AFE4403: How to decrease or cutdown the short current of Photodiode in AFE4403?

Hi Matthew,

I don't completely understand the situation. Which pins are being shorted? Are TXN or TXP being shorted to GND? 

Kind regards,
Nick Z

Hi Nick,

Nick Zahabizadeh said:

Are TXN or TXP being shorted to GND? 

Yes, when the TXN or TXP in the transmit is shorted to the ground,  one LED will keep working.  MCU can't control the LED current (decrease or cutdown) this situation. Now they cut down the short current by power down and restart. Customer wants our suggestion on this.

Thanks 

Matthew

Hi Nick,

We know that TXN and TXP are not supposed to be grounded. That is the problem they met in some error condition. Customer wonder to know how to control the short current when it happened. Now the MCU can recognize the error but can't cut down the current, they solve it  by power and restart to avoid heating of LED. Do you have suggestions on it ?

Matthew

Hello Matthew,

When the TXP/TXN pin is shorted to ground, the current control DAC in unable to function properly, so it is expected the customer is unable to control current flow. 

Just looking to make sure I understand the customer's question. Are they looking for a way to cut off power to the AFE when the pins are shorted? Does the short remain while they restart the AFE?

Kind regards,
Nick Z 

Hi Nick,

The short till remain but they can cut down the shorted current flow after restarting. So the LED will not get overheated and damage the skin. Customer try to ask if we have suggestion to control the current instead of restarting the whole device.

Matthew

Hi Matthew, 

I would recommend they check how and why the shorting occurs. The AFE4403 has an internal diagnostics system that can check where the TX and PD pins are being shorted. Please see section "8.4.2 Diagnostics" in the AFE4403 datasheet. 

Kind regards,
Nick Z