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UCC28950 / Jitter on the OUTpins

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: UCC28950
Hello,
 
There are jitter on Out pins of UCC28950 in our customer test board.
Please see the attached file as wave form of the OUT pins.
Could you please kindly let me know this reason and improvement ?
 
-Conditions.
 Vin=390V
 Vout=50V
 Iout=20A
- I have the schematics of our customer.
  If you contact to me directly by e-mail,  I can send it.
 
I already informed calculation tool and Application Note to the customer.
 
Best Regards,
Ryuji Asaka   
  • 0
    TI__Genius 9790 points

    hello, Asaka

    what is the control mode customer select, voltage mode or peak current mode?

    does customer add slope compensation if customer select peak current mode?

    the jitter maybe caused by the transformer turns ratio is not exact between the primary and secondary windings of the power transformer.

  • 0 in reply to Yunsheng Qu
    Guru 20090 points
    Hello Yunsheng san,
     
    Thank you for the reply.
    Customer select peak current mode.
    Rsum resistor is 120kohms.
     
    I will check the specification of the transformer.
     
     
    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Genius 9790 points

    Hello Asaka-san

    You can try to measure the inductance of the two secondary windings of the transfromer. If the inductances between the two windings has big gap, there may have jitter on the output pins.

    The jitter behavior is just peak curren mode control correcting the duty cycle to ensuring the transforme properly resets after every cycle.

    Regards,

    Yunsheng

  • 0 in reply to Yunsheng Qu
    Guru 20090 points
    Hello Yunsheng san,
     
    Thank you for the reply.
    As I checked transformer specification to our customer , there is the jitter when customer disconnected transformer too( operate control circuit only).
    Thus, I think that there is other reason of this jitter.
     
    I infromed changing  the RSUM resistor( reduce from current 120kohms) and CS pins noise to our customer. 
    Are there any possibility for this jitter , please kindly let me know ?
     
    Best Regards,
    Ryuji Asaka