AS3668 datasheet(14/59 Pages) AMSCO

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AS3668

Data Sheet - Detailed Description

8 Detailed Description

8.1 Charge Pump

The Charge Pump uses the external flying capacitor CFLY 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

Figure 22. Charge Pump Block Diagram .

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 automatically 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 CVCPOUT and CFLY should be kept as short as possible.

Table 5. Charge Pump External Components

Symbol

Parameter

Condition

Min

Typ

Max

Unit

CFLY

External Flying Capacitor

Ceramic low-ESR capacitor between pins CP and CN

470

CVCPOUT

External Storage Capacitor Ceramic low-ESR capacitor between pins VCP and VSS

1.0

μF

Table 6. Charge Pump Characteristics

Symbol

Parameter

Condition

Min

Typ

Max

Unit

ICPOUT

Output Current

Continuous

Depending on PCB layout

0.0

VCPOUTmax

Output Voltage

Internally limited, Including output ripple

5.6



Efficiency

Including current sink loss;

ICPOUT = 60mA.

ICP1_2

Power Consumption

without Load,

fclk = 1 MHz

1:2 Mode

2.5

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