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# LMP92064: LMP92064

Part Number: LMP92064
Other Parts Discussed in Thread: INA148, INA301, INA300, INA231, ISO1541, TIDA-00313, INA226, TIDA-01608, ISOW7842, INA260, OPA333, TIDA-00528, TIDA-00332, INA138, AMC1100, AMC1200

Hi,

Greetings!

I am developing a control module to trigger the output, based on current sensing.

The sensing current is 45mA.  I was going through the data sheet of LMP920064 and i believe this device will sense the max current up to 15mA.

I have attached the block level approach of this requirement. can you please suggest and guide us the suitable device?

Regards,

Rajesh.

Sensor.pdf

• Hello Rajesh,

Thanks for the schematic. In order to provide you an optimal solution can you please answer the following questions?

1. What is the minimum current you need to measure?
2. What is the maximum current you need to measure?
3. What is the frequency of the source voltage? This seems to be your common-mode voltage if you plan to use a high-side configuration.
4. Do you want to measure current on the high (voltage source) side or low-side (underneath the load)?
4. Are you measuring DC current?
5. Do you need a digital output (I2C) current sensor?

I am not sure where you are getting the 15mA max current from, but how much current the LMP92064 can sense is dependent upon the shunt resistor chosen. Also please note that the LMP92064 is a low-side current sensing device. The common-mode voltage (VCM) at the input pins (INCP, INCN, INVP) cannot exceed VDD+0.3V without causing device damage thus this part is place at low-side where VCM is near 0V.

Sincerely,
Peter Iliya
Current Sensing Applications
• Hi Peter,

1. The minimum current is 10mA.

2. The Max current is 45  - 50 mA.

3.  Voltage 110V , 50Hz.

4. We  wanted to measure at typical / Mid level 110VAC, 44mA.

5.  This is AC current.

6. There should be a output pin, should trigger the relay, so that the relay will close to extend the supply.

Regards,

Rajesh.

• Hey Rajesh,

We do not have any current shunt monitors specifically able to withstand this 82.5V to 140V common-mode range. TI does have differential amplifiers which can function in the same way a current shunt monitor does. An example would be the +-200V common-mode INA148, which can have a max +-5mV offset. This would be just a linear analog output and you would have to program the trigger voltage/ADC reading of your MCU, or you would have to drive the output into a comparator which could drive a digital input of your MCU. I am not sure which method you are going for.

There are other methods to increase the common-mode voltage range of our current sensor amplifiers (CSA). I have attached reference designs showing how to do this. Overall you will have to power the CSA from the bus voltage (110V) and then isolate or level-shift the CSA output signals (digital or analog) so that they can interface/communicate with your MCU, which would be referenced to Earth/system ground.

These designs use a couple different parts, but if you choose to implement one of their strategies (e.g., floating the supply voltage), then specific devices for your application would be INA300 or INA231. The INA300 is cheaper because it is only a comparator output (ALERT pin) which works well if you only care about triggering the relay when the current exceeds the threshold. You set the threshold voltage with a resistor from LIMIT pin to GND pin. You also have ability to set a latch mode, where one over-current condition will keep the ALERT output high regardless of input. Please note that you would have to level shift or isolate the ALERT pin if you plan to float INA301 power supply with a Zener diode and drive the MCU.

The INA231 is the cheapest ALERT capable digital CSA. The ALERT can be programmed (via I2C) to trip for multiple conditions, but this would give you more flexibility in fine tuning the threshold voltage and internal averaging.

TIDA-00313: INA226 (Zener powered) + ISO1541
- This will provide most likely the best error since maximum input offset voltage (Vos) is +-10uV.
- Digital I2C output

TIDA-01608: INA260 (ISO powered) + ISOW7842
- For your case, you cannot use the INA260 because it has internal shunt resistor that can't accept more than 15A of continuous current, but this design shows how to use another high-voltage I2C isolator with one of our digital current sensing devices.
- Most of error will come from the INA260 (or whatever digital current sense amplifier is chosen).
- Digital I2C output

TIDA-00528: INA226 (MCU powered) + OPA333 (Zener powered) + Transistor
- This approach uses a precision operation amplifier to sense the current and level shift the sense current so INA226 can read and report it directly to MCU I2C bus.
- This approach will allow you to use a voltage-output current sensor (IN181 for example). You are not limited to the digital output devices here.
- The error here seems to be slightly higher compared to previous two designs since more analog components are needed.

TIDA-00332: INA138 (Zener powered) + Transistor
- This takes advantage of using our current-output amplifier and level-shifting the output using a transistor.
- Will have the highest error since INA138 has higher input offset votlages (Vos max = +-1mV) and gain error. The load resistor tolerance will also add error.

AMC1200/AMC1100
- These current sensor device includes the isolation barrier internally so minimal components needed.
- Has large offset comparitively (+-1.5mV Vos max), so this will be main contributor of error.

Hope this helps.

Sincerly,
Peter Iliya
Current Sensing Applications