MAX1978 Peltier Controller - Unstable Output

Discussion in 'The Projects Forum' started by Argon_Ion, Sep 30, 2014.

  1. Argon_Ion

    Thread Starter New Member

    Sep 30, 2014
    This will be my first post, and the post is in regards to the first PCB I designed with the MAX1978 peltier controller. Here is a link to the datasheet from Maxim. My goal was to just create a board following the evaluation version (datasheet) circuit but exclude the extra DAC etc. from my circuit. I also wanted to use the chip at it's full rated 3 Amps rather than just 2.2 amps per the eval kit. To do that, the only change to the circuit was to switch the (R1) 0.068 ohm current resistor to a 0.05 ohm current resistor. Additionally, I am not using any of the onboard PID controller outputs, which are floating signals (Pins 14-24) and controller the output directly with the CTLI pin.

    When the board is setup to give full current (3.0A, bring both MAXIP, MAXIN to reference voltage), and the device is given signal to deliver full current to the peltier, the current instead of maintaining a 500 khz pwm signal, cuts out to 100khz and becomes unstable with audible buzzing. I presume it is an issue with the filter circuit but the parts I purchased are very similar to those spec'd in the eval version.

    Here is a link to both the board and the schematic. The board I realize is far from perfect but it was made, so I have to work with it.

    P.S. I do realize the circuit is essentially being used as a pwm driver/ h-bridge in one package, but I already purchased a few of the MAX1978's so I'd like to use them. I'm open to switching to another driver/h bridge as an option if someone could suggest one.

    Thank You,