External clock of UCC28251

Hi Takahiro, An AE will respond soon to your question.

Thank you for your help!

We wait for your answer.
I am glad if you can answer quickly.

Best regards,

Takahiro Nishizawa

Dear Mr.Brian


Thank you for your help!

How is the response status?
I wait for your answer.

Best regards,


Takahiro Nishizawa

Hi Brian,

I'm Kai working with Nishizawa-san,

Could you support Nishizawa-san's question?

What we want to know is the operation of UCC28251 while RT is connected to GND for 1s.

In customer system, an external clock outputs low for 1s and then sends specific frequency.

D/S describes Oscillator frequency vs external resistance.

Does this mean if RT pin is connected to GND(Low state) for 1s, the oscillator frequency is clamped to 1.4MHz, and after that, UCC28251 is synchronized to an external clock?

If there are any problem that oscillator frequency is shifted from 1.4MHz to external clock, the file that Nishizawa-san attached is plan to address that frequency shift.

the file shows Oscillator frequency is set by an external resister for 1s and then synchronized to an external clock.

What do you think this is good way to address this frequency shift or if you have any other good way to address this, please let us know.

thanks,

regards,

Kai

The RT pin has a max voltage range of -0.3V to +3.6V
So pulling this pin low will not damage the device. The device has a frequency range of 84kHz to 1.89MHz when used with an external oscillator.
Since the upper limit of this range is so high it is recommended that you use a buffer type of circuit with a resistor connected directly to the RT pin in order to accurately clamp the upper frequency while the external oscillator is grounded.
This will ensure reliable and repeatable startup.

Regards
John Griffin

Thank you for your help!

I have questions about UCC28251.

Question 1.
- Please tell me the time that should be set from IC enables to external synchronization startup.

Question 2.
- How is the IC when External synchronization is not performed normally?
For example, the IC keeps to operate by frequency of external resistor and so on.

Question 3.
- Please tell me the way When we do not use OVP pin.
For example floating or connecting to GND

Best regards,


Takahiro Nishizawa

Thank you for your help.

How is the confirmation situation?
I am waiting for your answer.
I am glad if you can answer early.

Best regards,

Takahiro Nishizawa

Thank you for your help!

I am waiting for your answer.
Please tell me your view.

Best regards

Hi John,

Could you support Nishizawa-san's question?

Actually customer questions are sequence of CLKIN/EN and OVP/OTP pin termination.

Question 1

Are there any sequence between EN event and CLKIN? if no sequence, i will answer no sequence to them.

e.g. CLKIN ⇒ EN, CLKIN=EN, EN⇒CLKIN, CLKIN within xxms after EN assert or somiting like that.

Question 2

How to terminate OVP/OTP pin when they don't use OVP/OTP pin?

voltage threshold of OVP/OTP pin is 0.7V so this pin should be connected to GND i think.

thanks,

Regards,

Kai

Kai,

You can see the relationship between EN and CLK in figure 23 of the datasheet

CLK starts as soon as EN is applied.

If OVP/OTP is not used it should be connected to GND.

Regards

John

Hi John,

Thank you for your time to disscuss this in the call!

I will answer "there is no sequence between  EN and CLKIN from RT" and "If OVP/OTP is not used it should be connected to GND.".

Thanks,

Regards,

Kai

Dear John-san

Thank you for your answer!

Do you know the operation of IC when External synchronization is not performed normally?

Best regards


Takahiro Nishizawa

Hello Nishizawa-san,

Im not sure what you mean by "not performed normally"
Figure 25 in the data sheet shows how the rising edges of OUTA and OUTB are aligned with the falling edges of the synchronizing clock signal.

Regards

John

Our customer is concerned that the IC does not move from EN to External synchronization Due to some trouble.
Is there any possibility that the IC can not move from EN to external synchronization?

Best regards,


Takahiro Nishizawa

You will have to provide more details of the issue.

The schematic, bill of materials, test involved and test results are needed.

Regards

John