What Can You Do With a Programmable Current Source?

I received a press release recently for an IC that is intended for use in implantable nerve stimulation devices. This caught my eye for a couple of different reasons.

The first has to do with the market for which it is intended — medical device manufacturing. In my career, I've worked for two different companies making medical diagnostic equipment. I've also sold ICs to similar companies. It's good work to do, because you end up being directly responsible for improving people's lives (so, good karma).

The second reason this caught my eye is because I've known people — friends and relatives — who could have benefited from such a device, both for pain management and for mobility.

The IC (CSI021 from Cactus Semiconductor) is a quad programmable pulse generator. Each generator is a current source/sink, capable of sourcing 6mA and sinking 1.5mA into as low as a 1.5kΩ load (i.e., you). They accomplish this by boosting the battery voltage to 18V so the circuitry has plenty of compliance voltage for higher impedance loads. The pulses are capacitively coupled to facilitate sourcing and sinking current.

In an actual application, you would use one or more of the stimulator ICs, a microcontroller, a rechargeable battery, power supply circuitry, and suitable RF tank circuits. Connections for recharging and for the data transfer must be done non-galvanically for safety reasons. Both are done via RF links — hence the need for the two tank circuits. These two wireless links allow the IC plus its associated circuitry and PC board to be implanted. Here's a block diagram showing an 8-channel stimulator:

Clearly a simple design that should be easy to construct and evaluate. But more on that in a moment. Here's a closer look at the IC:

What's interesting here is the inner workings are quite straightforward. It contains current sources, analog switches, DACs, some logic to control timing/pulse generation, and an SPI interface. You could build this in your basement lab. But, you'd have trouble squeezing it down to 4mm square. So an obvious advantage of using the IC is that you can then concentrate your engineering time on the V&V (verification and validation) of the systems software, firmware, and hardware.

Anytime you work on a medical device (evaluative, diagnostic, or implantable) you will need to document every step of the process from the product's inception through the design and marketing stages and on to the point of clinical testing and shipping products. This is not the usual commercial product timeline where you dream it up on Monday and start shipping on Friday.

Also worth noting is that the IC could see use outside of medical apps — it is at heart a 4-channel programmable current source/sink. You can probably think of other applications. If you do, please tell us about them.

Have you worked on any projects that you felt especially good about, that gave you that warm, karmic glow? Let us know in the space below.

14 comments on “What Can You Do With a Programmable Current Source?

  1. Michael Dunn
    April 10, 2013

    I like Cactus's logo.

    But they seem like they might be the kind of company that wouldn't be interested in selling parts to you unless you were making a medical device. Just a feeling…

    Or is it in distribution?

  2. Brad Albing
    April 10, 2013

    Haven't taken a close look at their sales organization or distribution – more interested in the device itself. But you raise a good point. Maybe if one of the Cactus folks sees this, they will comment.

  3. Andy@Cactus
    April 10, 2013

    While the CSI021 was designed with Neuro-Stimulator applications in mind, it might be suitable for a wide range of commercial or industrial applications – as Brad pointed out.

    The part is not yet available, but evaluation units will be available in July, and once they are, Cactus will absolutely sell them for any application.

    To see the CSI021 Datasheet, go to

    For more detailed technical information, e-mail me at

  4. Netcrawl
    April 11, 2013

    @Brad thanks for the great article! @Michael, its a company who has a deep expertise on power management and analog circuits, I believe its technical acumen are well targeted toward suporting medical devices makers, its a kind of products the entire medical industry are looking for. 

  5. SunitaT
    April 12, 2013

    @Brad, thanks for the post.

    The implantation of artificial devices within the human body have become common for maintaining and improving health. Artificial devices have already evolved from artificial hips and knees to assistive devices that have built-in electronics.

    These implantable ICs are the great gift to humankind from the semiconductor industry. I wonder how these ICs charge themselves when implanted in the body?

  6. Netcrawl
    April 12, 2013

    What exactly is the advantages of having implantable devices in improving human health? Can it really solve the common problem we encounter in medicine? 

  7. Brad Albing
    April 12, 2013

    It depends on the problem. The common cold? Probably not. Nerve damage that causes the sensation of pain? Probably yes. Motor nerve damage that causes loss of mobility? Probably yes. Repair of some organs – e.g., for insulin production? Probably yes.

    All this goes beyond an implantable current source, but this is the direction we're moving in.

  8. Brad Albing
    April 12, 2013

    You do need to provide an external source with some devices. The one I wrote about uses an external RF field to couple to one of the tank circuits shown. But other companies are looking at energy harvesting from body heat and body movement.

  9. SunitaT
    April 12, 2013

    Artificial cardiac pacemaker is one such implantable device which is used to regulate the heart beat. This device's main purpose is to generate adequate heart beat in the person whose heart is weak.

  10. SunitaT
    April 12, 2013

    But other companies are looking at energy harvesting from body heat and body movement.

    This reminds me of the MATRIX movie in which the same concept was used. If such energy hartvesting ideas become reality then it will be a great help to users who have devices implanted in their body.

  11. amrutah
    April 12, 2013

    Sorry this is off the topic… but interesting things happening in implantable devices…

    SunitaT: You are right, this is one of the device”the pacemaker”, which is highly used implantable device. At Harvard a team has found out  one more way of strengthening/ rebuilding heart muscles, using “carbon nanotubes”.

     The carbon nanotube is one such device which is very small and can store the charge efficiently for long times… Hope we have more implantable devices in near future…


  12. Brad Albing
    April 30, 2013

    Thanks Andy. Perhaps we can get people thinking about the part in new ways. Always nice to expand your market.

  13. Brad Albing
    April 30, 2013

    Um… I suppose, but even tho' it was a movie, and even tho' we are willing to suspend disbelief somewhat, and even tho' the special EFX were pretty cool, it was based on a shaky premise at best regarding using humans purely as an energy source.

  14. CameronRobertson
    August 16, 2018

    I'm suddenly struck by an apocalyptical world where the only thing that can save man-kind are analogue machines. That aside, I think it's really great to see the things that you create or set up having uses in actually helping people around the world. The other day when someone approached me with regards to business for their charity, I was very near giving them money instead of them paying me for my services!

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