3.3 VDC ST7920 and CFAG module operation

[buckanear7]

I am interested in using one of the modules with the Sitronix ST7920 controller. Can any of the CFAG modules with the ST7920 chip at 3.3 VDC instead of 5 VDC? The one I am interested in is the CFAG14432D-TTI-TT.

I want to use it with 3.3 volt digital logic as I will be driving it from an FPGA. I know I can use level translation but want to keep controller board layout size down.

thanks

james

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[CF Support2]

The ST7920 is capable of operating with +3.3v logic and supply. Off the shelf, the module will need to be modified as the contrast driving circuit is optimized for +5v. Checking over my notes - I don't have the exact details of what needs changed but can get them for you.

If you are going to do any volume ordering, we can bring the module in set up for +3.3v operation.

 

[buckanear7]

At this time this is for hobby use and I need really only one.

Is is then possible to drive the VDD pin from 3.3 Volts and Vo from a 5 volt source?

james

 

[buckanear7]

looking at the specs it seems that I can operate the logic from 3.3 Volts and the Vo or Vlcd pin from 5 volts via a resistor divider.

My only concern then would be the Rf resistor value. If that is accessible from the backside of the module then it could be replaced to bring the oscillator into proper range and or current.

james

 

[CF Support2]

The controller can accept a +3.3v logic and supply. The module itself it optimized for a +5v supply. If you mix a +5v supply and a +3.3v logic, the controller may not see the 3.3v as a "high" and it won't work properly.

To set the module up for 3.3v operation require the removal of a component and then adding a jumper. We are verifying the jumper's connection at this point. We should have that information for you in the next couple of days.

I'm have a couple samples brought in just in case. We should have you up and running with a stock part modified well before then.

 

[CF Support2]

Sorry for the delay in getting back to you. To convert the CFAG14432D for 3.3v supply / logic, remove Q1 and replace with a 0 Ohm jumper as shown.