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CSD16301Q2: Using CSD16301Q2 to drive a laser

PATRICK OHARA
Genius 3195 points
Part Number: CSD16301Q2

Hello,

I'm using a CSD16301Q2 to drive a simple Laser. I chose the CSD163 because I wanted voltage controlled MOSFET to drive the gate from a GPIO on my CC2640r2. The gate voltage when turned on is 3.0VDC with the battery providing 4.5VDC. With the gate pulled to 3VDC I expect that the CSD163 will pass up to 20mA (limited by the 220 ohm series resistor). When I apply 4.5 volts to the laser with a bench power supply, it draws 11.8mA. Please have a look at my implementation shown below and let me know what I'm doing wrong.

Thanks,

Patrick

  • 0
    Genius 3195 points

    Sorry, I described the set up but didn't describe the problem. With 4.5VDC applied to the circuit shown above, I get 2.4VDC at around 10mA on the laser terminal. Of course this is inadequate to drive the laser. I know that MOSFETs are generally used for higher power applications, but I wanted the voltage controlled behavior. Is there any reason that the CSD16301Q2 should not work under these circumstances?

    Thanks,

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 32345 points

    Hi Patrick,

    Thanks for your interest in TI FETs. I don't see any problems with your schematic and set up. I would recommend measuring VGS and VDS of the FET to make sure you're getting the voltages you expect. With VGS = 3V, the FET should be on - rds(on) is 27mOhm typical - and you should see a very small voltage drop from drain-to-source. Does the laser have some impedance across its terminals where you connect it to J2? With 4.5V and 11.8mA, I calculate the total resistance across the battery is 381 ohms. Assuming the FET is on, you have 161 ohms of resistance in addition to the 220 ohms. I hope this helps resolve your problem. Let me know if you have additional questions.

  • 0 in reply to John Wallace1
    Genius 3195 points

    Hi John,

    Thank you for your comments and confirmation that I seem to be implementing this device correctly. When I connect the laser module to a lab grade power supply at 4.5 volts it consumes 11.8mA. In my circuit I include a current limiting resistor (220 ohms). As a result the voltage at the laser module is only ~1.9 volts. This likely is why the laser output is so low. The module seems to include it's own current limit. Do you see any problem removing the current limiting resistor?

    Thanks again,

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 32345 points

    Hi Patrick,

    If you're certain the laser has adequate current protection, I don't see a problem removing or reducing the current limiting resistor. To be safe, you may want to try to reduce the value first before actually removing or shorting out the resistor.