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LTC5564 Peak Power Input

Hi,

I'm interested in using the LTC5564 but wanted to check with your team if you had a more specific RFIN power rating.

The datasheet has the device rated for 16 dBm (assuming RMS) and a RFIN Voltage (for Vccrf = 5V) of 7 V. Do you have a max RF Pulse width rating at this voltage?

A bit more on my application, I'm expecting to drive this RF Detector with up to 23 dBm in, but only for 800 ns pulse widths at a very low frequency (~300 Hz). Do you have any data/can you provide any insight to the peak power capabilities of this device?

Thanks,

Chris

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  • Hi Chris,

    Is your expected input signal:

    a) a single rectangular 800ns pulse of DC that repeats at 300Hz repetition rate? Or,

    b) a 800ns wide pulsed RF signal at some RF carrier frequency, that repeats at 300Hz repetition rate?

    LTC5564 is designed and characterized for the use case b) above.  It will detect the signal of case a) above, but it is not specified or characterized for that type of usage. The device utilizes internal Schottky diode detector, which is designed to peak-detect a 600MHz to 15GHz RF input carrier frequency.

    The Abs. Max Ratings specs for RFIN Power and RFIN Voltage are for continuous duty. Notice from graph on datasheet page 1, an input of +23dBm for signal of type b) above would be literally 'off the chart' output signal. 

  • Thanks for the reply Bruce! Sorry I should've clarified, we're using an Xband signal so I meant case B at a pulsed input power of 23 dBm, 800ns pulse width, with a rep rate of 300 Hz.

    I'm not sure I understand the RFIN Voltage rating of 7 V. Can the input voltage sit at 7V DC indefinitely?

    Also is there a duty cycle rating of the 16 dBm (4V pk-pk) rating? I understood that as a CW rating but could you pulse the device at a very low duty cycle at a higher power level without failure? I understand the device would clip in its output voltage, I just want to know if it would cause the device to fail immediately.

    Thanks,

    Chris

  • Hello Chris,

    The LTC5564 will do a great job of detecting your X-band signal as specified, but for optimal performance, do take a look at and consider the input matching network. Also the Demo Board manual (a.k.a. User Guide) online has some additional matching network suggestions for your reference when using the factory eval board. If you're putting the device on your own custom PCB, the X-band matching will likely need fine tuning if optimal results are desired. For input impedance matching with this device, we have S-parameter measurements posted online if you're comfortable with such endeavors. 

    If you wish to skip all the RF input matching optimization, you might consider the ADL6010 or ADL6012 Schottky detectors, both of which have broadband matched input, no matching required. 

    Now on to your specific questions:

    1. The max voltage spec at RFin is really not that useful as a spec, because we ALWAYS require AC coupling at that pin. It's a necessity for the device to function properly. The external capacitor enables the device to self-bias. But the direct answer is Yes, that is a continuous duty cycle rating. 

    2. The max RF input power rating does not have a duty cycle element, although that is a FAQ. It's a simple CW rating, and it's conservative. There should be quite a lot of margin built into that spec, but nonetheless we cannot advise to derate this important line item. A far better and recommended solution is to use resistive pi- or t-pad in front of the detector, to attenuate the +23dBm down to approx. +16dBm (7dB pad). Attenuator pad at the input also helps reduce RF standing waves, generally providing flatter frequency response, a desirable fringe benefit. 

    Hope that helps!  -Bruce H. 

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  • Hello Chris,

    The LTC5564 will do a great job of detecting your X-band signal as specified, but for optimal performance, do take a look at and consider the input matching network. Also the Demo Board manual (a.k.a. User Guide) online has some additional matching network suggestions for your reference when using the factory eval board. If you're putting the device on your own custom PCB, the X-band matching will likely need fine tuning if optimal results are desired. For input impedance matching with this device, we have S-parameter measurements posted online if you're comfortable with such endeavors. 

    If you wish to skip all the RF input matching optimization, you might consider the ADL6010 or ADL6012 Schottky detectors, both of which have broadband matched input, no matching required. 

    Now on to your specific questions:

    1. The max voltage spec at RFin is really not that useful as a spec, because we ALWAYS require AC coupling at that pin. It's a necessity for the device to function properly. The external capacitor enables the device to self-bias. But the direct answer is Yes, that is a continuous duty cycle rating. 

    2. The max RF input power rating does not have a duty cycle element, although that is a FAQ. It's a simple CW rating, and it's conservative. There should be quite a lot of margin built into that spec, but nonetheless we cannot advise to derate this important line item. A far better and recommended solution is to use resistive pi- or t-pad in front of the detector, to attenuate the +23dBm down to approx. +16dBm (7dB pad). Attenuator pad at the input also helps reduce RF standing waves, generally providing flatter frequency response, a desirable fringe benefit. 

    Hope that helps!  -Bruce H. 

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