Problems with the TVP5158 crystal oscillator

Pablo Cassani

Other Parts Discussed in Thread: TVP5158

Hi!,

I've got a system using a TVP5158. On one board over three (and I think I've seen a second, but I cannot repeat it), the crystal oscillator (27 Mhz, 18 pf , using 27pF capacitors to a 0R to GND and XTAL-REF) is not starting when the TVP5158 has over 40 C of temp. If it started and it becomes hot, it doesn't stop working.

Things I've tried:

- Changing crystal. Nothing changes.

- Retouch solders on pins. Nothing changes.

- 1Mohm in parallel with the crystal. Nothing changes.

- 100 ohm in series with Xtal-out. Nothing changes.

- A 27 Mhz oscillator to Xtal-in. It works even when is hot! But still not oscillating with the crystal only.

- Flexing the board. Nothing changes.

- Rapid changes in temp. Works if cold, doesn't if hot.

Any ideas?

Thanks in advance!!!

over 10 years ago

0 Steve Clynes over 10 years ago

TI__Mastermind 43875 points

Crystals not oscillating is most often caused by incorrect load capacitors. Make sure that the load capacitors are matched to the crystal, PCB trace and TVP requirements.

I have also seen some brands of crystal cause issues in certain systems (completely different system, not TVP but mentioning just as an example)

When you heat the system are you also heating the crystal? Try keeping the crystal cool and everything else hot and also try the opposite. As I say, I have seen some crystals stop working when hot, although it is still most likely load capacitor related.

BR,

Steve

0 Pablo Cassani over 9 years ago in reply to Steve Clynes

Prodigy 40 points

The problem was solved. It was related to the JTAG reset, which in our case was connected to a pull-up to a JTAG chain (we have other chips in the JTAG chain).

Disconnecting the TVP from the JTAG chain, and leaving the JTAG pins disconnected solved the problem.

0 Steve Clynes over 9 years ago in reply to Pablo Cassani

TI__Mastermind 43875 points

Pablo,

Thanks for updating the forum. This will certainly help others in the future.

Glad you managed to resolve the issue.

BR,

Steve

0 Eason Wang over 9 years ago in reply to Pablo Cassani

TI__Genius 13460 points

Hi Pablo,

Did you ever draw a conclusion for this case why the JTAG pull-up resisters will affect the crytal oscillate?

Recently I also have such case and this works for me.

Thanks & Best Regards,

Eason

0 Steve Clynes over 9 years ago in reply to Eason Wang

TI__Mastermind 43875 points

The datasheet clearly states to leave these floating.

Incorrect pull up/down will put the chip in a test mode.

BR,
Steve

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Problems with the TVP5158 crystal oscillator