INA745AIRELR datasheet(36/50 Pages) TI2

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An overcurrent threshold is set by programming the Current Over-Limit Threshold register (COL). Divide the

overcurrent limit value by the current LSB size to calculate the value needed to program the register.

In this example, the desired overcurrent limit threshold is 21A. The Current LSB size is 1.2mA/LSB, therefore the

value that must be programmed into Current Over-Limit (COL) register is 21A / 1.2mA/LSB = 17500d or 445Ch.

An overvoltage fault threshold on the bus voltage is set by programming the bus overvoltage limit register

(BOVL). In this example, the desired over voltage threshold is 16V. Divide the target threshold voltage by the

correct LSB value to calculate the value needed to program the register. For this example, the target value for

the BOVL register is 16V / 3.125mV = 5120d (1400h).

When setting the power over-limit value, the LSB size used to calculate the value needed in the limit registers is

256 times greater than the power LSB. This is because the power register is 24 bits in length while the power

fault limit register is 16 bits.

Values stored in the alert limit registers are set to the default values after VS power cycle events and must be

reprogrammed each time power is applied.

8.2.2.3 Calculate Returned Values

Multiply the returned value by the LSB value to calculate the parametric values. Table 8-4 below shows the

returned values for this application example assuming the design requirements shown in Table 8-3.

Table 8-4. Calculating Returned Values

PARAMETER

RETURNED VALUE

LSB VALUE

CALCULATED VALUE

Current (A)

15000d, 3A98h

1.2mA/LSB

18A

Bus voltage (V)

3840d, F00h

3.125mV/LSB

12V

Power (W)

900000d, DBBA0h

240µW/LSB

216W

Energy (J)

50625000d, 30479E8h

3.84mJ/LSB

194400J

Charge (C)

216000000d, CDFE600 h

75µC/LSB

16200C

Temperature (°C)

680d, 2A8h

125m°C/LSB

85°C

Current, Bus Voltage (positive only), Charge, and Temperature return values in 2's complement format. In a 2's

complement format, a 1 in the most significant bit of the returned value represents a negative value in binary.

These values can be converted to decimal by first iwnverting all the bits and adding 1 to obtain the unsigned

binary value. This value must then be converted to decimal with the negative sign applied.

8.2.3 Application Curves

Figure 8-3 and Figure 8-4 show the ALERT pin response to an overcurrent fault with a conversion time of 50μs

for the temperature, shunt voltage, and bus voltage measurements with averaging set to 1. This configuration

results in a total conversion time of 150μs for all three measurements. For these scope shots, persistence is

enabled on the ALERT channel to show the variation in the alert response for many sequential fault events. The

alert response time can change depending on the value of the current before fault occurs as well as the how

much the fault condition exceeds the programmed fault threshold. Figure 8-3 shows the response time for an

overcurrent fault when the fault condition greatly exceeds the programmed threshold, while Figure 8-4 shows

the overcurrent response time when the fault slightly exceeds the programmed threshold. Variation in the alert

response exists because the external fault event is not synchronized to the internal ADC conversion start. Also

the ADC is constantly sampling to get a result, so the response time for fault events starting from zero is slower

than fault events starting from values near the set fault threshold. In applications where the alert timing is critical

for overcurrent events, the worst-case alert response is equal to 2 × tconv_current + tconv_temp + tconv_voltage + 25μs.

An additional 25μs is added to allow for background math calculations. This equation does not account for the

1% oscillator tolerance and is only valid for cases where the overcurrent signal is greater than the conversion

threshold and noise. The measurement noise is a function of the conversion time. See Section 6.3.5.2 and

Section 8.1.2 for additional information.

Figure 8-4 shows a slightly longer worst case alert response because the alert threshold is within the noise band

of the device measurement and signal.

INA745A, INA745B

SBOSAC3B – JULY 2023 – REVISED AUGUST 2025

www.ti.com

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