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THS3001 PowerPad

Fabian Pfaeffli1
Prodigy 180 points

Other Parts Discussed in Thread: THS3001, THS3091

Hi

In the datasheet of the THS3001 it is said, that by connecting the PowerPad to GND when operating on split supply rails, the distortion gets worse than specified in the datasheet. Well, how much worse will it be?

Generally, i don't get it why you would want to connect a thermal pad to a supply rail rather than GND which in 99.99% of all cases has a MUCH larger thermal mass! Maybe someone can shed light on this :-)

Regards,

Fabian

  • 0
    Prodigy 180 points

    Come on, no one's got a clue about this?

  • 0 in reply to Fabian Pfaeffli1
    TI__Expert 3030 points

    Fabian,

    The THS3001, along with many other (but not all) THS amplifiers, utilize a SOI process where the active circuitry is electrically isolated from the support wafer (bottom of die) by a buried oxide (SiO2) layer (called BOX). In assembly, the die is attached to the thermal pad with low thermal impedance conductive epoxy, which makes an ohmic connection to the support wafer, but not to the active circuitry. There is no electrical connection to any voltage or to the active circuitry of the device. Thus in theory all BiCom devices can connect the power pad to any voltage as long as it does not break down the BOX; to be safe, we specify the power supply rails as the limits.

    The THS3001 is the only BiCom device that shows measurable variation in performance with the power pad connected to different voltages within the power supply range, and performs the best with it tied to the negative supply. In general we recommend to attach to the ground plane for best thermal performance because the ground plane is usually the largest most contiguous metal plane on most board. The concern is thermal performance, not electrical performance; except for the THS3001 as noted above.

    As for the root cause, we are not clear as this issue is not present on any other amplifier built on the same process. As such, we are relying upon empirical measurements for this statement on the THS3001 only.

    Cheers,

    Randy

  • 0 in reply to Randy S
    Prodigy 180 points

    Hi Randy

    Thanks for the clarification. Right now my circuit uses a THS3091 whose PowerPad is connected to GND. In my search for a faster amp I found the THS3001 and was wondering why an obviously similar device cannot be connected the same way like the THS3091, so that led to the questions above :-)

    Best Regards,

    Fabian