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LM61460-Q1: EN/SYNC pin design

Part Number: LM61460-Q1

Tool/software:

Hi Sir

My customer wants to use FPWM mode instead of PFM

1. For the selection requirements of Csync, Rent and Renb, in addition to the following description in the datasheet, are there any other selection requirements for capacitor Csync?

Dataaheet:

It is recommended to keep the parallel combination value of RENT and RENB in the 100-kΩ range. RENT is required for synchronization, but RENB can be left unmounted.

A 3.3-V or higher amplitude pulse signal coupled through a 1-nF capacitor, CSYNC, is suggested.

2. Regarding the power-on and power-off timing requirements, the datasheet only states that the clock signal comes after the EN enable when powering on. Do I need to disconnect the clock signal before turning off the enable when powering off? What are the consequences of turning off the enable directly?

Datasheet: The external clock must be off before start-up to allow proper start-up sequencing.

Thanks,

Yoga Zhang

  • Hi Yoga,

    1. Use 1nF  Csync as recommend by datasheet. Depending on application you don't need RENB if you're syncing from an external clock. RENT range should be around 100kOhms

    2. You have to provide Vin first then EN from external clock only at turn on

    Regards,

    Rahil

  • Hi Rahil,

    Thanks for your reply

    1.Is there anything else to look out for with 1nF capacitors, such as low ESR.

    2.Do I need to disconnect the clock signal before turning off the enable when powering off? What are the consequences of turning off the enable directly?

    I didn't find any description in the datasheet.

    Thanks,

    Yoga Zhang

  • Hi Yoga,

    1. You can use a ceramic cap. They have low ESR compared to electrolytic. 

    2. You can either turn off Vin or enable first. Either one should be fine. 

    Regards,

    Rahil