AS3649

Datasheet - Detailed Descr i p ti on

www.ams.com/AS3649

1.0-2

14 - 39

8.4.5 Flash Timeout

If the flash is started a timeout timer is started in parallel. If the flash duration defined by the STROBE input (strobe_on=1 and strobe_type=1,

current sources (on pin LED_OUT1/2) are disabled (ramping down) and fault_timeout is set.

If the flash duration is defined by the timeout timer itself (strobe_on = 0, see Figure 23 on page 17), the register fault_timeout is set after the flash

has been finished.

8.4.6 Supply Undervoltage Protection

default state.

8.4.7 NTC - Flash LED Overtemperature Protection

The ntc_on (see page 25)=1, the flash LED is protected by the AS3649 using an internal comparator connected to NTC and an current source

DCDC is stopped, the current sources are disabled (instantaneous) and the bit fault_ntc (see page 28) is set.

As the external NTC cannot measure the LED temperature in real time during a high current flash pulse (the duration from heating up of the LED

until the NTC recognizes a too hot LED is usually too long), it is advisable to measure the LED temperature before the flash pulse (with the ADC

(see page 19) and ntc_current (see page 25)) and judge how much current can be driven through the LED (to be estimated depending on LED

heat sink and is usually specified by the LED manufacturer).

8.5 Operating Mode and Currents

The output currents and operating mode currents are selected according to the following table:

Table 5. Operating Mode and Current Settings

AS3649 Configuration

Operating Mode and Currents

mode_s

etting

(see

page 26)

Condition

Mode

LED_OUT1/2

Output current

XX

X

X

Shutdown

All registers are reset to their

default values

0

XX

00

txmask_torch_mode (see page

23) not 10

standby

0

0X

txmask_torch_mode =10

1X

txmask_torch_mode =10

external torch mode

LED current is defined by the 6LSB

1

bits of led_current1 and led_current2

XX

01

indicator mode or

low current pwm mode

2

LED current is defined by the 6LSB

bits (bits 5...0) of led_current1 and

led_current2 pwm modulated defined

by register inct_pwm

(31.5kHz: 1/16...4/16) or 7.9kHz: 1/

64...3/64)

X

X

10

torch light mode

LED current is defined by the 6LSB

2

bits (5...0) of led_current1 and

led_current2

XX

11

strobe_on (see page 28) = 0

flash mode;

flash duration defined by

flash_timeout (see page 26) LED current is defined by led_current1

and led_current2 - the current can be

reduced during flash, see Flash Current

Reductions below

X0->1

strobe_on = 1 and strobe_type

(see page 28) = 0

X1

strobe_on = 1 and

strobe_type = 1

flash mode;

flash duration defined by

STROBE input; timeout

defined by flash_timeout