TM4C1294KCPDT: RBias short to ground

Munan Xu

Expert 4155 points

Part Number: TM4C1294KCPDT

Hello,

Would connecting RBias directly to ground be an issue if the Ethernet PHY is not used?

Munan

over 1 year ago

0 Ralph Jacobi over 1 year ago

TI__Guru*** 128105 points

Hello Munan,

Yes that would be an issue. It must have the proper RBIAS resistor populated due to Errata Item ETH#03.

https://www.ti.com/lit/pdf/spmz850

Best Regards,

Ralph Jacobi

0 Munan Xu over 1 year ago in reply to Ralph Jacobi

TI__Expert 4155 points

Hey Ralph,

Gotcha, customer did test with a shorted RBIAS pin and it seemed to boot successfully is the requirement be that you're within a certain voltage range? Or is it just that it needs to be pulled down? Would there be a risk of damage with operating in this manner? Is there a max load current for this pin?

Munan

+1 Ralph Jacobi over 1 year ago in reply to Munan Xu

TI__Guru*** 128105 points

Hello Munan,

If the Ethernet PHY is ever triggered to be configured and the resistor is not present, the device will stop functioning.

The common situation for this is with the ROM boot loader. When the device is powered up if Flash is empty then the ROM boot loader will run and configure the Ethernet PHY which will prevent further code execution.

If a 25MHz crystal is used, this can also cause JTAG to be inaccessible.

In the event a customer never intends to enter the ROM boot loader or use the Ethernet PHY, they could get around this, but we really don't recommend the omission.

Best Regards,

Ralph Jacobi

0 Munan Xu over 1 year ago in reply to Ralph Jacobi

TI__Expert 4155 points

Hey Ralph,

Ok appreciate the feedback.

Munan

Arm-based microcontrollers

Arm-based microcontrollers forum

TM4C1294KCPDT: RBias short to ground