DD313-4 Datasheet, PDF (10/15 Pages) Silicon Touch Technology Inc. – LED open circuit detection

DD313-4
Constant Current Setting
The maximum constant current for is determined by an external resistor, R_EXT, placed
between the REXT and GND pins. The R_EXT resistor value is calculated with the equation
below.
I_OUT (A) = V_REXT (V) / R_EXT (Ω)
where V_REXT is the internal reference voltage on the REXT pin (typical 0.65 V)
LED Open Detection
The DD313-4 can detect LED open circuit (LO) by comparing with open circuit
threshold when IOUT is on. LO will result in ALARAM signal pulled low. Figure 6 illustrates
LO detection circuit. The table below shows a truth table for LO.
LO
LED is not open circuit (VOUT > VLO)
LED is open circuit (VOUT < VLO)
Alarm
0
1
VLED
LO
Error
+ _VLO
Constant
Current
Figure 6. LED Open Circuit Detection Circuit
Thermal Alarm and Shutdown
The DD313-4 has an on-chip temperature sensor for thermal alarm (TA) and shutdown
(TS) protection. If the junction temperature of a device exceeds the thermal alarm threshold,
ALARM output will be set to high. If the junction temperature reaches to a TS threshold, the
device will turn off outputs with ALARM remaining high until the junction temperature falls
below thermal error hysteresis of TA threshold. If the junction temperature is lower than a
thermal error hysteresis of TA threshold, the device will turn back on automatically.
40V Adjustable Current Sink Linear LED Driver
Version:PRE.002
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