ZHCSFP2B October 2016 – September 2021 TPS3850
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
8.2.2.2.4 Calculating the Sense Resistor
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
- VITN is the monitored falling threshold voltage and
- VIT(ADJ) is the threshold voltage on the SENSE pin
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
- VITN is the falling monitored threshold voltage
- VIT(ADJ) is the sense voltage threshold and
- ISENSE is the sense pin current
The calculated tolerance on R1 and R2 is 1%.