AS3677 datasheet(14/68 Pages) AMSCO

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AS3677

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 the external flying capacitor C4 to generate output voltages higher than the battery voltage.

There are two 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.

1:2 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 1:2 mode in order to provide

enough supply for the current sinks. Depending on the actual current the mode with best overall efficiency can be auto-

matically or manually selected:

The charge pump mode switching can be done manually or automatically with the following possible software settings:

Automatic

- Start with 1:1 mode

- Switch up automatically to 1:2 mode

Manual

- Set modes 1:1 and 1:2 by software

The Charge Pump requires the external components listed in the following table:

Note:

The connections of the external capacitors C4 and C5 should be kept as short as possible.

step_up_lowcur

1R/W

Step Up DC/DC Converter coil current limit

Normal current limit

Current limit reduced by approx. 33%

step_up_ov

Step Up DC/DC overvoltage triggered

No overvoltage triggered

Overvoltage triggered; this bit is automatically

reset by step_up_on=0

step_up_fb_auto

1R/W

step_up_fb select the feedback of the DCDC

converter

The feedback is automatically chosen within the

current sinks CURR1, CURR2 and CURR6

(never DCDC_FB). 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).

Table 11. Charge Pump External Components

Symbol

Parameter

Condition

Min

Typ

Max

Unit

External Flying

Capacitor

Ceramic low-ESR capacitor between pins

C1_P and C1_N

470

External Storage

Capacitor

Ceramic low-ESR capacitor between pins

CPOUT and VSS, pins CPOUT and VSS_CP

1.0

µF

Table 10. 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

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