TPS1HC100-Q1
ZHCSLK6A –JULY 2021 –REVISED DECEMBER 2021
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6 A
1 A
ISNSerr@1A = 6%
100 mA
ISNSerr@100mA = 10%
50 mA
ISNSerr@50mA = 15%
20 mA
ISNSerr@20mA = 25%
5 mA
0 A
ISNSerr@5mA = 75%
图8-1. Current-Sense Accuracy
The maximum voltage out on the SNS pin is clamped to VSNSFH, which is the fault voltage level. To make sure
that this voltage is not higher than the system can tolerate, TI has correlated the voltage coming in on the
DIAG_EN pin with the maximum voltage out on the SNS pin. If DIAG_EN is between VIH and 3.3 V, the
maximum output on the SNS pin is approximately 3.3 V. However, if the voltage at DIAG_EN is above 3.3 V,
then the fault SNS voltage, VSNSFH, tracks that voltage up to 5 V. Tracking is done because the GPIO voltage
output that is powering the diagnostics through DIAG_EN is close to the maximum acceptable ADC voltage
within the same microcontroller. Therefore, the sense resistor value, RSNS, can be chosen to maximize the range
of currents needed to be measured by the system. The RSNS value must be chosen based on application need.
The maximum usable RSNS value is bounded by the ADC minimum acceptable voltage, VADC,min, for the smallest
load current needed to be measured by the system, ILOAD,min. The minimum acceptable RSNS value has to
ensure the VSNS voltage is below the VSNSFH value so that the system can determine faults. This difference
between the maximum readable current through the SNS pin, ILOAD,max × RSNS, and the VSNSFH is called the
headroom voltage, VHR. The headroom voltage is determined by the system but is important so that there is a
difference between the maximum readable current and a fault condition. Therefore, the minimum RSNS value has
to be the VSNSFH minus the VHR times the sense current ratio, KSNS divided by the maximum load current the
system must measure, ILOAD,max. This boundary equation can be seen in 方程式1.
(VSNSFH –VHR) × KSNS / ILOAD,max ≤RSNS ≤VADC,min × KSNS / ILOAD,min
(1)
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