SLVSGP5 may 2023 TPS92629-Q1
PRODUCTION DATA
Step 1: Determine the current sensing resistor, R(SNSx) by using Equation 3.
where
According to design requirements, output current for the LED channel is 100 mA so that the calculated R(SNS) = 4.63 Ω and a 4.64 Ω resistor is selected.
Step 2: Design the current distribution between I(OUTx) and I(RESx), and calculate the current sharing resistor, R(RESx), by using Equation 4. The R(RESx) value actually decides the current distribution for I(OUTx) path and I(RESx) path, basic principle is to design the R(RESx) to consume appropriate 50% total power dissipation at typical supply operating voltage.
where
The calculated result for R(RES) resistor value is 108 Ω when V(OUTx) is typical 3 × 2.2 V = 6.6 V. A 107 Ω resistor is selected
Step 3: Design the threshold voltage of SUPPLY to enable the LED open-circuit, and calculate voltage divider resistor value for R1 and R2 on DIAGEN pin.
The maximum forward voltage of LED-string is 3 × 2.5 V = 7.5 V. To avoid the open-circuit fault or short-to-battery fault reported in low-dropout operation conditions, additional headroom between SUPPLY and OUTx must be considered. TheTPS92629-Q1 device must disable open-circuit and short-to-battery detection when the supply voltage is below LED-string maximum forward voltage plus V(OPEN_th_rising) and V(CS_REG). The voltage divider resistor, R1 and R2 value can be calculated by Equation 5.
where
The calculated result for R1 is 70.5 kΩ when V(OUTx) maximum voltage is 7.5 V and V(CS_REG) is 420 mV. A 70.6 kΩ resistor is selected