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LM98725: CMOS Output Format

Part Number: LM98725

Hi team,

A question from one of our customers:

The LM98725 is 8bit*2 in CMOS output format, the customer docks a chip that is an 8-bit DVP interface, but the software does not allow sampling eight bits MSB and eight bits LSB on the positive and negative edges of the LM98725 CLKOUT. Sampling can only be performed for a single-edge transition, that is, only a rising edge or a falling edge sample can be sampled.

I would like to confirm that the INCLK and CLKOUT of the LM98725 are the same frequency and phase signals? If so, can the customer output a clock with frequency 2*INCLK and a clock with frequency INCLK as CLKOUT and INCLK for LM98725 respectively, from the CPU? That is, only the rising edge of the 2*CLKOUT signal is sampled. This is shown in the following figure 

Best Regards,

Amy Luo

  • Hello Amy Luo,

    Thank you for your interest in the LM98725. I will forward the question to the appropriate expert. Please expect a response by July 18th.

  • Hello Amy,

    I reached out internally to about your inquiry. It seems that CLKOUT is the same frequency as INCLK, but unsure about their phase signals (there could be delays within the internal circuitry). 

    Regarding your work around, its a bit difficult to say as the part does not have a lot of documentation about the device and the relationship between CLKOUT and INCLK (in regards to the phase signals). Can you provide additional details on how the customer is utilizing the device with the workaround?

    • A schematic with connections would be helpful to better understand the customer's application.

    Best regards,

    Bill Chieng

  • Hi Bill,

    Schematic: CCD.pdf

    Can a double frequency circuit be terminated at the CLKOUT output of LM98725 to resolve the above issue? 

    If yes, can you help recommend a double frequency circuit  or IC?

    Thanks,

    Amy

  • Hello Amy,

    Thanks for the schematic. I will look into your follow up question. Please expect a response by July 22nd.

    Best regards,

    Bill Chieng

  • Hello Amy,

    A follow up, the Doubled CLKOUT method may work, but the customer needs to verify this method with their own system. Regarding this application, we never recommended a frequency multiplier before for this particular application. Therefore, we do not have a recommended IC or discrete config. to perform the doubled CLKOUT.

    Best regards,

    Bill Chieng