AS3676 datasheet(18/92 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



Battery voltage = 3.7V, LED dropout voltage = 3.5V. The 1:1 mode will be selected and there is 200mV drop on the

current sink and on the Charge Pump switch. Efficiency 95%.



Battery voltage = 3.5V, LED dropout voltage = 3.5V. The 1:1.5 mode will be selected and there is 1.5V drop on the

current sink and 250mV on the Charge Pump. Efficiency 66%.

The efficiency is dependent on the LED forward voltage given by:

Eff=(V_LED*Iout)/(Uin*Iin)

(EQ 4)

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



Automatic up all modes allowed (1:1, 1:1.5, 1:2)

- Start with 1:1 mode

- Switch up automatically 1:1 to 1:1.5 to 1:2



Automatic up, but only 1:1 and 1:1.5 allowed

- Start with 1:1 mode

- Switch up automatically only from 1:1 to 1:1.5 mode; 1:2 mode is not used



Manual

- Set modes 1:1, 1:1.5, 1:2 by software

Figure 13. Charge Pump Pin Connections

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

Note: The connections of the external capacitors C2, C3, C4 and C5 should be kept as short as possible.

Table 13. Charge Pump External Components

Symbol

Parameter

Condition

Min

Typ

Max

Unit

External Decoupling

Capacitor

Ceramic low-ESR capacitor between pins

VBAT and VSS.

1.0

µF

C3, C4

External Flying

Capacitor (2x)

Ceramic low-ESR capacitor between pins

C1_P and C1_N, between pins C2_P and

C2_N and between VBAT and VSS

1.0

µF

External Storage

Capacitor

Ceramic low-ESR capacitor between pins

CPOUT and VSS, pins CPOUT and VSS. Use

nominal 2.2µF capacitors (size 0603)

2.2

µF

AS3676

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