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BUF634: Replacement of the BUF634 with the new BUF634A .

Part Number: BUF634

Hello Team , 

Can you please help me understand what are the key care about which i need to look into while replacing BUF634 with the newer BUF634A ?

  • Hi Schreenidhi,

    It is lower Iq, so you might see a tiny amount more THD+N, but all the fundamentals are actually very similar.

    Best regards,


  • Well I thought I had replied on this, but it did not show up - may later, anyway - the BUF634A is likely a process upgrade on the older version, little faster, what does that 90kHz mean on that front page plot?? 

    Also, these composite circuits always risk low phase margin (section 9.2 talks about that but not conclusively), simply running that sim shows 6dB of peaking that maps to 29deg phase margin (figure 2, in this article). Also, I have to assume this is high current (fast mode) but the model does not include that connection?

  • First starters the BUF643A is a pin-to-pin upgrade for the SOIC package with exact equivalent functionally to the BUF634. So you will not lose any functionality in your application of the original BUF634 with replacing it with the newer BUF634A.

    If your key-care abouts are high slew rate, high bandwidth and low quiescent current then switching to the newer BUF634A would give you all 3 benefits. 

    In fact, 3 reasons you should replace the older BUF634 with the newer BUF634A is we were able to increase the slew rate (2000V/µs --> 3750 V/µs), max selectable bandwidth (180 MHz -->210 MHz) and decreasing the power consumption (15 mA--> 8.5 mA) of the BUF634A when compared to the BUF634.

    Using a buffer in general as a front end of your precision amp helps you increase the output current drive and the low Zout of BUF634 will help you drive much higher capacitive loads without running into stability problems. Decoupling the higher thermal IC with the precision part enables achieving higher accuracy as the precision amp now doesn’t drift.

    Using it standalone is also a very general use case seen across customers where they want to increase the drive strength from an output of a DAC or an amp.

    For additional information check out the applications section of the datasheet Figure 38 & Figure 44.  If you don’t see your application here, I would be happy to showcase the performance difference in your application.

  • Michael,

    90-kHz is the measurement bandwidth that the Audio Precision was configured for when I took the measurement. I always include the measurement bandwidth on THD+N plots because it tells the reader:

    1. How much noise is integrated into the measurement

    2. How many harmonics are included in the measurement

    Quite often I will see THD+N plots taken in a 22-kHz measurement bandwidth. This is fine if the fundamental is 1 kHz. But when sweeping to frequencies above ~5kHz, this measurement bandwidth is obviously too narrow. The harmonics of the fundamental now fall outside the measurement bandwidth. 

  • Thanks John, 

    Of course, the THD+N thing should have been a AP clue. That makes sense for a buffer as you cannot use the more sophisticated approaches developed for op amp type products. Don't see AP generated plots that much in high speed parts where spot noise and HD2 +HD3 sweeps are more common. So the front page is showing a THD +N for for a >200Mhz buffer through 20kHz - an audio pitch apparently.