SSL3250A datasheet(13/26 Pages) NXP

13 / 26 page

SSL3250A_3

Product data sheet

Rev. 03 — 30 June 2009

13 of 26

NXP Semiconductors

SSL3250A

Photo ﬂash dual LED driver

The four protection circuits and their bits in the status register are as follows:

• Overvoltage protection

• Time-out protection

• Overtemperature protection

• Output short protection

When a protection is triggered, switching of the IC is inhibited without a soft ramp-down of

the current in the main LED and also the indicator LED will be switched off.

To recover from this fault condition in I2C mode, write 00h to the current control register

(00h) to clear the status register release the INT line. After clearing the status register, the

current control register can be reloaded and the ﬂash can be retriggered. Reloading the

other registers is not necessary as they will not lose their value when an interrupt is

generated. In Direct enable mode the status register is cleared and the INT line is

released, by making both the EN1 and EN2 pins lO.

8.4.1 Overvoltage protection

If the output voltage (VO) exceeds its limit (Vovp, see Table 9), switching of the converter is

inhibited. The output voltage will exceed Vovp limit when no LEDs are connected between

pins VO and LED. In some cases an overvoltage protection may occur when the LED pin

is shorted to GND during the period a Flash is generated.

The converter is trying to compensate for the loss of feedback current by increasing VO.

When an overvoltage is encountered, the OVPtrig ﬂag (bit 0) is set in the status register.

8.4.2 Untimed Flash mode

To avoid overloading of the main LED during a ﬂash in Direct enable mode or I2C control

mode in untimed Flash mode (bit 4, TO_DEF = 0 in Timer control register 01h). A time-out

timer limits the maximum ON time of the ﬂash. In both control modes the ﬂash time-out

time is set to a ﬁxed level of 820 ms.

When the ﬂash strobe signal is set to LOW in I2C control mode, bit 0 in register 02h is

set to 0. When the EN1 signal is set to LOW before the time-out timer has expired in

Direct enable mode, the time-out timer is reset.

When a time-out situation is encountered, the TOtrig ﬂag (bit 1) is set in the status

8.4.3 Overtemperature protection

If the chip temperature exceeds its limit (Totp, see Table 9), switching of the converter is

inhibited until the temperature drops below its limit minus a small hysteresis.

When an overtemperature situation is encountered, the OTtrig ﬂag (bit 2) is set in the

status register.

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