# Thread: Current Sensing with BTS7002 & BTS7008 parts

1. ## Current Sensing with BTS7002 & BTS7008 parts

Hi, Im planning on using the both the BTS7002-1 and the BTS7008-2 parts in a new design.
The data sheet is not that clear and I need to know the maximum voltage that will appear on the current sense pin (IS) as this connected to the ADC.
The VS rail will be 16V and Rsense = 1.2Kohms

Am I correct in assuming it will be a linear o/p on the IS pin up to the VS rail?
So in my design the ADC is limited to 3.3V ans so I will need to put this through a divider?

Also the calculated current (KILIS = IL/IS) so assume IL = 21A for the BTS7002 part?

My circuit is shown below:-

Any help would be most appreciated...

Thanks

2. Hi,

BTS7702 and BTS7708 do not belong to NovalithIC family.

According to the datasheet of BTS7702, the max. current appears at IS pin is IIS(SAT),Max = 15mA. If the Rsense is 1.2k, the max. voltage at IS pin will be 15mA * 1.2k. Therefore diode should be used to protect microcontroller. E.g. In case of fault the current at IS pin will be IIS(fault) = 10mA(max.). VIS = 10mA * 1.2k = 12V.

During normal operation, if max. load current is 21A, the max. current at IS pin will be IL/KILIS_min. = 21A/(22700*0.92) = 1mA. In this case the max. voltage at IS pin will be 1.2K*1mA=1.2V. Therefore for current measurement voltage divider is not needed. The external component is only needed to protect the ADC pin in case of fault. Besides RIS_PROT and Dz1 are also needed to protect the device during overvoltage, reverse polarity, loss of ground.

Your question will be answered by the expert of these devices there.

3. Hi many thanks for the reply.

Sorry for the questions but can you help with the following:-
Can you explain what you mean by "diode should be used to protect microcontroller" and where and how would this protect the uProc in my design?

And what is (22700*0.92), cant see this is in the data sheet?

Also what is the relationship between the voltage at the IS pin and the IL current?

Finally can you see any issues with my circuit for use with these parts?

Many thanks

4. Hi,

You can use a diode as shown in the figure below to make sure that the voltage at ADC pin won't exceed the max. rating:

22700 is the typical current sense ratio specified in the datasheet. And the min./max. is +/-8%. So the min. Kilis will be 22700 * 0.92. In this case you will get max. current at current sense pin:

The relationship between the voltage at the IS and the IL current is : VIS = IL/KILIS * Rsense

The device should be fine for your application. Please add some external components (e.g. diode) to protect the ADC pin of the microcontroller.

5. Hi, many thanks again for the reply, very useful.

Hopefully the new design will work without too many issues...

Regards

6. Hi Assume the zener diode should be a 3.3V part as in my application the ADC is limited to 3.3V?
The data sheet shows a 7V part?

Regards

7. The diode should not exceed the max. rating of the voltage at ADC pin. I think the diode in datasheet is specified for dedicate MCU.

Regards,

Jing

8. Hi, the diode in the datasheet is rated at 7V, which seems an unusual value as most uProc and ADC i/ps are 3.3V or 5V?
Regards
Ian

9. Hi,

The max. voltage of the input depends on the MCU you use. E.g. For Arduino Uno, the max. voltage of I/O pin is VCC+0.5V, it means for 5V supply the max. voltage at I/O pin is 5.5V. Please check the datasheet of the microcontroller you use.