• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 46 subscribers
  • Views 751 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS4522 problem

Giuseppe Landolfi
Prodigy 100 points
Other Parts Discussed in Thread: THS4522, THS4524

6406.THS4522 - PCB schematic.pdf4061.ths4521 TINA.pdf

Hi,

my problem is that  the Tina's simulation working well, while in the real circuitry I have DC voltages that should not be there.

The dc voltages in the nets are:

PD1 = 1.95V, Vin2+ = 797mV, Vin2- = 797mV, Vocm1 = 562mV, Vin1+ = 1.42V, Vin1- = 806mV, Vocm2 = 1.62V, Vs2+ = Vs1+ = 2.58V, CH1P = CH1N = 1.44V, CH2P = 474mV, CH2N = -273mV

I don't understand where is the problem.

Thanks!

Giuseppe

  • 0
    TI__Genius 17905 points

    Hi Guiseppe,

    Is the voltage at VS1- and VS2- (pins 16 and 12) at the expected -2.5V? Also, when you take these DC measurements, how are the inputs terminated (ch1+/-, and ch2+/-)?

  • 0 in reply to Kris F
    Prodigy 100 points

    Hi,

    VS- (pin16) is at -2.4V and VS- (pin12) is at 1.34V and it is open because I read on the datasheet that VS- is tied together on multi-channeldevices.

    When I take the DC measurements the inputs (ch1+/-, and ch2+/-) are terminated open.

    Thanks

    Giuseppe

  • 0 in reply to Giuseppe Landolfi
    TI__Genius 17905 points

    Giuseppe,

    Thanks for the information. The 1.34V at pin 12 is surprising. Do you have multiple boards and do they all exhibit the same behavior (or have you tried replacing the THS4522 chip)?

    I have seen in the lab using the THS4522 that leaving the inputs open would not cause this behavior, but is there any difference if you tie the inputs to ground?

  • 0 in reply to Kris F
    Prodigy 100 points

    Hi Kristoffer,

    I have 4 THS4522 chips in the same board and all chips exhibit the same behavior.

    Could be that the cause is the pin 12 opened?

    If I tie the inputs (ch1+/-, and ch2+/-) to ground the dc voltages in the nets are:

    PD1 = 1.95V        Vin2+ = 1mV        Vin2- = 1mV        Vocm1 = -1.7mV         PD1=0.72V        Vin1+ = 110mV        Vin1- = 112mV        Vocm2 = 1.56V        Vs2+ = Vs1+ = 2.52V       

    CH1P = 0.98       CH1N = 2.41V        CH2P = 10mV        CH2N = -14.7mV        Vs-(pin16) =-2.52        Vs-(pin12)=0.86V

     

  • 0 in reply to Giuseppe Landolfi
    Prodigy 100 points

    Kristoffer,

    now I have connected the pin 12 to the -2.5V net.

    If I tie the inputs (ch1+/-, and ch2+/-) to ground the dc voltages in the nets are:

    PD1=PD2=1.94V       Vin2+=Vin2- = Vin1+ = Vin1- =0.63V           Vocm1 = -1mV          Vocm2 = 10mV        Vs2+ = Vs1+ = 2.52V       

     

     

     

    CH1P = -0.23V       CH1N = 0.25V        CH2P = -0.8mV        CH2N = 0.8mV        Vs-(pin16)=Vs-(pin12) =-2.52      

  • 0 in reply to Giuseppe Landolfi
    TI__Genius 17905 points

    Hi Guiseppe,

    I have spoken with the design team and we reviewed the wiring/packaging documents. We discovered that pins 12 and 16 on the THS4522 are NOT tied together internally as indicated in the datasheet. They ARE tied together internally for the THS4524.

    I deeply apologize for our error and the impact it may have on your project. We will fix this for future material as soon as possible.

    Assuming the Vs- pins are internally connected as in the THS4524, it is still recommended to route all of the the V- supply pins on your PCB, each with its own decoupling capacitor, so that the supply connection is as low impedance as possible, and there is little supply current being drawn across the part between the different amplifiers.

    It appears the device is working properly now with -2.5V applied to pin 12. The output offset for Ch1 is likely due to the very large gain (400V/V or 52dB), which is amplifying the input offset voltage. Input offset voltage will vary from part to part, even between two amplifiers in the same THS4522 chip. I would also like to point out that the distortion performance will not be as good at high gains compared to at low gains (1V/V, 2V/V, 10V/V) due to the reduced loop gain at high gains. Loop gain is the difference between open loop gain and closed loop gain for the THS4522. From feedback theory, loop gain corrects for gain variation and distortion, among other things.

    Please feel free to e-mail me directly at k.flores@ti.com with any other concerns.