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DRV8844EVM: Driving three fast acting 1A solenoid valves by providing analog input signals

Mehmet Tomac
Prodigy 50 points
Part Number: DRV8844EVM
Other Parts Discussed in Thread: DRV110, DRV8844, DRV8860

Hello. I'm sorry I'm not very knowledgeable in electronics so I need help to understand two things about using DRV8844EVM. 

1- I just bought DRV8844EVM. I want to drive 3 high speed solenoid valves (Festo MH3) each rated at 1A. I have a NI DAQ system where I can create three square wave analog output signals as the inputs for 8844. But I found out that there is something callled PWM where the duty cycle is adjusted in 8844. My question is I'm already sending square wave analog signals that has frequency, duty cycle, phase info in them. So how PWM will affect my inputs. No matter what duty cycle I send through my analog square wave, 8844 will use PWM duty cycle? I'm bit confused.

2- Also when I use all my valves the total current through 8844 might be as high as 3A. This will create some heat. So should I use 8844 let's say 30 seconds and the wait till it cools down or it is designed to be used continuously?

Thank you very much for the help.

  • 0
    TI__Genius 14487 points
    Hi Mehmet,

    1) While some of our motor drivers do PWM on the output automatically, this one does not. If you want to use PWM with this device, you need to provide the PWM signal input from your NI DAQ. Anytime you vary the duty cycle of a square wave for the purpose of control, it is PWM (pulse-width modulation).

    2) You will have to check your valves' datasheets to understand how you can drive them and what voltage rating they have. Typically a 24-V valve can be driven with 24-V continuously. If your valves are getting hot, you can solve this problem by providing the full voltage for ~100 ms to ensure the solenoid pulls in, then you can PWM at about 50% to operate the valve at a lower current during the holding time. This should allow it to run cooler. The DRV110, DRV101/2/3/4, and DRV8860 all have this kind of "Peak and Hold" function for driving valves, but you can do it with the DRV8844 and the NI DAQ also.
  • 0 in reply to James Lockridge19
    Prodigy 50 points
    Hi James,
    This is great thank you. But I have still two things to be clarified.

    1- Yes I do the PWM with my square wave analog signal before 8844. If I don't provide any PWM signal input from my NI DAQ to the 8844 then it will just use the square wave analog signal that I provide to the inputs of 8844. Is this correct understanding?

    2- The heat generated by the valves are usually okay with my current setup but I'm mainly worrying my new driver 8844 will heat up and burn since the total current is high. What I was trying to ask was if 8844 is going to be okay for continuously work at high currents.

    Thank you very much for the help!
  • 0 in reply to Mehmet Tomac
    TI__Genius 14487 points

    Mehmet,

    1) Your understanding is correct. Just to clarify, the square-wave signal you provide from your NI DAQ is technically a PWM signal.

    2) The DRV8844 has overtemperature and overcurrent protections, so the device will shut off automatically if it gets too hot or has too much current. It should be fine to operate in your conditions. You may want to consider attaching a heat sink to the device if you are concerned it will be too hot. for the most part, the board design should dissipate much of the heat since you are using the EVM.