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JackyCheung
JackyCheung
Associate III
September 28, 2014
Question

Bus Voltage Sensing Formula

  • September 28, 2014
  • 3 replies
  • 1057 views
Posted on September 28, 2014 at 16:21

Gigi:

         I'm in the Bus Voltage Sensing parameter settings of Workbench when the input voltage is 24V, I am a divider resistor R1 = 51K R2=1K, how to calculate excuse me my Bus voltage sensing network partitioning factor?

　Best Regards

　Jacky
This topic has been closed for replies.

3 replies

Gigi
Gigi
ST Employee
September 29, 2014
Posted on September 29, 2014 at 09:20

Ciao Jacky

Usually the Bus Voltage Sensing is done with a simple voltage divider.

Considering the one explained

http://en.wikipedia.org/wiki/Voltage_divider

 you have to compute the Vin/Vout ratio that depends only on the resistors network: Vin is the DC bus voltage and Vout is the input of the ADC of the micro.

In your case, I assume that the R2 is between Vout and ground.

Bus Voltage Sensing = (51K + 1K)/(1K) = 52

This mean that you are scaling 52 times the DC bus voltage -> 0.46V to ADC (exploiting small part of the range. Maybe the petitioning factor can be improved).

Ciao

Gigi 

JackyCheung
JackyCheungAuthor
Associate III
September 29, 2014
Posted on September 29, 2014 at 18:29

Thank you, the problem is solved.

mikemike9141
mikemike9141
Associate III
September 30, 2014
Posted on September 30, 2014 at 09:54

Hi Gigi,

I would like to comment on a possible improvement on that configuration item. I also stumbled on this for a moment because

- on other locations, the tool asks for a gain (for example, current sensing), which is more straight forward in my opinion.

- for the bus voltage, I can only enter an integer value. In my design, the attenuation factor isn't.

- in the resulting header file, this number is indeed converted into a (floating point) gain.

Regards

Frank

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