AS3682

Data Sheet

Charge Pump

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Revision 2.21

11 - 43

8 Detailed Functional Descriptions

8.1 Charge Pump

The AS3682 charge pump uses two external flying capacitors to generate output voltages higher than the battery volt-

age.

The charge pump can operate in three different modes:

!

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 1.5 times the battery voltage (without load)

- Battery current = 1.5 times output current

!

1:2 Mode

- The output voltage is 2 times the battery voltage (without load)

- Battery current = 2 times output current

8.1.1 Intelligent Adaptive Mode Switching (IAMS)

lowest internal power dissipation. The AS3682 examines the voltage at each current sink and automatically switches

into a higher charge pump mode; the switch-down procedure is achieved after the AS3682 performs analog signal pro-

cessing of all relevant parameters: the battery voltage, the actual charge pump voltage, the load current, and the resis-

tance of the next charge pump mode. By predicting the efficiency of the next state, the AS3682 will accurately

determine the switching point.

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 Open LED Detection

The voltages at the current sinks are used to determine the mode switching of the charge pump up, thus an open wire

to the LED could lead to a to high-power dissipation of the circuit.

The AS3682 scans and compares all voltages on the current sinks continuously, so that if the charge pump is already

at 1:2 mode and the required current cannot be provided, the circuit stops that current sink sensing until the next

information on the failing path from the GPIO_output (page 31) register.

Scanning occurs automatically upon first entering 1:2 mode.