How to increase Vref to 4.5 Volts in 16F628

[arunb]

Hi,

Compiler: PCM
MCU : PIC 16F628
ADC : MCP 3208

I am using the RA2 pin in the PIC 16F628 mcu to generate a Vref voltage for a MCP 3208 ADC.

I tried to increase the voltage level to about 4.5 Volts , but I find that the maximum I could get
was 2 Volts

The settings I used are as follows

setup_comparator(NC_NC_NC_NC);
setup_vref(VREF_HIGH | 0x12 |VREF_A2);

I tried this also
setup_vref(VREF_HIGH | 0x12 |VREF_A2);


I would like to know whether the above technique is OK and also how I can increase the voltage level to 4.5 V


Thanks
arun

[drh]

You probably need to buffer the Vref output. It has limited drive capability. So says the data sheet.
_________________
David

[PCM programmer]

[Humberto]

Hi arunb,

If you are using the MCP3208 12 bit ADC, what you need is 4.096V
as reference voltage, to get a round step of 1mV in LSB. Not 4.5V


best wishes,

Humberto

[arunb]

Hi,

Thanks for the help. I realised that a buffer would be needed. I anyway connected an external Vref source to the ADC.

By the way what Vref value is suitable???

thanks
arun

[Mark]

[Humberto]

[arunb]

Hi,

Thank you Humberto. I will definitely check it out..

cheers
arun