MCP60x output swing

[Graham2107]

I am using a Microchip MCP602 to buffer and filter, with unity gain, for a 0-5Vdc clean DC input.

According to the spec sheet the out should swing Vss+100mV and Vdd-100mV but for a +5Vdc input I get only 4.25Vdc output. Range 0-4.25Vdc works 100%, above that is flat at 4.25Vdc.

I am using 0u1 across the IC and have tried others from a new batch of IC's with the same results. I have checked for noise and nothing is apparent,

What is going wrong here?

 

[ericgibbs]

I am using a Microchip MCP602 to buffer and filter, with unity gain, for a 0-5Vdc clean DC input.

According to the spec sheet the out should swing Vss+100mV and Vdd-100mV but for a +5Vdc input I get only 4.25Vdc output. Range 0-4.25Vdc works 100%, above that is flat at 4.25Vdc.

I am using 0u1 across the IC and have tried others from a new batch of IC's with the same results. I have checked for noise and nothing is apparent,

What is going wrong here?

Hi G,
Whats the output pin of the MCP6202 connected too.??
I use these on a 5V supply and I get within approx 100mV of +Vs, when connected to a Hi impedance load.

 

[Graham2107]

Hi G,
Whats the output pin of the MCP6202 connected too.??
I use these on a 5V supply and I get within approx 100mV of +Vs, when connected to a Hi impedance load.

Hi Eric

The output will go straight through to the A2D input of a PIC18F2523 but for now I am testing it either open circuit or into a 25K load as the spec sheet suggests to test for Vdd and Vss +/-100mV. Enclosed is image of SCH.

 

[MikeMl]

With 5V applied to the input, what does the first amplifier pull to?

 

[Graham2107]

Exactly the same voltage as I have mentioned i.e. Input1 = 5Vdc, Output1 = Input2 = 4.25Vdc = Output2

 

[MikeMl]

So go and buy a modern, rail-to-rail output opamp.

 

[Roff]

So go and buy a modern, rail-to-rail output opamp.

Are you saying that MCP604 is not a modern, rail-to-rail output opamp?

 

[Roff]

I am using a Microchip MCP602 to buffer and filter, with unity gain, for a 0-5Vdc clean DC input.

According to the spec sheet the out should swing Vss+100mV and Vdd-100mV but for a +5Vdc input I get only 4.25Vdc output. Range 0-4.25Vdc works 100%, above that is flat at 4.25Vdc.

I am using 0u1 across the IC and have tried others from a new batch of IC's with the same results. I have checked for noise and nothing is apparent,

What is going wrong here?

You did measure Vcc, didn't you?

 

[MikeMl]

Are you saying that MCP604 is not a modern, rail-to-rail output opamp?

Yep, although I should have said "So go and buy a modern, rail-to-rail input and output opamp"

Directly from the datasheet:

 

[Roff]

Yep, although I should have said "So go and buy a modern, rail-to-rail input and output opamp"

Directly from the datasheet:

Good find, Mike. Also, see the Input Common Mode spec in the datasheet.

 

[ericgibbs]

hi Graham,
When stated MCP60x... I incorrectly assumed you meant the MCP6002.....

 

[Graham2107]

Well found everyone, mystery solved. many thanks. It was actually very stupid of me not to see that in the DS

I will use MCP6041-42-44 in the future