AFE4490 LED Behavior

No, the LEDs will not light up when only power is supplied to the AFE.

The AFE registers have to be configured through the MCU to turn on the LEDs.

Best Regards.

Thanks Praveen. Without configuring the registers, should I be reading any specific voltages on the cathode/anode of the LEDs, when wired to the AFE?

No. The voltage level at the TXP and TXN pins will be zero without configuring the registers.

I'm actually getting 200 to 400 mV on these pins without configuring any registers. Any ideas why?

Have you created a complete PCB solution or have you built a breakout board for the AFE and hardwired the AFE connections to the MCU? Check if your connections to the device are correct.

Can you provide details like pictures, schematics of your hardware setup?

What voltages do you read at TXP and TXN pins when the LEDs are not connected to the AFE?

If you have an AFE4490EVM, can you compare the voltages on the EVM against your hardware setup?

Hi Praveen,

Apologies for the delayed response, I was busy with other projects.

1) I'm using a breakout board for the AFE chip in addition to a breadboard. Not the ideal solution of course, but I can't produce a complete PCB yet with my school's resources. The AFE is not wired to the MCU yet. See attached image.

2) See attached images for schematic and hardware.

3)

With LEDs connected: TXN = 0.7V and TXP = 0.7V

With LEDs disconnected: TXN = 0.75V and TXP = 0.75V

4) On the EVM I get about 2.2V on pins 14 and 15.

Hello Mohammad,

I do not find any issues with your schematics.

You may need to recheck your wire connections to the breakout board. It seems pretty daunting.

In one of your earlier posts, you mentioned that you were measuring 200 - 400 mV on the TXP and TXN pins.

In your previous post, you measured 700mV on those pins. 

Does the voltage on the TXP and TXN pins keep changing for every measurement?

Can you check the voltages on another breakout board?

Regards

Praveen.

Hello Praveen,

I ordered and soldered several more AFE4490 chips on breakout boards. I also checked the wire connections. As before, the reference voltage values and clock output (Pins 4, 7, 9, 30) show the expected values from the data sheet. However, I still read around 700 mV on the TXN and TXP pins with the AFE in its default state and no LEDs connected.

On the evaluation module, I read about 2.2V on TXN and TXP pins without the sensor connected to the board. With the sensor connected, I read around 4V on TXN and TXP.

So is the AFE4490 functioning correctly? I need to start collecting data, which means I need to connect to my MCU and move quickly to the firmware programming. Is this a serious issue, or can I ignore the 700mV on the TXN and TXP pins and proceed with the rest of my prototype and firmware development?

Thanks.

Hello Mohammad,

On the evaluation board, you read the voltages on the TX pins because the AFE is configured after power-up.

Since the reference voltage values and clock output show the expected values, you can connect the AFE to the MCU.

Moreover you can connecting the AFE digital interface to the MCU, so you shouldn't have any problem.

Hi, I have reproduced the same pattern on the breadboard, but I do not know if it works. At the moment I have not connected any microcontroller.

Could you tell me what are the basic connections, to turn on only the digital part of the chip? Moreover, when it is powered on pin 38, ClockOut, I should not see a square wave?

When i check the clockout on the eval i see the the square wave...

Can you help me? Thanks

Hello Gabriele,

Please refer to FAQ # 7 (link below) for AFE44xx sign of life after power up. 

http://e2e.ti.com/support/applications/high_reliability/f/30/t/369445.aspx

can you say to me the minimun connection to on this device?

for example, if i connect only the power supply and the clock, this device go in on? 

because in this method i can't see the clock on the pin 38.

thanks

perfect....thanks a lot!