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TLV9064: TLV9064 to drive 13ohm load

Nic Lin
Intellectual 2020 points
Part Number: TLV9064
Other Parts Discussed in Thread: LMV301, TLV320AIC3254

Team, can TLV9064 be used to drive 13ohm load and get 200mVrms output? Looks like the output current in datasheet can meet this. 

Regards,

Nic

  • 0 in reply to kai klaas69
    TI__Intellectual 2020 points
    I am asking this because I am thinking to use TLV9064 as the oscillator output buffer .
  • 0 in reply to Nic Lin
    Guru 140200 points
    Hi Nic,

    no, the TLV9064 is not capable of driving a 13R load. No standard OPAmp can do this. But you can add a transitor stage, like it can be seen with headphone amplifiers. Or you can take a special headphone amplifier chip or a Power OPAmp.

    Kai
  • 0 in reply to kai klaas69
    TI__Intellectual 2020 points

    Note it. I am familar with headphone amplifier. Do you have any Power OPAmp part number come to mind?

  • Former Member
    0 Former Member in reply to kai klaas69

    TLV9064_13Ohm_Load.TSC

    Hi Kai,

    Which limitation of the op amp makes you think it cannot drive the 13 Ohm load?

    From the TLV9064 datasheet's figures 10 and 30 (claw curves and full-power bandwidth), I would think neither output current nor frequency of operation will be of concern.  I've simulated the circuit (see attached) and the part does not seem to encounter any limits.

    I've assumed a 300mVpp output wave for margin, centered around 0V, +2.5V and -2.5V supplies, and a 30kHz frequency.

    Daniel

  • 0 in reply to Former Member
    Guru 140200 points
    Hi Daniel,

    300mV across 13R means a load current of 23mA. The specified typical short circuit current of TLV9064 is +/50mA. Unfortunately, the short circuit current decreases with increasing temperature, according to figure 29 of datasheet. But more important is that the short circuit current can show huge manufacturing tolerances. Unfortunately, the datasheet does not specify any manufacturing tolerance of short circuit current.

    To get an idea of how much the short circuit current might differ from chip to chip, a look into the datasheet of LMV301 can be helpful. While the specified typical short circuit current is 60mA at 25°C, the specified minimum short circuit current is only 10mA at 25°C! So, for my taste the output current of 23mA is not far away enough from the +/-50mA short circuit current specification of TLV9064. And even if the short circuit current limiting might not be fully activated, a partially activated short circuit current limiting can result in considerably increased distortion.

    Another issue is the open loop gain. CMOS OPAmps are known for the fact that the open loop gain can heavily decrease when decreasing the output load resistance. As the TLV9064 appears to be optimized for loads >2k and many figures are shown with a load resistance of 10k, for my taste a load resistance of 13R seems all too low. A decreased open loop gain can also result in increased distortion.

    Kai
  • 0
    TI__Guru*** 139836 points
    Nic,

    Can you add an 'impedance matching' transformer?
  • 0 in reply to Ron Michallick
    TI__Intellectual 2020 points
    This is going to be used in headphone application. Transformer is way too big...
  • 0 in reply to kai klaas69
    TI__Intellectual 2020 points
    Hi Kai, except headphone amp, any other OPAmp option?
  • 0 in reply to kai klaas69
    TI__Intellectual 2020 points
    HI Kai,

    If customer decrease the output current requirment to 10mA, can TLV9064 be used in this case? Or there is still some risks? We tend to use it as a follower to drive 13ohm load. The small package of this device impresses customer.

    Nic
  • 0 in reply to Nic Lin
    TI__Intellectual 2020 points

    Customer just changed spec to have 60kHz output. Now we are thinking to have below scheme.

    TLV320AIC3254 is used to generate sine wave. TLV9064 is used as a follower to drive 13ohm load. Maximal output current is 10mA. 4CHs are needed. 

    Do you think if it works?

  • Former Member
    0 Former Member in reply to Nic Lin
    Hi Nic,

    I have consulted with some of my colleagues. They have shared the following.

    1. They do not expect the variation in short circuit output current to be significant enough to be an issue for the design.

    2. Because your load resistance is so low, the gain bandwidth product (GBW) of your part will be degraded. With an open loop output impedance of about 100 Ohms for the part and a load of 13 Ohms, we can expect to have a reduced GBW of GBW*13/(13+100). Since the GBW is typically 10 MHz, your new GBW will be 1.15 MHz. Given the buffer configuration and the 60kHz input signal, this should not be an issue but it is something to be aware of.

    3. The primary concern will be power dissipation. You can get a rough estimate of the dissipated power by taking 1/2 the supply voltage and multiplying by the output current, assuming the supply voltage is much greater than the output swing and the output is centered at 1/2 the supply voltage. You can use a package with a thermal pad to help with this issue.

    If you have a value for the output capacitor, we can simulate the circuit. Let me know if you have any more questions.

    Regards,
    Daniel
  • 0 in reply to Former Member
    Guru 140200 points
    Hi Daniel,

    thank you for clearing the short circuit current and open loop gain issues!

    Kai
  • Former Member
    0 Former Member in reply to kai klaas69
    Hi Kai,

    Thanks for your support and constructive feedback as always! It is much appreciated.

    Regards,
    Daniel
  • 0
    TI__Intellectual 2020 points
    Team, we plan to evaluate TLV9062S for this application. Do we have avaiable EVM to evaluate VSSOP or X2QFN package?
  • 0 in reply to Nic Lin
    TI__Genius 15410 points

    Hi Nic,

    I recommend using the SMALL-AMP-DIP-EVM to evaluate the TLV9062S in the X2QFN (RUG-10) package. I'm not aware of an EVM that can accommodate the VSSOP-10 package.

    Thank you,

    Tim Claycomb 

  • 0 in reply to Tim Claycomb
    TI__Intellectual 2020 points

    Thanks Tim. But I could not find the part number of TLV9062S X2QFN package in datasheet. Could you let me konw what it is?

  • 0 in reply to Nic Lin
    TI__Genius 15410 points

    Hi Nic,

    The TLV9062S in the X2QFN package has not been released online yet. I will contact you directly via email to provide samples and RTM dates for the TLV9062S X2QFN (RUG-10).

    Thank you,

    Tim Claycomb