AVCC in a BLDC Controller

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Hai everyone

Iam designing a bldc controller. My motor voltage is 12V. According to application note AN444, Vcc is scaled down and used as reference. So i had designed a voltage divider for that.

Now what should i do with AVCC pin?

Nandhu

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nandhu015 wrote:
So i had designed a voltage divider for that.
Assuming that you really meant Vcc (and not Aref) this is almost certainly not a good idea. Use a regulator (linear or switching). They're inexpensive and designed for that purpose.

nandhu015 wrote:
Now what should i do with AVCC pin?
First step: read the datasheet. You'll probably find that AVcc powers the analog section (ADC, analog comparator) and also powers the digital I/O pins that are coincident with the analog input pins. If you aren't using any of the analog functions you can just connect AVcc to Vcc. If you are using the analog components, a filter circuit is recommended in the datasheet along with some advice on ground planes.

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net

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Quote:
Assuming that you really meant Vcc

Sorry for not giving sufficient info. I ment the motor voltage. i.e. 12V.

In the application note AN444

Quote:

The zero-crossing happens when the floating phase crosses the average voltage of the two supply rails. In this application note, it is assumed that the negative supply is at ground level, which makes the zero-cross voltage half the motor supply voltage. This dependence on motor supply voltage makes it impractical to use a fixed zero cross voltage threshold. Instead, the motor supply voltage (or scaled down version) is used as ADC reference voltage. The motor supply voltage needs to be low pass filtered before it is fed to the ADC. The VD/LPF of Figure 6 should be used for this purpose. The DC gain should be selected so that the voltage will be in the allowable range for the ADC, between 1.0V and AVCC.The zero-crossing happens when the floating phase crosses the average voltage of
the two supply rails. In this application note, it is assumed that the negative supply is at ground level, which makes the zero-cross voltage half the motor supply voltage. This dependence on motor supply voltage makes it impractical to use a fixed zero cross voltage threshold. Instead, the motor supply voltage (or scaled down version) is used as ADC reference voltage. The motor supply voltage needs to be low pass filtered before it is fed to the ADC. The VD/LPF of Figure 6 should be used for this.

Now what should i do with the AVCC pin? Shall i connect VCC to that?

Nandhu

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nandhu015 wrote:
Now what should i do with the AVCC pin? Shall i connect VCC to that?
Yes, assuming that you're not using the ADC or analog comparator. Otherwise, read the datasheet and do what it says.

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net