INA238: INA238 Current sensing

Hello Gaung, 

Thanks for quick support. 

We have captured some of Shunt voltages w. r. t current. 

Actual it shows difference in hardware level and Firmware level.    

We have also tried to measure the Bus Voltage and it is working too well, we are getting same bust voltage as per settled voltage. 

Let me know, what we are missing in the shunt voltages and Current Sense. 

Hi,

Can you loop the measurement many times, at say 430mA, and observe if the results are stable? At the same time, is the DVM reading stable? You can print out the shunt register values.

An alternative is to remove the shunt resistor and apply a voltage source to the inputs. Often times, it is easier to debug.

There is no pattern in the current data and it is hard to speculate what is causing the difference.

Regards, Guang  

Hello,

Yes. Results are stable & DVM reading are also stable.

We removed the shunt resistor and applied the voltage source and try to read the values, but we are continually getting same value.

below is our code  for VShunt, Current sense and Vbus

int i2c__ina_238_read_raw_data(uint32_t dev_add, uint8_t reg, uint16_t *read_data)
{
HAL_StatusTypeDef ret_status;
uint8_t read_buff[2] = {0};

ret_status = HAL_I2C_Mem_Read(&hi2c1,(dev_add << 1), (uint16_t) reg, 1, read_buff, 2, 100);
if(ret_status != HAL_OK) {
// uart__write("ERROR:: i2c__ina_238_read_raw_data failed\n\r");
return 0;
}
*read_data = (uint16_t)(read_buff[0] << 8) | (uint16_t)(read_buff[1]);
return 1;
}

int i2c__ina_238_write_data(uint32_t dev_add, uint8_t reg, uint16_t write_data)
{
HAL_StatusTypeDef ret_status;
uint8_t write_buff[2] = {0};
write_buff[0] = (write_data >> 8);
write_buff[0] = write_data;
ret_status = HAL_I2C_Mem_Write(&hi2c1,(dev_add << 1), (uint16_t) reg, 1, write_buff, 2, 100);
if(ret_status != HAL_OK) {
// uart__write("ERROR:: i2c__ina_238_write_data failed\n\r");
return 0;
}
return 1;
}

float curr;
i2c__ina_238_read_raw_data(0x40, INA_238_CURRENT, &raw_vltg);

if(raw_vltg > 0x7FFF) {
raw_vltg = (float)raw_vltg - 0x10000;
}
curr = raw_vltg * 0.0000006;

HAL_Delay(100);

i2c__ina_238_read_raw_data(0x40, INA_238_CURRENT, &raw_vltg);
if(raw_vltg > 0x7FFF) {
raw_vltg = (float)raw_vltg - 0x10000;
}
curr = raw_vltg * 0.000305;
HAL_Delay(100);

i2c__ina_238_read_raw_data(0x40, INA_238_VBUS, &raw_vltg);
if(raw_vltg > 0x7FFF) {
raw_vltg = (float)raw_vltg - 0x10000;
}
float vbus = (float) (0.003125) * raw_vltg;
HAL_Delay(100);

i2c__ina_238_read_raw_data(0x40, INA_238_V_SHUNT, &raw_vltg);
if(raw_vltg > 0x7FFF) {
raw_vltg = (float)raw_vltg - 0x10000;
}
float vshunt = (float)0.000005 * raw_vltg;
HAL_Delay(100);

We are able to read the Vbus value, only issue with current sense part.

Hi,
By “continually getting same value.”, do you mean the phenomenon is the same as before?
Can you step the input shunt voltage through a list of values and list side by side the actual Vshunt and the INA238 measurements?
Because current is simply calculated from Vshunt, we can focus on Vshunt for now and current will naturally follow.
Regards, Guang

Hello Guang, 

continually getting same value means we are getting same value 0 for any current. 

Now I have changed load and try to read Vshunt , we received same Vshunt value through firmware.

 still, we are not able to read current.

for current sense, is it really necessary to calculate SHUNT_CAL for current measurement?

We are trying to set the SHUNT_CAL register, but we are getting some garbage value.

Do you have any idea, what is the procedure SHUNT_CAL, write and read.