AS3668 datasheet(15/60 Pages) AMSCO

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AS3668

Data Sheet - D e t a i l e d D e s c r i p t i o n

8.1.1

Charge Pump Mode Switching

If automatic mode switching is enabled the charge pump monitors the current sources, which are directly connected to the output of the charge

pump VCP. In order to identify the enabled current sources, the related registers should be setup before starting the charge pump. If any of the

voltage on these current sources drops below the threshold (Vcurr_source), the higher mode is selected after the debounce time (tdeb).

The charge pump mode switching supports only a mode change to a higher charge pump mode (e.g.: mode 1:1 to mode 1:2). In case VBAT

increases again during operation the automatic mode switching will not change the operation mode from 1:2 down to 1:1. In order to change the

mode all current sources must be switched off to reset the charge pump mode switching mechanism. After enabling the current sources again

the mode switching mechanism chooses the appropriate mode for the optimized operation of the charge pump either in 1:1 mode or 1:2 mode. In

case an automatic pattern is used the current sources get a reset after each pattern cycle because the current sources are automatically

switched off when executing a pattern after each cycle.

Figure 23. Charge Pump Mode Switching .

8.1.2

Soft Start

An implemented soft start mechanism reduces the inrush current. Battery current is smoothed when switching the charge pump on and also at

each switching condition. This precaution reduces electromagnetic radiation significantly.

8.1.3

Unused Charge Pump

If the charge pump is not used, capacitors CFLY and CVCPOUT can be removed. The pins CP, CN and VCP should be left open and keep

Rcp1_1

Effective Charge Pump

Output Resistance (Open

Loop, fclk = 1MHz)

1:1 Mode; VBAT

= 3.6V

2.5

Ω

Rcp1_2

1:2 Mode; VBAT

= 3V

fclk Accuracy

Accuracy of Clock

Frequency

-10

Vcurr_source

LED1 - CURR4 current

source dropout voltage

If the voltage drops below this threshold, the charge

pump will use the next available mode

(1:1 -> 1:2)

0.2

Isoft_start

Current limit for soft start

feature

400

tdeb

CP automatic up-

switching debounce time

cp_start_debounce=0

cp_start_debounce=1

200

Table 6. Charge Pump Characteristics

Symbol

Parameter

Condition

Min

Typ

Max

Unit

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