7.3.5.5 Low-Dropout Operation

When the supply voltage drops below LED string total forward voltage plus V_(DROPOUT) at required current, the TPS92613-Q1 device operates in low-dropout conditions to deliver current output as close as possible to target value. The actual current output is less than preset value due to insufficient headroom voltage for power transistor. As a result, the voltage across the sense resistor fails to reach the regulation target.

If the TPS92613-Q1 is designed to operate in low-dropout condition, and the open-circuit diagnostics must be disabled by pulling the DIAGEN pin voltage lower than V_IL(DIAGEN). Otherwise, the TPS92613-Q1 detects an open-circuit fault and reports a fault indication on the FAULT pin. The DIAGEN pin is used to avoid false diagnostics due to low supply voltage.

In low-dropout operation, a diode in parallel with the sense resistor is recommended to clamp the voltage between SUPPLY and IN (across the sense resistor) in case of a large current pulse during recovery.