AS3661 datasheet(64/87 Pages) AMSCO

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AS3661

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

8.10.35 GAIN CHANGE CTRL

With hysteresis and timer bits the user can optimize the charge pump performance to better meet the requirements of

the application at hand. Some applications need to be optimized for efficiency and others need to be optimized for

minimum EMI, for example.

Note: Values above are typical and should not be used as product specification. Writing to TRESHOLD [7:6] bits by

the user overrides factory settings. Factory settings aren't user accessible.

Table 70. GAIN CHANGE CTRL Register

GAIN CHANGE CTRL

Bit

Bit Name

Default

Access

Bit Description

7:6

TRESHOLD

R/W

Bits set the threshold voltage at which the charge pump gain

changes from 1.5x to 1x. The threshold voltage is defined as

the voltage difference between highest voltage output (LED1

to LED6) and input voltage VBAT: VTRESHOLD = VBAT - MAX

(voltage on LED1 to LED6). If VTRESHOLD is larger than the set

value (100mV to 400mV), the charge pump is in 1x mode.

00: 400mV

01: 300mV

10: 200mV

11: 100mV

ADAPTIVE_

TRESH_EN

R/W

Gain change hysteresis prevents the mode from toggling back

and forth (1x -> 1.5x -> 1x...) , which would cause ripple on VIN

and LED flicker. When the adaptive threshold is enabled, the

width of the hysteresis region depends on the choice of

TRESHOLD bits (see above), saturation of the current

sources, charge pump load current, PWM overlap and

temperature.

0: Adaptive threshold disabled.

1: Adaptive threshold enabled.

4:3

TIMER

R/W

A forced mode change from 1.5x to 1.0x is attempted at the

interval specified with these bits. Mode change is allowed if

there is enough voltage over the LED drivers to ensure proper

operation. Set FORCE_1x to "1" (see below) to activate this

feature.

00: 5ms

01: 10ms

10: 50ms

11: infinite

FORCE_1x

Activates forced mode change. In forced mode charge pump

mode change from 1.5x to 1x is attempted at the interval

specified with the TIMER bits.

0: forced mode changes disabled.

1: forced mode changes disabled.

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