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LMH1983: About PLL1

Yasushi Fujiwara
Genius 11695 points
Part Number: LMH1983

Hello Experts,

My customer has question as follows. Customer would like to use a following VCXO.
- VCXO(27MHz): EPSON/VG2520CAN_CJGNBB_27MHz
https://www5.epsondevice.com/en/products/vcxo/vg2520can.html

[question]
1. This VCXO can fit for LMH1983?
2. If it can fit for LMH1983, would you please tell a loop filter values?
3. Regarding charge pump current, is it set by device itself automatically? The datasheet stated a below. (datasheet p13, 8.3.2 PLL1 Loop Response Design Equations)
Under normal operation, several of these parameters are set by the device automatically, for example the charge pump current and the value of 'FB_DIV'. When the input reference format changes, both N and the charge pump current are updated, N is changed to allow for lock to the new reference, and the charge pump current is adjusted to maintain constant loop bandwidth.

Best Regards,
Fujiwara

  • 0
    TI__Genius 16845 points

    Hi Fujiwara,

    A1. The VCXO is OK. For CMOS output, directly connect clock signal to XOin+ and bias XOin- to mid-supply with 0.1µF bypass capacitor.

    A2. You can design the loop filter to match the EVM as a starting point (see pages 12, 16)

    A3. Yes, charge pump current is set automatically based on the input type detected.

    Kind regards,
    Lane