Testing the AFE4490

Mohammad Hosseini1

Other Parts Discussed in Thread: AFE4490

Hello,

I'm currently working on a pulse oximeter design using the AFE4490 for a school project. I am using the reference schematic provided for the AFE from the evaluation module.

After physically creating my circuit for the AFE4490, how would I go about testing it to make sure it is functioning correctly? I want to test the chip before interfacing it to my microcontroller. I want to make sure first that there are no issues with the chip or my circuit.

What should I measure and at which pins? Do I need any special equipment?

Thanks!

over 11 years ago

0 Mohammad Hosseini1 over 11 years ago

Intellectual 610 points

Just bumping this up to hopefully get a response.

0 Praveen Aroul over 11 years ago

TI__Mastermind 49916 points

After ensuring the AFE power supplies are fine, you should measure the following:

a) 0.75V on TX_REF pin (pin#9)

b) 1V on BG pin (pin#7)

c) 0.9V on VCM pin (pin#4)

d) 4MHz clock on CLKOUT pin (pin#30) - assuming there is an external 8MHz crystal on XIN-XOUT pins.

You should be able to find this information in the AFE4490 datasheet.

0 Mohammad Hosseini1 over 11 years ago in reply to Praveen Aroul

Intellectual 610 points

Thanks Praveen. Yes I saw that same info on the datasheet. Wanted to make sure there was nothing else.

0 praba karan over 10 years ago in reply to Praveen Aroul

Prodigy 120 points

Hi Praveen,

I am working in a project with AFE4490 for pulse oximeter application. There are the values i am getting on the specified pins. are they are ok .. or do we have to do any changed in the hardware design.

a) 0.750V on TX_REF pin (pin#9)

b) .978V on BG pin (pin#7)

c) 0.912V on VCM pin (pin#4)

d) 4MHz clock on CLKOUT pin (pin#30) - We have an external 8Mhz oscillator connected to the board

Can you check the clock in the below image.. is it normal of do i have a problem with that.

0 Praveen Aroul over 10 years ago in reply to praba karan

TI__Mastermind 49916 points

Hello Praba,

The values you are getting from the BG, VCM and TX_REF are valid.

I think the waveform you are seeing on the scope has to do with the bandwidth of your scope and scope probe.
You will not see a square wave if your scope and scope probe is bandwidth limited to first few harmonics of 4 MHz.

0 HARINI B over 9 years ago in reply to Praveen Aroul

Intellectual 340 points

Hello Everyone,

Actually I am not getting 0.75Volts on TX_REF pin, after connecting to the Power Supply of 5V & 3.3V for AFE4490 Board.

Can I know the reason for this ?

And even when I change TX_REF through Programming on CONTROL2 Register, TX_REF Voltage is not changing @ all. It's coming with 0.66 V itself. Can

anyone help me on this ? I have attached the Schematic . Just go through it and let me know soon.

0 Praveen Aroul over 9 years ago in reply to HARINI B

TI__Mastermind 49916 points

I am unable to view your schematics.
Can you reattach the schematics?

0 HARINI B over 9 years ago in reply to Praveen Aroul

Intellectual 340 points

Here is the Schematic. Please have a look on it and let me know, what's the issue.

0 Amy Schnoor over 9 years ago in reply to HARINI B

TI__Mastermind 18285 points

Harini,

We are still not able to view the schematics. Can you try to use rich formatting?

0 HARINI B over 9 years ago in reply to Amy Schnoor

Intellectual 340 points

Hi,

Yup I am using "Rich Formatting" itself. But don't know, why it is not displaying after attaching it.

I have attached it once again. Let me know, whether it is visible.

0 Amy Schnoor over 9 years ago in reply to HARINI B

TI__Mastermind 18285 points

OK, I am still not able to view them. Try sending me or my colleague (Praveen Aroul) a private message with it attached.

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Testing the AFE4490