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ADL5513 CLPF VOUT filtering

Hi all,

Our customer start to optimize and evaluate the ADL5513 .

In the datasheet, connecting a ground-referenced capacitor (CFLT) to the CLPF pin recommended.

About design for the CLPF pin and VOUT pin filter @ ADL5513,
1.Is the RC filter connecting to CLPF pin available ?
If available, which is Recommended, RC paralel or RC series ?
Is there recommended (limmited) value range of R,C ?

2.RC filter connecting to VOUT pin ,
Recommended (limmited) value range R,C ?
Note is following only?
"The ADL5513 output can drive over 1 nF of capacitance.
When driving such high output capacitive loads, it is required to capacitively load the CLPF pin.
The capacitance on the CLPF pin should be at least 1/50th that of the capacitance on the VOUT pin."

Best regards,

sss

  • Hello sss,

    1. When CLPF pin opens or no external capacitor connecting to its, the Vout output has about 10MHz video bandwidth. The CLPF pin’s capacitor is depending on your input signal. If you connect a capacitor from this CLPF pin to ground, you will reduce the Vout output video bandwidth and improve the output ripples (feedthrough from the input signal, if any). Figure 27 shows the lowpass filtering capacitor connection, CFLT and the formula on page 14 for calculating the capacitor value.
    2. If you must add a capacitor from the Vout pin to ground, this capacitor will further improve the ripples that feedthrough from input signal. This capacitor (at Vout pin) must be 1/50 greater than the capacitor at CLP pin.

    Hope these can help.

    John_C

  • Hi, John_C - san,

    Thank you for quick reply!

    CLPF pin with RC filter is not recommend ?

    Does that cause any problems?

    Best regards,

    sss

  • Greetings sss@jpn,

    John_C is out of the office now. Perhaps I could answer your question:

    A series-RC filter is generally NOT recommended on the CLPF pin, because of the added complication. A simple 1st order capacitor filter is recommended, as shown in Figure 27.

    If customer does choose to use series-RC, there will be extra design effort necessary, to optimize the detector response and output ripple. Output settling characteristics may be somewhat different from that shown in datasheet. Overall performance may not be as good as the simple single capacitor solution shown in Figure 27. Aside from these things, there should be no problems.