SNVSBY7 March 2021 TPS92390
The TPS92390 boost DC/DC converter generates the anode voltage for the LEDs. During normal operation, boost output voltage is adjusted automatically based on the LED current sink headroom voltages. This is called adaptive boost control. The number of used LED outputs is set by LED_SET pin and only the active LED outputs are monitored to control the adaptive boost voltage. Any LED strings with open or short faults are also removed from the adaptive voltage control loop. The LED driver pin voltages are periodically monitored by the control loop and the boost voltage is raised if any of the LED outputs falls below the VHEADROOM threshold. The boost voltage is lowered until any of the LED outputs touch the VHEADROOM threshold. See Figure 7-4 for how the boost voltage automatically scales based on the OUTx-pin voltage, VHEADROOM and VHEADROOM_HYS.
The resistive divider (R1, R2) defines both the minimum and maximum adaptive boost voltage levels. The feedback circuit operates the same in boost and SEPIC topologies. Choose maximum boost voltage based on the maximum LED string voltage specification. Before the LED drivers are active, the boost starts up to the initial boost level. The initial boost voltage is approximately in the 88% point of minimum to maximum boost voltage. Once the LED driver channels are active, the boost output voltage is adjusted automatically based on OUTx pin voltages. The FB pin resistor divider also scales the boost OVP, OCP levels and the LED short level in HUD application.