ZHCSE87A October 2015 – September 2023 DLPA3000
PRODUCTION DATA
The DLPA3000 illumination driver LED outputs are protected against open circuit use. In case no LED is connected and the DLPA3000 device is instructed to set the LED current to a specific level, the LED voltage (ILLUM_A_FB) will quickly rise and potentially rail to VIN. This should be prevented. The OVP protection circuit triggers once VLED crosses a predefined level. As a result the DLPA3000 is switched off.
The same protection circuit is triggered in case the supply voltage (VINA) will become too low to have the DLPA3000 work properly given the VLED level. This protection circuit is constructed around a comparator that will sense both the LED voltage and the VINA supply voltage. The fraction of the VINA is connected to the minus input of the comparator while the fraction of the VLED voltage is connected to the plus input. Triggering occurs when the plus input rises above the minus input and an OVP fault is set. The fraction of the VINA must be set between 1 V and 4 V to ensure proper operation of the comparator.
In general an OVP fault is set when
VLED/VLED_RATIO ≥ VINA/VINA_RATIO | ||
thus when: | ||
VLED ≥ VINA × VLED_RATIO/VINA_RATIO. |