage decreases, the Charge Pump must be switched from 1:1 mode to 1:1.5 mode and eventually in

1:2 mode in order to provide enough supply for the current sinks. Depending on the actual current the mode with best

overall efficiency can be automatically or manually selected:

Examples:

Table 12. DCDC control2

Addr: 22h

DCDC control2

This register controls the Step Up DC/DC Converter and low-voltage current

sinks CURR3x.

Bit

Bit Name

Default Access

Description

step_up_res

0R/W

Gain selection for Step Up DC/DC Converter

Select 0 if Step Up DC/DC Converter is used

with current feedback (CURR1, CURR2,

CURR6) or if DCDC_FB is used with current

feedback only – R2, C7, C8 connected, R3 not

used

Select 1 if DCDC_FB is used with external

resistor divider using 2 resistors: R2 and R3

skip_fast

0R/W

Step Up DC/DC Converter output voltage at low loads,

when pulse skipping is active

Accurate output voltage, more ripple

Elevated output voltage, less ripple

step_up_prot

1R/W

Step Up DC/DC Converter protection

No over voltage protection

Over voltage protection on pin DCDC_FB

enabled voltage limitation =1.25V on DCDC_FB

step_up_lowcur

0R/W

Step Up DC/DC Converter coil current limit

Normal current limit

Current limit reduced by approx. 33%

step_up_fb_auto

0R/W

step_up_fb selects the feedback of the DCDC

converter

If step_up_fb is not DCDC_FB (00), then

feedback is automatically chosen within the

current sinks CURR1, CURR2 and CURR6.

Only those are used for this selection, which are

enabled (currX_mode must not be 00) and not

connected to the charge pump (currX_on_cp

must be 0).

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