INA229 datasheet(34/40 Pages) TI

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IN+

IN-

VBUS

SCLK

MOSI

MISO

ALERT

GND

SHUNT

48 V

BATT

GND

10 k

100 nF

SPI

I/F

LOAD

CHARGER

S = 2.7 V to 5.5 V

MCU

Figure 8-2. INA229 High-Side Sensing Application Diagram

8.2.1 Design Requirements

The INA229 measures the voltage developed across a current-sensing resistor (RSHUNT) when current passes

through it. The device also measures the bus supply voltage and calculates power when calibrated. It also

comes with alert capability, where the alert pin can be programmed to respond to a user-defined event or a

conversion ready notification.

The design requirements for the circuit shown in Figure 8-2 are listed in Table 8-3.

Table 8-3. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Power-supply voltage (VS)

5 V

Bus supply rail (VCM)

48 V

Bus supply rail over voltage fault threshold

52 V

Average Current

6 A

Overcurrent fault threshold (IMAX)

10 A

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 Shunt resistor selection

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 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

INA229

SLYS023 – DECEMBER 2020

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