Help me connect a zener diode on the power supply pin of adc mcp3202

[vicky29]

hi
i want to connect a zener diode on the power supply pin of adc mcp3202. can anybody plz help me out for how to connet it. i am supplying 5 volts to adc.
do i need some resistance in series with diode or wht...plz help me out.

 

[polymath]

Re: zener on adc

Hi vicky29

I presume that you wish to connect the zener to provide a supply/reference voltage to pin 8 Vdd/Vref. Do not bother!

In my experience zeners have poor stability, high noise, a significant output slope and the first component to suspect when things go wrong.

As the MCP3202 only requires 550µA @ 5v, I would suggest you use a 3pin voltage reference IC to supply the device eg. MCP1542 or similar.

You will get better results with less effort.

hope this helps ...Polymath

 

[IanP]

Re: zener on adc

Maybe you should really look at other solutions such as 3-pin voltage regulators - 78L05, for example, which provide higher level of voltage regulation but, as a reference, here is how you use zener diodes:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2

Regards,
IanP

 

[yousafzai]

Re: zener on adc

instead of using a zener try LM336-2.5 for 2.5 volt reference and LM336-5 for 5 volts reference. it is more stable than an ordinary zener.

 

[azaz104]

Re: zener on adc

Hey guys,


can I ask a question, I am using the new Ti instrument CC2430, based on the 8051 MCU.
I want to do the same, i mean put an external voltage reference on pin 7, the thing is that it has an internal resistance of zero!
every time I connect the voltage source, it shorts out!!
what should I do ?

 

[vigneshwara_s]

Re: zener on adc

Hey guys,


can I ask a question, I am using the new Ti instrument CC2430, based on the 8051 MCU.
I want to do the same, i mean put an external voltage reference on pin 7, the thing is that it has an internal resistance of zero!
every time I connect the voltage source, it shorts out!!
what should I do ?

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Dear Azaz ,

I went through the datasheet of the IC . Pin Number 7 is the DVdd it specifies ,
And It would never be internal resistance of zero .
Please verify the correct pin number you fed the input and get back.

Regards,

S.Vigneshwaran.,
Spectrum Electra Technologies,
Chennai - 92.

 

[millwood]

zener on adc

zeners wouldn't be a good choice for voltage reference here. they can swing materially to render a 8-bit or 10-bit adc useless.

I would use a bandgap or a high precision voltage reference chip if you are working on a 10-bit or higher adc.