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UCC28950: What is the SYNC pin input frequency range for Slave configuration

Santhosh Kumar S
Prodigy 200 points
Part Number: UCC28950

Hi Everyone,

I'm using UCC28950 IC in my design as a slave configuration. I have connected RT pin to GND via 22.6k Resistor. My questions are as follows.

1. Is the Internal Oscillator frequency FOSC same as the SYNC input frequency?

2. Is switching frequency FSW half of the Internal Oscillator frequency?

3. What if I connect RT pin to GND via22.6k Resistor and Give Input clock of 125kHz freq at SYNC pin? what will be the Switching freq, OSC freq and also the frequency of the output pulses?

4. If I connect RT pin to GND via 47k Resistor, will my Oscillator frequency be 126kHz?

5. What will be the frequency of the output pulses OUTA, OUTB, OUTC and OUTD? Is it equal to Switching frequency or Oscillator frequency?

Regards,

Santhosh

  • 0
    TI__Guru* 85616 points

    Hello,

    This is under review and I will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    Please see my replies below.

    1. Is the Internal Oscillator frequency FOSC same as the SYNC input frequency?

    >Sync frequency needs to be faster than the oscillator frequency.

    2. Is switching frequency FSW half of the Internal Oscillator frequency?

    >The effective switching frequency is twice the oscillator frequency.

    3. What if I connect RT pin to GND via22.6k Resistor and Give Input clock of 125kHz freq at SYNC pin? what will be the Switching freq, OSC freq and also the frequency of the output pulses?

    > I would set the sync frequency to 1.1 to 1.2 times the oscillator frequency.

    4. If I connect RT pin to GND via 47k Resistor, will my Oscillator frequency be 126kHz?

    5. What will be the frequency of the output pulses OUTA, OUTB, OUTC and OUTD? Is it equal to Switching frequency or Oscillator frequency?

    >I believe it is the same.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 200 points

    1. Is the Internal Oscillator frequency FOSC same as the SYNC input frequency?

    >Sync frequency needs to be faster than the oscillator frequency.

    Santhosh> When you say faster, how much it should be? If I feed 100kHz pulses at the input of the SYNC pin, what will be the internal Oscillator frequency FOSC of the converter? 

    2. Is switching frequency FSW half of the Internal Oscillator frequency?

    >The effective switching frequency is twice the oscillator frequency.

    Santhosh> In datasheet it is shown as the switching frequency FSW is half of the Internal Oscillator frequency. please see an image below and clarify.

    3. What if I connect RT pin to GND via22.6k Resistor and Give Input clock of 125kHz freq at SYNC pin? what will be the Switching freq, OSC freq and also the frequency of the output pulses?

    > I would set the sync frequency to 1.1 to 1.2 times the oscillator frequency.

    Santhosh> how will you know the oscillator frequency to set the sync frequency? Also, there are 4 frequencies I can see in the datasheet. Sync input frequency, Internal Oscillator frequency, Switching frequency and Converter output frequency. Can you please tell me the relationship between all of these frequencies.

    4. If I connect RT pin to GND via 47k Resistor, will my Oscillator frequency be 126kHz?

    Santhosh> The image you attached shows the relation between RT and Switching frequency not the oscillator frequency.

    5. What will be the frequency of the output pulses OUTA, OUTB, OUTC and OUTD? Is it equal to Switching frequency or Oscillator frequency?

    >I believe it is the same.

    Santhosh> Can you please elaborate your answer. you mean frequency of the output pulses is same as the switching frequency and also oscillator frequency?

  • 0 in reply to Santhosh Kumar S
    Prodigy 200 points

    Mike,

    Please help me clarifying the above mentioned points.

  • 0 in reply to Santhosh Kumar S
    TI__Guru* 85616 points

    Hello,

    Your inquiry has been received and is under review.

    Regards, 

  • 0 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    Please see my comments below.

    1. Is the Internal Oscillator frequency FOSC same as the SYNC input frequency?

    >Sync frequency needs to be faster than the oscillator frequency.

    Santhosh> When you say faster, how much it should be?

    >1.1 to 1.2 is a good taret.

    If I feed 100kHz pulses at the input of the SYNC pin, what will be the internal Oscillator frequency FOSC of the converter? 

    110 kHz to 120 kHz

    2. Is switching frequency FSW half of the Internal Oscillator frequency?

    >The effective switching frequency is twice the oscillator frequency.

    Santhosh> In datasheet it is shown as the switching frequency FSW is half of the Internal Oscillator frequency. please see an image below and clarify.

    >So the clock is running at 2 X the frequency of each output.  You seem to be correct on this according to the data sheet.

    3. What if I connect RT pin to GND via22.6k Resistor and Give Input clock of 125kHz freq at SYNC pin? what will be the Switching freq, OSC freq and also the frequency of the output pulses?

    Santhosh> how will you know the oscillator frequency to set the sync frequency? Also, there are 4 frequencies I can see in the datasheet. Sync input frequency, Internal Oscillator frequency, Switching frequency and Converter output frequency. Can you please tell me the relationship between all of these frequencies.

    >If the output frequency is 125 kHz the oscillator frequency it set to 250 kHz.  If the sync is in leader operation the frequency on the sync pin should be 250 kHz.

    4. If I connect RT pin to GND via 47k Resistor, will my Oscillator frequency be 126kHz?

    Santhosh> The image you attached shows the relation between RT and Switching frequency not the oscillator frequency.

    >I read the data sheet and you are correct.  The internal oscillator is 2 X.

    5. What will be the frequency of the output pulses OUTA, OUTB, OUTC and OUTD? Is it equal to Switching frequency or Oscillator frequency?

    >I believe it is the same.

    Santhosh> Can you please elaborate your answer. you mean frequency of the output pulses is same as the switching frequency and also oscillator frequency?

    >After reviewing the data sheet the switching frequency is for one output which is half the internal oscillators.  I found these figures in the data sheet for a visual representation.