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THS3001 gets really hot

Sergio Hernandez-Montero
Prodigy 30 points
Other Parts Discussed in Thread: THS3001

Hello to everyone, we are having several problems using THS3001 and we were wondering if we could have some help.

The schematic below ilustrates our circuit, a simple non-inverting amplifier with the next considerations:

- Gain: ~ 80 V/V.

- Minimum required BW: 20 MHz approx.

- Input signal amplitude range: 0-30Vpp.

- Because of application restrictions it is not possible to limitate input voltage nor including any resistor at the input.

The amplifier operates very good while it is not saturated and have a regular temperature of ~ 40ºC. Problems come when the amplifier starts saturating (with ~300 mVpp at the input), at this moment it starts to get very hot (70-80ºC) and finally breaks even with low frequencies (500kHz). Notice that the application requires that it must support up to 30Vpp at the input, although it is saturated most of the time.

We've tried to increase the feedback resistor as much as we can (up to1k) to reduce the output current as much as we can but the problem persists. THS3001 datasheet specifies that the amplifier resists an input of +- Vsupply, then ¿why do we have this problem?¿Any idea or solution?

  • 0
    TI__Genius 13935 points

    Hello Sergio,

    I do not see a maximum input voltage in the EC tables.   Are you using the Absolute Maximum ratings to determine that the input can take 30V? 

    There are two package options for this part.  Which one are you using? The DGN package will dissipate more heat.

    It is hard to debug heat issues without a lot of measurements. Do you have any measurements of the output voltage when the part is overheating?  What is the supply current when the part gets hot?

  • 0 in reply to Loren Siebert 1
    Prodigy 30 points

    Hi Loren,

    Yes, I'm using the Absolute Maximum Ratings to determine that the input voltage can be within +-Vcc.

    At this moment we're using the D8 package without the thermal PAD. The problem with THS3001 thermal pad is that it is recomended to be connected to -Vcc, and our dissipation plane is GND.

    The device does not saturate until the output has a value of 26Vpp, while it is not saturated current consumption is about 6.5mA in the Vcc branch. Once it is saturated, the current consumption increases exponencially as the input increases. I write you here some values:

         Vin                          Icc

    230mVpp                6.5mA

    1Vpp                        12.8mA

    2Vpp                        24.4mA

    I hope that would be enough.

    Greetings and Thanks a lot.

  • 0 in reply to Sergio Hernandez-Montero
    TI__Genius 13935 points

    Hello Sergio,

    I think you are damaging the input transistors. 

    When the amplifier is operating closed loop the inputs (+ and -) are always at the same voltage.  The EC tables say that this voltage range is +-12.9V. 

    You have the amplifier set for a gain of 80V/V and you are seeing a very large current increase for input signals that saturate the device output stage.  When the output is saturated the amplifier is no longer closed loop.  This means that the inputs (+ and -) are no longer guaranteed to be close in voltage. 

    If you look at Figure 47 and page 18 you will see that between the two inputs are a pair of diodes and then the input buffer transistors.  In the schematic you sent to me the resistor between the inverting input and ground is only 2.2 Ohms.  This means that there are only two diode drops (~1.2V) and a 2.2 Ohm resistor between the positive input and ground.  It looks like this current is destroying the input transistor. 

    It is very likely that there are ESD protection diodes that are also helping to protect the inputs, but most likely these consist of a set of 4 diodes with 2 diodes each in series (for a protection voltage of ~1.2V).  These diodes can also be damaged by too much current. 

    This is an issue that will occur with any amplifier operated under these conditions.  You may need to consider finding a voltage clamp.  I will see if I can find anything that I can recommend.

    [Edit]  In the Absolute Maximum section it shows a maximum differential input voltage of +-6V. 

    Loren

  • 0 in reply to Loren Siebert 1
    Prodigy 30 points

    HI Loren,

    You're right. We misunderstood the datasheet info. Thanks a lot for your help.

    Greetings.