UCC28070: How to sync with correct PWM pulse

Derek Chan1

Part Number: UCC28070

Hi,

I am testing the UCC28070 EVM and would like to sync by external pulse. How can I do that? Is there any sync pulse requirement (amplitude, duty etc)? When I am using 440kHz to 550kHz with different duty cycle (up to 80%), I still cannot sync the EVM. Please help. Thanks.

over 7 years ago

0 Peter Meaney over 7 years ago

TI__Mastermind 31580 points

Hi Derek

On page 6 of the datasheet you can find the details of the sync pulse, Rising threshold is 1.5V max, min falling threshold is 0.4V, pulse width greater than 200ns, but please read footnote 2 on the page.

Regards

Peter

0 Derek Chan1 over 7 years ago in reply to Peter Meaney

Prodigy 190 points

Hi Peter,

I am using the pulse as shown in channel 2 below 500Hz 5V D=30%. but there is no change of the fsw at ch1. Can you advice if there is anything wrong? Thanks.

0 Derek Chan1 over 7 years ago in reply to Derek Chan1

Prodigy 190 points

It should be 500kHz.

0 Peter Meaney over 7 years ago in reply to Derek Chan1

TI__Mastermind 31580 points

Hi Derek,

The UCC28070 is only designed to switching up to 300kHz so it will not sync to the 500kHz sync signal.

Regards

Peter

0 Peter Meaney over 7 years ago in reply to Peter Meaney

TI__Mastermind 31580 points

Hi Derek,

I should have mentioned that in order to sync to an external clock signal the sync signal should be higher than the free running clock frequency of the UCC28070 but by only 10% to 15%.

Regards

Peter

0 Derek Chan1 over 7 years ago in reply to Peter Meaney

Prodigy 190 points

Hi Peter,

AS mentioned in the datasheet, fpwm = fsync/2 that why I set 500kHz as my desired frequency is 250kHz. I am confused about what you are talking 10% to 15% higher than the clock frequency. Can you explain more the difference between this and yours? Moreover, any amplitude requirement for the injected sync signal. Thanks.

Derek

0 Derek Chan1 over 7 years ago in reply to Peter Meaney

Prodigy 190 points

Peter,

I adjust to lower switching frequency 100kHz (Originally, it is default 200kHz), it can be sync by external pulse. However, when I increase the external frequency to 430kHz, the EVM cannot be further sync by this freq. Can you advice why it is happen? Is there any limitation of the switching frequency that affect the sync function? Thanks.

Derek