ZHCSL07C September 2019 – August 2021 TPS8802
PRODUCTION DATA
Enough voltage must be provided to the LED such that the DINA voltage is at least the dropout voltage (VDINA,DROP) above the CSA voltage while the LED driver is enabled. Ensure the DINA voltage does not exceed 11.5 V. Because of the high LED drive currents, a large capacitor connected to the LED anode is required to provide pulsed power to the LED. Any of the internal regulators ( PLDO, LEDLDO) or external supply (VBAT, VDC) meeting the voltage requirements can be used to charge the LED capacitor. Depending on the LED forward voltage, the LED anode can be connected to the battery or to the LEDLDO. Do not connect the LED anode directly to VBST in low-power applications, because the boost converter output voltage can exceed the DINA absolute maximum.
The LED LDO clamps the VBST voltage and blocks reverse current with an integrated diode. It is current limited to prevent inrush current caused by charging the large capacitor. The regulation voltage is adjustable in the LEDLDO register. The LED LDO may be operated with VBST below the regulation voltage. In this case, the LEDLDO voltage stabilizes to VBST minus a diode voltage drop.
The LED driver current and rise time can vary by a few millivolts and microseconds across the LED anode supply and VCC voltages. It is recommended to use a consistent LED anode voltage whenever the LED driver is enabled. If the LEDLDO is used to supply the LED anode, ensure the boost converter is enabled to the same voltage whenever the LEDLDO is enabled.
Connect a capacitor with a value between 1 µF and 100 µF to the LEDLDO.