ZHCSME3 November 2020 TPS27SA08
PRODUCTION DATA
#GUID-CFB77F13-1DD7-409C-9BD9-57EBF838CCC6/SLVSDM44646 shows the requirements for the load current sense in this application. The KSNS value is specified for the device and can be found in the Specifications section.
| PARAMETER | EXAMPLE VALUE |
|---|---|
| Current Sense Ratio (KSNS) | 4600 |
| Largest diagnosable load current | 20 A |
| Smallest diagnosable load current | 50 mA |
| Full-scale ADC voltage | 5 V |
| ADC resolution | 10 bit |
The load current measurement requirements of 20 A ensures that current can be sensed up to the 20-A current limit, while the low level of 100 mA allows for accurate measurement of low load currents.
The RSNS resistor value should be selected such that the largest diagnosable load current puts VSNS at about 90% of the ADC full-scale. With this design, any ADC value above 90% can be considered a fault. Additionally, the RSNS resistor value should ensure that the smallest diagnosable load current does not cause VSNS to fall below 1 LSB of the ADC. With the given example values, a 1-k? sense resistor satisfies both requirements shown in #GUID-CFB77F13-1DD7-409C-9BD9-57EBF838CCC6/SLVSDM46020.
| LOAD (A) | SENSE RATIO | ISNS (mA) | RSNS (?) | VSNS (V) | % OF 5-V ADC |
|---|---|---|---|---|---|
| 0.050 | 4600 | 0.011 | 1000 | 0.011 | 0.22% |
| 20.000 | 4600 | 4.348 | 1000 | 4.348 | 87% |