8.2.2.2 Configure the Device

The first step to program the INA236 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 305.17578 μA. The INA236 allows selection of the CURRENT_LSB to be up to 8 x larger than the

minimum LSB size. For this example a value of 500 μA is used. Applying Equation 1 to the Current_LSB and

selected value for the shunt resistor results in a shunt calibration register setting of 1280d (500h). 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 INA236 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 / 2.5 μV = 28800d (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.

Table 8-3. Register Values

Register

Contents

LSB Value

Calculated Value

Configuration (0h)

16679d (4127h)

—

—

Calibration (5h)

1280d (500h)

—

—

Mask/Enable (6h)

32768 (8000h)

—

—

Alert Limit (7h)

28800d (7080h)

2.5 μV/LSB

28800 × 2.5 μV = 0.072 V

Shunt Voltage (1h)

19200d (4B00h)

2.5 µV/LSB

19200 × 2.5 μV = 0.048 V

Bus Voltage (2h)

7500d (1D4Ch)

1.6 mV/LSB

7500 × 1.6 mV = 12 V

Current (4h)

12000d (2EE0h)

500 µA/LSB

12000 × 500 µA = 6 A

Power (3h)

4500d (1194h)

Current LSB x 32 = 16 mW/LSB

4500 × 16 mW = 72 W

Shunt Voltage and Current return values in two's complement format. In two's complement format a negative

value in binary is represented by having a 1 in the most significant bit of the returned value. These values can

be converted to decimal by first inverting all the bits and adding 1 to obtain the unsigned binary value. This value

should then be converted to decimal with the negative sign applied.

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SBOSA81 – MAY 2021

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