TPIC8101: Xtal &

user5163865

Part Number: TPIC8101

Tool/software:

Hi,

Our customer created a prototype using the following constants and Xtal, and some samples had problems starting up the oscillator when the power was turned on.

Q1
The customer said they performed matching, but what is the problem?
Please let me know if there is an acceptable range for the recommended constants.

Q2
The specifications for Xtal are as follows. The load capacitance is 8pF. Is this OK?

Xtal :NX3225GD-8MHz

c_NX3225GD_STD_CRA_3_e-1317534.pdf (mouser.com)

We apologize for the inconvenience, and would appreciate your assistance.

Best regards,
Hiroshi

11 months ago

0 John Miller - Sensing 11 months ago

TI__Mastermind 40295 points

Hiroshi,

Would it be possible to try different value capacitors?
Your schematic shows 2 x 4pF, but PCB pads and traces may add more capacitance via parasitics.
As a start could you try some smaller caps?

Regards,
John

0 user5163865 11 months ago in reply to John Miller - Sensing

Genius 3980 points

John-san,

Thank you for your support.

I asked the customer to improve it with a smaller capacitor. I will report the results when I know them.
I also found the following answer in another thread.

(12) TPIC8101: question about knock sensor - Interface forum - Interface - TI E2E support forums

Historically, I know that this part has been used with 20 Ohm ESR/30pF and 80 Ohm/20pF crystals.
There could be issues if using a much higher ESR crystal.

The ESR of the Xtal that the customer is using is 500Ω, which seems too high.
So, at the customer's request,

Could you please tell me the part number/supplier of Xtal that TI has confirmed to work, and the values of the resistor and capacitor?

I apologize for any inconvenience this may cause. Your support is greatly appreciated.

Best regards,
Hiroshi

0 John Miller - Sensing 11 months ago in reply to user5163865

TI__Mastermind 40295 points

Hiroshi-san,

We have no experience picking out crystals for the TPIC8101.

The best path forward is most likely to check with the crystal suppliers for a part with the parameters called out in the TPIC8101 thread you referenced.

Regards,
John

0 user5163865 10 months ago in reply to John Miller - Sensing

Genius 3980 points

John-san,

We have received additional request from the customer.
They would like to receive an official answer from TI, regarding the following:

Q1.
https://e2e.ti.com/support/interface-group/interface/f/interface-forum/653407/tpic8101-question-about-knock-sensor?tisearch=e2e-sitesearch&keymatch=TPIC8101%2520Xtal

It says 20 Ohm ESR/30pF and 80 Ohm/20pF crystals, but when using crystals, is the ESR upper limit of 80Ω standard of this IC?

Q2.
Datasheet P5

"150-mV input amplitude on the 4-MHz clock input only applies if the feedback network is completed. Without the feedback network ....,"

It is the same for other frequencies (OSCIN frequency 4 to 24MHz), and if there is 1MΩ between Xin and Xout, is 150mVpp sufficient for the feedback resistor?

Q3
Datasheet P10

8.3.1.7 XIN
The external clock signal from the MCU,
"crystal, or ceramic resonator is configured with resistors and capacitors.", but the requirements for the crystal and ceramic resonator are unclear, so we would like you to provide a circuit diagram including the constants.

Thank you for your long-term support.
I apologize for not being able to solve the issue with my knowledge.

Best regards,
Hiroshi

0 user5163865 10 months ago in reply to user5163865

Genius 3980 points

Regarding Q2, I will attach the D/S specs just to be sure.

If there is a 1M ohm feedback resistor, would it be okay to use 150mVpp with an 8MHz crystal?

0 John Miller - Sensing 10 months ago in reply to user5163865

TI__Mastermind 40295 points

Hiroshi-san,

I will investigate the customers questions and provide an update before COB on Monday.

regards,
John

0 user5163865 10 months ago in reply to John Miller - Sensing

Genius 3980 points

John-san,

Thank you for your support.

I apologize for the inconvenience.

Best regards,
Hiroshi

0 John Miller - Sensing 10 months ago in reply to user5163865

TI__Mastermind 40295 points

Hiroshi-san,

With respect to your questions:

We don't have a range of ESRs for the crystal over all operating conditions.
Since the past E2E post references a successful use of the 80Ω crystal, that might serve as an upper limit, but the the customer should be sure to test their design over all operating ranges.
To be honest, the footnote is a little confusing. The footnote text is about the clock, but it is positioned in the section about the analog input amplifiers.
This is probably due to a writer/editing error in the document.
As a guess, I'd say the clock feedback network should apply to all clock frequencies.
There doesn't seem to be any internal guidance or requirements for the crystal/resonator requirements.
The best approach would be to pick the best crystal/resonator that meets their needs, and test the design thoroughly over all operating conditions.

Regards,
John