ZHCSFY8B January 2017 – September 2021 TPS3850-Q1
PRODUCTION DATA
There are three key specifications to keep in mind when calculating the resistor divider values (R1 and R2, see Figure 7-4 or Figure 8-3): voltage threshold (VIT(ADJ)), resistor tolerance, and the SENSE pin current (ISENSE). To ensure that no accuracy is lost because of ISENSE, the current through the resistor divider must be 100 times greater than ISENSE. Starting with R2 = 80.6 kΩ provides a 5-µA resistor divider current when VSENSE = 0.4 V. To calculate the nominal resistor values, use Equation 16:
where
Solving Equation 16 for R1 gives the nearest 1% resistor of 51.1 kΩ. Now, plug R1 back into Equation 16 to get the monitored threshold. With these resistor values, the nominal threshold is 0.65 V or 6.6%.
To calculate the minimum and maximum threshold variation including the tolerances of the resistors, threshold voltage, and sense current, use Equation 17 and Equation 18.
where
The calculated tolerance on R1 and R2 is 1%.