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PChav.1
PChav.1
Associate
February 2, 2021
Solved

How to calculate Vsense for VN5e010ah? any supporting document to calculate Rsense, Vsense and diagnostics?

  • February 2, 2021
  • 4 replies
  • 1470 views

I have gone through the vn5e010ah datasheet but it will not explain about the formula to calculation of Vsense , Rsense with respect to load current.

This topic has been closed for replies.
Best answer by Peter BENSCH

Please don't get confused by the fact that it seems like different factors need to be selected. In table 9 all conditions and the min/type/max values are listed:

  • K0 @ IOUT = 0.25 A; VSENSE = 0.5 V
  • K1 @ IOUT = 6 A; VSENSE = 0.5 V
  • K2 @ IOUT = 10 A; VSENSE = 4 V
  • K3 @ IOUT = 25 A; VSENSE = 4 V

So you will get the row with K2 for your max current of 10A.

In figure 9 you will see the tolerance band for the different load currents. The factors K0...K3 just relate to the X axis: 0.25A/6A/10/25A.

Please keep in mind: the tolerance is heavily dependent on the load current and temperature, e.g. for the current range of K2 the tolerance is +/-11%.

Over the temperature range of -40...150°C, a load current of 10A and with an Rsense of 1100 ohms you can expect a factor of 5850...7690 (Table 9, K2), resulting in a Vsense of 1.88V...1.43V.

This would result in an ADC value of around 0x181...0x125 at which you could disable the driver if you are using a 10 bit ADC with a voltage range of 5V.

Rule of thumb for measurements with ADCs: The lower the maximum voltage on the shunt (Rsense) in relation to the maximum voltage of the ADC, the lower the resulting accuracy.

All right now?

/Peter

4 replies

Peter BENSCH
Peter BENSCH
ST Technical Moderator
February 2, 2021

Rsense needs to be matched to the voltage range of your ADC that is measuring voltage Vsense, usually 5V in automotive applications.

Isense is a fraction of the load current, expressed by a factor Kx (datasheet, table 9, K0...K3). Unfortunately, there are physical restrictions that make this factor dependent on the load current and temperature (datasheet, fig. 9).

The load current divided by this factor creates Vsense over Rsense (when CS_DIS is not active and the current sensing pins are disabled).

When your question is answered, please close this topic by choosing Select as Best. This will help other users find that answer faster.

Good luck!

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
PChav.1
PChav.1Author
Associate
February 2, 2021

Thanks for reply,

In table 9 , I have few questions:

In my case, I use Rsense of 1.1K, Output Maximum current 10A at 8.5V source.

1) How can I select the factor out of K0, K2 and K3? I want to cut the output if current exceeds 10A by reading CS pin voltage through ADC (10 bit).

Peter BENSCH
Peter BENSCHBest answer
ST Technical Moderator
February 2, 2021

Please don't get confused by the fact that it seems like different factors need to be selected. In table 9 all conditions and the min/type/max values are listed:

  • K0 @ IOUT = 0.25 A; VSENSE = 0.5 V
  • K1 @ IOUT = 6 A; VSENSE = 0.5 V
  • K2 @ IOUT = 10 A; VSENSE = 4 V
  • K3 @ IOUT = 25 A; VSENSE = 4 V

So you will get the row with K2 for your max current of 10A.

In figure 9 you will see the tolerance band for the different load currents. The factors K0...K3 just relate to the X axis: 0.25A/6A/10/25A.

Please keep in mind: the tolerance is heavily dependent on the load current and temperature, e.g. for the current range of K2 the tolerance is +/-11%.

Over the temperature range of -40...150°C, a load current of 10A and with an Rsense of 1100 ohms you can expect a factor of 5850...7690 (Table 9, K2), resulting in a Vsense of 1.88V...1.43V.

This would result in an ADC value of around 0x181...0x125 at which you could disable the driver if you are using a 10 bit ADC with a voltage range of 5V.

Rule of thumb for measurements with ADCs: The lower the maximum voltage on the shunt (Rsense) in relation to the maximum voltage of the ADC, the lower the resulting accuracy.

All right now?

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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