AS3643 datasheet(13/34 Pages) AMSCO

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AS3643

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

Short Circuit Protection

After the startup of the DCDC converter, the voltage on LED_OUT1/2 is continuously monitored and compared against

VLEDSHORT if the LED current is above 20mA

7(see Figure 18). If the voltage across the LED (VFLED = VOUT1/2-

LED_OUT1/2) stays below VLEDSHORT, the DCDC is stopped (as a shorted LED is assumed), the current sinks are dis-

abled and the bit fault_led_short (see page 25) is set.

Figure 18. Short LED detection

Overtemperature Protection

The junction temperature of the AS3643 is continuously monitored. If the temperature exceeds TOVTEMP, the DCDC is

stopped, the current sinks are disabled (instantaneous) and the bit fault_overtemp (see page 25) is set. The driver is

automatically re-enabled

8 once the junction temperature drops below TOVTEMP-TOVTEMPHYST.

TXMASK event occurred

If during flash, TXMASK current reduction is enabled (see TXMASK on page 15, configured by ext_torch_on=01) and

a TXMASK event happened (pin TXMASK/TORCH=1), the fault register bit fault_txmask (see page 25) is set.

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, see Figure 25 on page 17) exceeds tFLASHTIMEOUT (adjustable by register flash_timeout (see

page 24)), the DCDC is stopped and the flash current sinks (on pin LED_OUT1/2) are disabled 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.

Supply undervoltage Protection

If the voltage on the pin VIN (=battery voltage) is or falls below VUVLO, the AS3643 is kept in shutdown state and all

registers are set to their default state.

Wakeup Circuit - Power off detection

In flash, assist light and indicator mode (register mode_setting (page 24)=01, 10 or 11) and out_on (page 24)=1, if SCL

is L for more than tTIMEOUT, shutdown mode is automatically entered. This feature automatically detects a power-off of

the controlling circuit driving SCL and SDA (VDD_I/F goes to 0V e.g. due to a low power condition of the driving circuit)

- the internal circuit is shown in Figure 19:

7. To avoid errors in short LED detection for LEDs with a high leakage current

8. In constant voltage mode (const_v_mode=1) the DCDC will not be automatically re-enabled.

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