8.2.2.2 Configure the Device

The first step to program the INA234 is to properly set the device Configuration register (0h). On initial power

up the configuration register is set to the reset values as shown in Table 7-4. In the default power on state the

device is set to measured on the ±81.92 mV range with the ADC continuously converting the shunt and bus

(voltage at IN-) voltages. If the default power up conditions do not meet the design requirements, these registers

8.2.2.3 Program the Shunt Calibration Register

properly report any result based on current. The first step is to calculate the minimum LSB value for the current

by using Equation 2. Applying this equation with the maximum expected current of 10 A results in an minimum

LSB size of 4.8828125 mA. The INA234 allows selection of the CURRENT_LSB to be up to 8 x larger than the

minimum LSB size. For this example a value of 5 mA is used. Applying Equation 1 to the Current_LSB and

selected value for the shunt resistor results in a shunt calibration register setting of 2048d (800h). Failure to set

the value of the shunt calibration register will result in a zero value for any result based on current. Programming

this register is not required for reading shunt voltage, bus voltage, or setting alert limits.

8.2.2.4 Set Desired Fault Thresholds

The INA234 has the ability to assert the Alert pin on several different fault conditions as described in ALERT

Pin. The desired fault condition to assert the Alert pin needs to be selected by appropriately programming the

Mask/Enable Register (6h). Fault thresholds are set by programming the desired trip threshold into the Alert

Limit Register (7h).

For example, an over current fault condition would be selected by setting the SOL bit in the Mask/Enable

Register to 1. The desired threshold for the over current condition would have to be programmed in the Alert

Limit Register. In this example, the over current threshold is 9.0 A and the value of the current sense resistor is

8.0 mΩ, which give a shunt voltage limit of 72 mV. Once the shunt voltage limit is known, the value for the shunt

over voltage limit register is calculated by dividing the shunt voltage limit by the shunt voltage LSB size.

For this case, the calculated value of the alert limit register is 72 mV / 40 μV = 1800d (708). Since the bottom 4

bits of the shunt register are reserved the value programmed into the fault register must be left shifted by 4 or

multiplied by 16. This results in a final alert limit register value of 28800 (7080h)

reprogrammed each time power is applied.

8.2.2.5 Calculate Returned Values

Table 8-3 below shows the register values assuming the design requirements shown in Table 8-2. User

programmed values for the Configuration, Calibration, Mask/Enable and Alert limit registers are shown, as well

as, the returned values for shunt voltage, current, bus voltage and power. Parametric values are calculated by

multiplying the returned value by the LSB value.

Returned values for shunt voltage, current, and bus voltage need to be right shifted by 4, or divided by 16 to the

correct 12-bit value before multiplying by the LSB value. The shifting is needed because the bottom 4 bits in the

returned values are reserved and are always 0.

Table 8-3. Register Values

Register Name

Contents

Right Shifted 12 -

bit Value

LSB Value

Calculated Value

Configuration (0h)

16679d (4127h)

—

—

—

Calibration (5h)

2048d (800h)

—

—

—

Mask/Enable (6h)

32768 (8000h)

—

—

—

Alert Limit (7h)

28800d (7080h)

1800d (708h)

40 μV/LSB

1800 × 40 μV = 0.072 V

Shunt Voltage (1h)

19200d (4B00h)

1200d (4B0h)

40 µV/LSB

1200 × 40 µV = 0.048 V

Bus Voltage (2h)

7500d (1D4Ch)

468d (1D4h)

25.6 mV/LSB

468 × 25.6 mV = 11.98 V

Current (4h)

19200d (4B00h)

1200d (4B0h)

5 mA/LSB

1200 × 5 mA = 6 A

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SBOS844 – MAY 2021

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