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Need of 5V to 3.3V conversion for using the eQEP module?

Started by bluenova333 4 months ago8 replieslatest reply 4 months ago92 views

I am trying to run closed loop V/F control on an induction motor using the TI C2000 TMS320F28069M board. I need to sense the speed in order to develop a speed controller in Code Composer Studio. For that I am using a speed encoder and the eQEP module on the board. Now the speed encoder gives the Ch. A , Ch. B and Index signal in 5V magnitude. However, the F28069 can accept only 3.3V signals. 

Does that mean I need to step down the 5.5 V signals coming from the encoder to 3.3V before giving to the eQEP module on the board? If anyone has tried this please do respond. Thank you.

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Reply by tcfkatMarch 3, 2022

I would use resistors ... ;)

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Reply by mikethewireMarch 3, 2022

...in a potential divider?  Or maybe some 3.3v zeners

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Reply by CustomSargeMarch 3, 2022

2.2k / 3.3k takes 5 down to 3.333.. But also see if the encoder will run at 3.3. A lot of sensors have quite a PS range.    G.H. <<<)))

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Reply by KavuluriSriramMarch 4, 2022

Hello Bluenova,

C2000 is a very sensitive DSP controller. 

I Suggest using an Opto logic level converter. 

please refer to the below link for an example.

https://eckstein-shop.de/SparkFunLogicLevelConvert...

Thansk
Sriram.K

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Reply by tcfkatMarch 4, 2022

Hello Sriram,

these are not optos but Logic-Level MOSFETs which provide bidirectional level shifting as needed for I2C, based on Application Note AN97055 from Philips. Simple and efficient, but imho not needed here.

Best regards

Eric

AN97055_Philips.pdf

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Reply by KavuluriSriramMarch 4, 2022

Hello Eric,

Yes, you are right, it's not Optos. I am sure this can be used in the application for voltage level conversion. 

May be i didn't get your point of view. can you elaborate ??

Thanks
Sriram.K

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Reply by tcfkatMarch 4, 2022
Re Sriram,

I would use optos only if I need the isolation barrier. Also, standard optos can be real slow, unless you use fast optos. (The thread starter says nothing about speed.)

In this case here even a simple series resistor would be fine, as long as you respect the maximum clamp current of 2mA of each input. (Well assuming that the power consumption of the MCU is always higher so that there is no risk of "pulling" Vdd up via the clamp diodes!)

tms320f28069m_absolute-maximum-ratings_6

Better of course is a real divider as proposed by CustomSarge.


Best regards,

Eric

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Reply by bluenova333March 7, 2022

I directly used the 5V supply, seems that I had to connect the shield as well and add a filter at the input of DSP to get cleaner signals. But still do you suggest that I reduce the pulses to 3.3 V ?