for these registers is 16 times greater than the corresponding 20-bit LSB used in calculating returned values for

bus voltage and current.

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 42 A. The Current LSB size is 150 µA/LSB, therefore

the value that should be programmed into Current Over-Limit (COL) register the value is 40 A / (150 µA/LSB x

16) = 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 overvoltage threshold is 54 V. 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 = 17280d (4380h).

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

will be 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)

240000d, 3 A980h

150 µA/LSB

36 A

Bus voltage (V)

245760d, 3 C000h

195.3125 µV/LSB

48 V

Power (W)

3600000d, 36 EE80h

480 µW/LSB

1.728 kW

Energy (J)

202500000d, C11E7A0h

7.68 mJ/LSB

1.5552 MJ

Charge (C)

13500000d, CDFE60h

150 µC/LSB

32400 C

Temperature (°C)

10880d, 2A80h

7.8125 m°C/LSB

85°C

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

a two'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 inverting 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.

8.3 Power Supply Recommendations

The input circuitry of the device can accurately measure signals on common-mode voltages beyond the power-

supply voltage, VS. For example, the voltage applied to the VS power supply terminal can be 5 V, whereas the

load power-supply voltage being monitored (the common-mode voltage) can be as high as 85 V. Note that the

device can also withstand the full 0 V to 85 V range at the input terminals, regardless of whether the device has

power applied or not. Avoid applications where the GND pin is disconnected while device is actively powered.

8.4 Layout

8.4.1 Layout Guidelines

Place the required power-supply bypass capacitors as close as possible to the supply and ground terminals of

the device. A typical value for this supply bypass capacitor is 0.1 µF. Applications with noisy or high-impedance

power supplies may require additional decoupling capacitors to reject power-supply noise.

INA781

SBOSAC0 – JULY 2023

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