ZHCSL07C September 2019 – August 2021 TPS8802
PRODUCTION DATA
Each of the LED anodes must have enough voltage to forward bias the LED, regulate the CSA and CSB voltage, and exceed the driver dropout voltage requirement from DINA to CSA and DINB to CSB. A typical IR LED at 100 mA has 1.5-V forward voltage. The LED driver dropout voltage at 100 mA is 300 mV. With the CSA voltage set to 100 mV, the dropout voltage of 300 mV, and forward voltage of 1.5 V, at least 1.9 V must be applied to the IR LED anode for current regulation. Connect the IR LED anode to the LEDLDO. Enable the boost converter set to 2.7 V and enable the LED LDO to charge the IR LED anode capacitor. Alternatively, the IR LED anode can be connected to PLDO through a diode.
A typical blue LED at 50 mA has 4 V forward voltage. For the blue LED, the CSB voltage is 340 mV, the dropout voltage is 300 mV, and the forward voltage is 4 V. Supply over 4.64 V to the anode for the duration of the LED pulse. With a 47 µF capacitor derated to 30 µF, 100 µs LED pulse, the anode voltage drops by 170 mV. Thus, the capacitor must be charged to 4.81 V. Enable the boost converter set to 6 V and enable the LED LDO to charge the blue LED anode capacitor. The LED LDO has a diode voltage drop between the VBST voltage and LEDLDO voltage. The LEDLDO prevents the DINA pin from exceeding its recommended operating limit of 11.5 V.