TMS320F28035: TEST2 PIN #38 on 80 pin device

Brandon Dyer

Part Number: TMS320F28035
Other Parts Discussed in Thread: TEST2

Hello,

I have a custom board using the F28035 and had a question concerning the TEST2 PIN #38 on the 100 pin device. On my design I had connected the TEST2 pin to ground and did not realize it until I had built my pcb. Is there any problem with the TEST2 pin being connected to ground or should I change the layout so it is NC? Also, do you think it would hurt the MCU if I cut the pin off instead of changing the layout for now? Thank you so much. I appreciate all the feedback you guy provide.

-Brandon

over 8 years ago

0 Gautam Iyer over 8 years ago

Guru 192875 points

Hi Brandon,

Grounding the pin should do no harm. Do refer this post:
e2e.ti.com/.../2165770

Regards,
Gautam

0 Brandon Dyer over 8 years ago in reply to Gautam Iyer

Intellectual 610 points

Gautam,

Thanks for the quick response. Does it matter that I have a direct connection to ground instead of a connection via 10k resistor as in the post you referred me to? Thanks.

-Brandon

0 Gautam Iyer over 8 years ago in reply to Brandon Dyer

Guru 192875 points

Brandon Dyer said:
Does it matter that I have a direct connection to ground instead of a connection via 10k resistor as in the post you referred me to?

10K seems to be important here due to some internal circuitry. Not sure though!

Regards,

Gautam

0 Brandon Dyer over 8 years ago in reply to Gautam Iyer

Intellectual 610 points

Gautam,

I will just go ahead and lift the lead from the pad so it is disconnected and let you know if it fixed my problems, which are as follows:

1. The MCU would sometimes not come back on after reset.
2. The MCU would Flash fine for a while and then would start failing to connect to JTAG, resulting in faulty MCU behavior afterwards.
3. A power cycle would be required to get the MCU to power up and run normal sometimes, but eventually a power cycle would no longer work.

Regards,
Brandon

0 Hareesh Janakiraman over 8 years ago in reply to Brandon Dyer

TI__Guru* 95315 points

Brandon,

The issues you describe do not appear to be connected to the TEST2 pin. In any case, no harm in lifting the pin from the board, which is after all the datasheet recommendation. Please refer to this post as well:

https://e2e.ti.com/support/microcontrollers/c2000/int-c2000/f/175/p/64532/1339331

0 Brandon Dyer over 8 years ago in reply to Hareesh Janakiraman

Intellectual 610 points

Hareesh,
I am not able to access the post via the link you provided. I get a message saying the post has been deleted.

Thanks,
Brandon

0 Hareesh Janakiraman over 8 years ago in reply to Brandon Dyer

TI__Guru* 95315 points

The most important piece of information from that post is below:

"TEST2 is a test pin connected to some internal circuitry that can produce various voltages in certain test modes. These test modes should not occur during normal application runtime though. The pin should remain high impedance during normal application runtime. Something wrong would have to occur inside the device to put it into one of these test modes"

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TMS320F28035: TEST2 PIN #38 on 80 pin device