ZHCSL08C October 2019 – August 2021 TPS8804
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 LEDLDO and set LEDLDO_EN = 1 to charge the IR LED anode capacitor.
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. If the VCC voltage is between 5 V and 6 V, connect the blue LED anode to VCC through a 1-kΩ resistor. If VCC is between 6 V and 15 V, connect the blue LED anode to LEDLDO and set LEDLDO_EN = 1 to charge the blue LED anode capacitor. The LED LDO has a diode voltage drop between the VSLC voltage and LEDLDO voltage. The LEDLDO prevents the DINA pin from exceeding its recommended operating limit of 11.5 V.