Advertisement

Blog

Zap! High Voltage Op-Amps Are Here

I see that Linear Technology (LTI) has introduced a new op-amp that they are calling a 140 V device.

The specs look pretty darned good — single supply operation of 140 V supply or ±70 V where you need bipolar operation. Rail-to-rail output, so you can take full advantage of the available high-voltage supplies. Input leakage/bias current is as good as many low-voltage devices — typically 3 pA. The input offset voltage is nothing special at a maximum of 1.6 mV, but tolerable considering the device. Gain bandwidth product (GBW) is 10 MHz and slew rate is 19 V/µs. Low frequency noise is spec'd at 3.5 µV p-p; so pretty good for the likely applications.

Those applications are typically as a pin driver in automated test equipment (ATE), as a piezo-driver, or possibly to buffer and amplify the output from a DAC. Piezo devices are often used as actuators and occasionally as transformers. Audio applications are a possibility too.

Conceivably, this op-amp could be used in a servo-amplifier. Combined with suitable power FETs, you'd have a dandy high-power amplifier. I did a design like that to drive a 90 VDC motor a few years back. I had to jump through hoops to come up with a design. I had to level shift and amplify the output of a conventional ±15 V op-amp up and down suitably to drive the output stage (and it had to remain stable — a desirable feature). This portion of my design used a handful of bipolar NPN and PNP transistors.

Of course, if I did that same design now, I'd probably use an H-bridge topology and a PWM drive. But that would be specific to a motor drive. The pin driver and piezo-actuator applications will likely remain purely analog in the foreseeable future. Further, they are not high-power applications, so they are a good match for this op-amp.

The LTC6090 is available in the standard SO-8 package and in a TSSOP package; the TSSOP package includes guard pins adjacent to the input, output, and supply pins. Why do you care about guard pins? If you are sending low-level signals to the op-amps high input impedance inputs — and considering that right nearby there will be some very high voltage — you will surely care about this feature.

And just one more detail about the packages. They have a copper slug that can be soldered to a copper plane on the PC board to help pull heat out of the package.

That's the copper slug on the underside of the package shown by the dashed vaguely rectangular polygon.

That's the copper slug on the underside of the package shown by the dashed vaguely rectangular polygon.

With a ±70 V supply and a possible maximum output current of 10 mA, power dissipation must be considered. The quiescent current for the device is just under 4 mA. Small quantity pricing is around $3.50.

You can find the datasheet at Datasheets.com, and more detailed info right from Linear Technology by clicking here.

7 comments on “Zap! High Voltage Op-Amps Are Here

  1. jkvasan
    February 8, 2013

    These HV opamps would be very useful. Another device from Linear Technology would be LTC4151 – High Voltage I2C voltage and current monitor. Works in a range of 7V to 80V. Has split I2C data pins to drive opto isolators – this feature is very handy. Could be very useful in power circuits.

  2. Michael Dunn
    February 9, 2013

    It always surprises me how small power devices have become, relying on PCB planes to draw away the heat. I remember the good old days, when high-I/V op-amps came in big, multi-pin TO-3 types of cases. Yeah.

  3. Brad Albing
    February 9, 2013

    I recall those too – I think Apex made most of 'em.

  4. Michael Dunn
    February 9, 2013

    They were definitely a main source. Didn't National acquire them? Oh, no, I'm thinking of Comlinear, who may have had similar. I find these acquisitions amusing. Comlinear is now TI, twice-removed…

  5. eafpres
    February 10, 2013

    Regarding heat removal, there are some interesting solutions that weren't there in the old days (depending on how old you are…).  Today, there are thermally enhanced PCB substrates that are combined with a metal layer to transfer heat through the dielectric to the metal layer which acts as a heat spreader.  In addition, a few companies have developed insulating thermal pads which are thermally conductive but electrically insulating; these can be used under the package to enhance heat transfer to the board without risking shorting to power.  

    Bergquist, Laird Technologies, Dow Corning, and Chomerics among others make some interesting materials for these applications.  Anyone used enhanced thermal solutions in their high-power designs?

  6. analog_man
    February 11, 2013

    Apex was acquired by Cirrus Logic but recently spun back out as a private company. TO-3's are still a viable solution if you want to deliver 10 or 20A (as opposed to 10mA from this nice little LT device)

  7. Brad Albing
    March 28, 2013

    And at the same time we're doing these clever tricks w/ the PC boards to pull away the heat, there are water cooled heatsinks available for the very fast uP.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.