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DRV8837: Controlling multiple latching solenoids and relays

Part Number: DRV8837
Other Parts Discussed in Thread: DRV8839,

Hi 

I need to control about 8 latching solenoids and relays, therefore i have originally used 8 DRV8837, as shown in the first image below.

  

I would like to know would it be possible to achieve controlling all 8 solenoids/relays using only 5 Driver ICs as shown below. At any given time only one solenoids will be controlled, therefore i have common drive signal and multiple enables.  So when the common driver signal is HIGH and only the appropriate other driver is enabled, it would operate solenoid. But if the other pin on driver is also HIGH but a slightly lower voltage to the COMMON drive signal, what effect would that have? 

Or would the DRV8839 be better options as each output can also be set to Z if i am correct, while on DRV8837 this not possible unless both are Z?

  

Thank You

  • Hi Dharmesh,

    Your 5 device configuration should work, but appears to need a small edit.

    HBRIDGE_OUT3 should not be on U2, and should be moved to U21 to the HBRIDGE_EXTRA location.

    The reason is that the solenoid/relay shown connected to U2 HBRIDGE_OUT3 will always be switched driven when trying to control one of the other relays.

    Using the DRV8839 removes this issue. Deciding to use the DRV8837C vs DRV8839 is really a cost question. The DRV8837C price is less, and the GPIO resources required are also less.

    If you decide on the DRV8837C, the HBRIDGE_COMMON should be enabled prior to enabling  and after disabling the solenoid/relay connection. If not, it may be possible for the two solenoids/relays to both switch (depending on the voltage).

  • Dear Rick

    Thank You for your reply

    Yes i agree this was an error, therefore i have moved H-Bridge_Out3 onto U21, so i have a total of 8 solenoid instead 9. Which is fine.

    I have a common IN1 and IN2 for all devices. If i am correct on U2, should have an independent signals?

    Can there be a possibility that H voltage might a little difference among the  DRV8837C, drivers? For example if H-Bridge_Common Is High(5V). and H-BRIDGE_OUT5 is Low(0V) ,but HBridge_OUT7 is High(4.9v). Would this mean a little current would follow into OUT7 as well?

    Please explain how two device would be switched ON if its not enabled prior? Are the output not in high impedance mode?

    Regards

    Dharmesh

  • Hi Dharmesh,

    I have a common IN1 and IN2 for all devices. If i am correct on U2, should have an independent signals?


    I think you need independent signals on U2 to get the correct current flow.

    Can there be a possibility that H voltage might a little difference among the  DRV8837C, drivers? For example if H-Bridge_Common Is High(5V). and H-BRIDGE_OUT5 is Low(0V) ,but HBridge_OUT7 is High(4.9v). Would this mean a little current would follow into OUT7 as well?


    Yes, there could be some current flow in the case above. But typically you will need more voltage/current than 0.1V/xmA to latch the solenoid/relay.

    Please explain how two device would be switched ON if its not enabled prior? Are the output not in high impedance mode?


    The case I am referring to is similar to your question above. If you enable H-BRIDGE C, H-BRIDGE OUT5 is high and H-BRIDGE OUT7 is low. If common is not enabled yet, the current will flow from H-BRIDGE OUT5 through load 5 to the common and from the common through load 7 to H-BRIDGE OUT7. This will create a voltage of approximately VOUT_DCDC/2 across both solenoids/relays.

    Depending on the specs of the loads, this may be enough to change the state of the latching solenoid/relay.

    By setting the H-BRIDGE COMMON output and enabling the output prior to enabling the desired load (H-BRIDGE ENB x), this scenario is avoided.

  • Hi Eric

    Instead of minimising on component usage,i think it would be best to keep each H-Bridge Independent for each relay/ solenoid.

    Please correct me if i am wrong, but if i was to have one relays/solenoid with high resistance, and then a low resistance device then it could be possible that both could be activated at same time.

    E.g. if H-Bridge Common is Low,H-bridge 3 is High and H-Bridge 5 is low. Then when the current is flowing from OUT 3 to to COMMON, could also active or deactivate a device on out5, if it is lower powered. Would this be correct.

    At this stage i do not know what relays or solenoid will be used. 

  • Hi Dharmesh,

    E.g. if H-Bridge Common is Low,H-bridge 3 is High and H-Bridge 5 is low. Then when the current is flowing from OUT 3 to to COMMON, could also active or deactivate a device on out5, if it is lower powered. Would this be correct.

    It is unlikely the device on H-Bridge 5 would activate/deactivate based on your connections. The voltage from H-Bridge 5 to H-Bridge Common would be very small. There should not be enough voltage/current to activate/deactivate the load on H-Bridge 5.

    It is important to check the relay/solenoid specifications, but most require a minimum voltage (current) to activate.

  • Dear Rick

    Thanks

    One last question , are drv8837c and drv8837 both identical with exception of their current output limit? 

  • Hi Dharmesh,

    The devices are similar with a few exceptions related to current:

    The DRV8837 has lower RDSon, allowing more current before thermal shutdown.

    The DRV8837 has a higher overcurrent protection trip point, which can be valuable if capacitors are connected across the load.

  • Ok . I am to drive 300ma solenoids or latching relays for about 400ms. I guess both would give me similar results or same operational function.

  • Hi Dharmesh,

    You are correct. You should see similar results at 300mA.