Zxld1322 – Diodes ZXLD1322 User Manual
Page 12
ZXLD1322
ZXLD1322
Document number: DS32166 Rev. 3 - 2
12 of 17
April 2010
© Diodes Incorporated
A Product Line of
Diodes Incorporated
The TADJ pin of the device has a voltage threshold of 75mV nominal, which is derived from the reference voltage V
REF
. If
the voltage (V
TADJ
) on the TADJ pin is held above the threshold, the thermal compensation current will be zero and no
thermal compensation is applied. However, if VT
ADJ
falls below the threshold, a thermal compensation current (ITC) is
produced that is proportional to V
TADJ
. ITC is injected into the control loop in such a way as to reduce the demand current
I
ADJ
, causing the control loop to decrease the LED current. The LED current will be reduced to less than 10% of the set
value when V
TADJ
falls below 50mV.
The threshold voltage has been chosen to set a nominal threshold of 105°C and the device has been optimized to operate
with a standard 103KT1608 thermistor and 5k resistor in the potential divider. Circuit details are given in the application
notes. Alternative thermistor/resistor networks can be used providing the input resistance presented to the device at the
TADJ pin is similar at the threshold temperature. If no LED thermal compensation is required, the TADJ pin should be
connected to V
REF
to disable this function.