AS3649 datasheet(13/39 Pages) AMSCO

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AS3649

Datasheet - Detailed Descr i p ti on

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8.4.1 Overvoltage Protection

In case of no or a broken LED(s) at the pin LED_OUT1/2 and an enabled DCDC converter, the voltage on VOUT1/2 rises until it reaches

VVOUTMAX (overvoltage condition) and the voltage across the current source is below low_vds

7., the DCDC converter is stopped, the current

sources are disabled and the bit fault_ovp (see page 29)

8 is set9. In a dual LED configuration for the AS3649, if a single open LED is detected,

this LED is disabled, fault_ovp is set and the device continuous operation with the other LED.

Note: In PWM operating mode (mode_setting=01b), open LED detection is disabled (and fault_ovp is not set). The output voltage will never-

theless be kept below VVOUTMAX.

8.4.2 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 27.5mA (current_boost=0), 34.3mA (current_boost=1)

10,11(see Figure 18). If the voltage on the LED (VFLED = LED_OUT1/2)

stays below VLEDSHORT, the DCDC is stopped (as a shorted LED is assumed), the current sources are disabled and the bit fault_led_short

(see page 29) is set. In a dual LED configuration for the AS3649, if a single shorted LED is detected, this LED is disabled, fault_led_short is set

and the device continuous operation with the other LED.

Note: In PWM operating mode (mode_setting=01b), short circuit protection is disabled.

Figure 18. Short LED Detection

8.4.3 Overtemperature Protection

The junction temperature of the AS3649 is continuously monitored. If the temperature exceeds TOVTEMP, the DCDC is stopped, the current

sources are disabled (instantaneous) and the bit fault_overtemp (see page 29) is set (but the operating mode mode_setting is not changed). The

driver is automatically re-enabled

12 once the junction temperature drops below TOVTEMP-TOVTEMPHYST.

8.4.4 TXMASK event occurred

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

happened (pin TXMASK/TORCH=1), the fault register bit fault_txmask (see page 28) is set.

5. Applies for all faults except TXMASK event occurred

6. Except for TXMASK event occurred and Overtemperature Protection

7. If overvoltage is reached, but none of the low_vds comparator(s) triggers, VOUT1/2 is still regulated below VVOUT-

MAX

8. In indicator or low current PWM mode (mode_setting (see page 26)=01) the register fault_ovp is not set under an

overvoltage conditions. The output voltage is nevertheless kept below VVOUTMAX.

9. In constant voltage mode (5V generation, register bit const_v_mode=1) this fault is disabled.

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

11. The LED short circuit protection is disabled in indicator mode (or low current mode using PWM) (mode_setting on

page 26=01b)

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

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