INA229 datasheet(36/48 Pages) TI

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Table 8-3. Design Parameters (continued)

DESIGN PARAMETER

EXAMPLE VALUE

ADC Range Selection (VSENSE_MAX)

±163.84 mV

Temperature

25 ºC

Charge Accumulation Period

1 hour

8.2.2 Detailed Design Procedure

8.2.2.1 Select the Shunt Resistor

Using values from Table 8-3, the maximum value of the shunt resistor is calculated based on the value of

the maximum current to be sensed (IMAX) and the maximum allowable sense voltage (VSENSE_MAX) for the

chosen ADC range. When operating at the maximum current, the differential input voltage must not exceed the

maximum full scale range of the device, VSENSE_MAX. Using Equation 8 for the given design parameters, the

maximum value for RSHUNT is calculated to be 16.38 mΩ. The closest standard resistor value that is smaller than

the maximum calculated value is 16.2 mΩ. Also keep in mind that RSHUNT must be able to handle the power

dissipated across it in the maximum load condition.

RSHUNT <

VSENSE_MAX

IMAX

(8)

8.2.2.2 Configure the Device

The first step to program the INA229-Q1 is to properly set the device and ADC configuration registers. On initial

power up the CONFIG and ADC_CONFIG registers are set to the reset values as shown in Table 7-5 and

Table 7-6. In this default power on state the device is set to measured on the ±163.84 mV range with the ADC

continuously converting the shunt voltage, bus voltage, and temperature. If the default power up conditions do

not meet the design requirements, these registers will need to be set properly after each VS power cycle event.

8.2.2.3 Program the Shunt Calibration Register

The shunt calibration register needs to be correctly programmed at each VS power up in order for the device

to properly report any result based on current. The first step in properly setting this register is to calculate the

LSB value for the current by using Equation 3. Applying this equation with the maximum expected current of

10 A results in an LSB size of 19.0735 μA. Applying Equation 2 to the Current_LSB and selected value for the

shunt resistor results in a shunt calibration register setting of 4050d (FD2h). Failure to set the value of the shunt

calibration register will result in a zero value for any result based on current.

8.2.2.4 Set Desired Fault Thresholds

Fault thresholds are set by programming the desired trip threshold into the corresponding fault register. The list

of supported fault registers is shown in Table 7-1. Since the fault limit registers are 16 bits in length, the effective

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

values for bus voltage and current.

An over current threshold is set by programming the shunt over voltage limit register (SOVL). The voltage that

needs to be programmed into this register is calculated by multiplying the over current threshold by the shunt

resistor. In this example the over current threshold is 10 A and the value of the current sense resistor is 16.2 mΩ,

which give a shunt voltage limit of 162 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.

In this example, the calculated value of the shunt over voltage limit register is 162 mV / (312.5 nV × 16) =

32400d (7E90h).

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

(BOVL). In this example the desired over voltage threshold is 52 V. The value that needs to be programmed into

this register is calculated by dividing the target threshold voltage by the bus voltage fault limit LSB value of 3.125

mV. For this example, the target value for the BOVL register is 52 V / (195.3125 μV × 16) = 16640d (4100h).

INA229-Q1

SLYS024A – MAY 2020 – REVISED JUNE 2021

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