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AS3647/47B

Datasheet, Confidential - D e ta i l e d D e s c r i p t i o n

Flash Current Reductions

TXMASK

Usually the flash current is defined by the register led_current . If the TXMASK/TORCH input is used and (configured

by ext_torch_on=01), the flash current is reduced to flash_txmask_current if TXMASK/TORCH=1.

Current Reduction by VIN measurements in Flash Mode

Due to the high load of the flash driver and the ESR of the battery (especially critical at low temperatures), the voltage

on the battery drops. If the voltage drops below the reset threshold of the system would reset. To prevent this condition

the AS3647/47B monitors the battery voltage and keeps it above vin_low_v_run as follows:

Before a flash is started the voltage on VIN is measured. If the voltage is below the setting of vin_low_v the fault_uvlo

(see page 27) is set and the flash is disabled (driver stays in shutdown) if vin_low_v_shutdown=1. The flash current is

reduced to flash_txmask_current if vin_low_v_shutdown=0.

XX

10, 01

or 11

0

standby

0

XX

00

X

ext_torch_on (see page

24) not 10

0X

ext_torch_on =10

1X

ext_torch_on =10

external torch mode

LED current is defined

by the 7LSB

led_current

XX

01

1

indicator mode or

low current pwm mode

3

LED current is defined

by the 6LSB bits (bits

5...0) of led_current pwm

modulated with

31.25kHz defined by

register inct_pwm (1/

16...4/16)

X

X

10

1

assist light mode

LED current is defined

by the 7LSB

of led_current

XX

11

1

strobe_on (see page 27)

= 0

flash mode;

flash duration defined by

flash_timeout (see page

26)

LED current is defined

by led_current - the

current can be reduced

during flash, see Flash

Current Reductions

below

X0->1

strobe_on = 1 and

strobe_type (see page

27) = 0

X1

strobe_on = 1 and

strobe_type = 1

flash mode;

flash duration defined by

STROBE input; timeout

defined by flash_timeout

2. The MSB bit of this register not used to protect the LED; therefore the maximum assist / torch light current = half

the maximum flash current

3. The low current mode is a general purpose PWM mode to drive less current through the LED in average, but

keep the actual pulsed current in a range where the light output from the LED is still specified. As only the 6

LSBs of led_current are used the maximum current is limited to 1/4 of the maximum flash current.

Table 5. Operating Mode and current settings (Continued)

AS3647/47B configuration

operating mode and currents

mode_

setting

(see

page

26)

out_on

(see

page

26)

Condition

Mode

LED_OUT1/2

output current