CDCLVC1310: Schematic review of the CDCLVC1310

Lacey Lin

Intellectual 2900 points

Part Number: CDCLVC1310

Hi team,

Below is the schematic of the CDCLVC1310.

But customer test the XIN pin and get below wave:

Can you help to comment what's the cause of the issue?

is it because the cap input value or maybe the PCB layout?

Lacey

Thanks a lot!

over 5 years ago

0 Alan O over 5 years ago

TI__Mastermind 32575 points

Is the spike only in the XTAL oscillation only during initial startup (I only see single trigger on the o-scope)? Or, do the spikes happen continuously (or periodically) after startup?

What are the crystal specifications?

Do they have bypass caps (like 0.1 uF) near each VDD and VDDO pin?

Alan

0 Lacey Lin over 5 years ago in reply to Alan O

TI__Intellectual 2900 points

Hi Alan,

Thanks so much for your reply!

Below is my inputs:

1. The spike happened with possibility when the device power on. It doesn't have the specific period.

2. This spike don't affect the output signal

3. The specs of the XTAL is as below:

4. They have add the bypass cap in the VDDO and VDD.

5. they select the mode to be 01 as the XTAL or override mode.

Should the customer change the mode to XTAL bypass mode?

The point to choose the XTAL override mode or bypass mode is just the max voltage of the XTAL output?

If the voltage is larger than 2V, then we need to choose the XTAL bypass mode. right?

Any circuit design difference need to be done between the XTAL bypass mode and the XTAL override mode?

Lacey

Thanks a lot!

0 Shawn Han over 5 years ago in reply to Lacey Lin

TI__Genius 9920 points

Hi Lacey,
The problem is caused by unmatched CL and over drive level on XTAL.
The method is to reduce two external from 27pF to 6pF (notice CDCLVC1310 has on chip CL 12pF, and PCN strays cap is around 2~3 pF ), and change current limit resistor R14221 from 0 Ohm to an initial 1 kOhm.
Tuning R14221 to make sure Vpp on XIN <= 0.24V. Notice the resistor can't be too large, otherwise there is no oscillation.

For CDCLVC1310 setting, there is no difference for XTAL mode and overdrive mode, this overdrive is for a LVCMOS input, means re-driving a strong signal again.

Regards,
Shawn

0 Lacey Lin over 5 years ago in reply to Shawn Han

TI__Intellectual 2900 points

Hi Shawn,
Thanks so much for your reply!
just to confirm, the maximum input Vpp in XIN is 0.24V or 2.4V?
I check the specs in the datasheet, in the override mode, the max swing is 2V.
Can you help to confirm?
Lacey
Thanks a lot!

0 Shawn Han over 5 years ago in reply to Lacey Lin

TI__Genius 9920 points

Hi Lacey,
0.24Vpp is limited by crystal drive level, not CDCLVC1310 spec. Current your measurement is around 2.69V-2.10V= 0.59Vpp, which is too large for the crystal in the current application.

Regards,
Shawn