ZHCSE88A October 2015 – February 2023 DLPA3005
PRODUCTION DATA
The DLPA3005 illumination driver LED outputs are protected against open circuit use. In case no LED is connected and the DLPA3005 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 DLPA3005 is switched off.
The same protection circuit is triggered in case the supply voltage (VINA) will become too low to have the DLPA3005 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.
The fraction of the ILLUM_A_FB voltage is set by the register VLED_OVP_VLED_RATIO, while the setting of the fraction of the VINA voltage is done by register VLED_OVP_VIN_RATIO. In general, an OVP fault is set when:
VLED/VLED_RATIO ≥ VINA/VINA_RATIO | ||
thus when: | ||
VLED ≥ VINA * VLED_RATIO/VINA_RATIO. |
Clearly, the OVP level is ratio-metric; that is, can be set to a fixed fraction of VINA.