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DRV8702-Q1EVM: The EVM get nfault when drving the load

Matthew Chen
Intellectual 1460 points

Part Number: DRV8702-Q1EVM
Other Parts Discussed in Thread: DRV8962, DRV8262

Hi team,

I am testing DRV8702 evm with Eload.. I use PH/EN mode, the duty circle of PWM is 100%. PVDD is 6.2V from buck-boost controller. the load is about 1.14ohm. When driving the load, the device get protected as below waveform. Vtepr is the output voltage of out2. OUT1 is 0V.  Is the problem from under voltage protect? Do you have any suggestion to solve this?

Matthew

  • 0
    TI__Guru 52185 points

    Hi Matthew,

    I assume you have enabled current regulation. You cannot connect a TEC directly to the output. Current regulation requires load inductance for controlled tON and tOFF regulation chopping cycles. You'll need series inductor. As well as to reduce ripple across TEC usually large capacitor 22uF or so would be required. 

    Does the buck-boost controller have a current limit? With 1.14ohm the current would be 6.2/1.14 = 5.43A for 100% duty. If PVDD falls below UVLO threshold the power supply must be improved.

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Intellectual 1460 points

    Hi Murugavel,

    Thanks a lot for your reply.

    I do drive the TEC using the DRV8702EVM, But I disable the current regulation by connecting the VREF to the AVDD pin. I have tested a higher voltage up to 24V, see below pic, there is a voltage drop when driving the TEC, it's only 20.8V, I think that the problem from Buck-boost controller.

    So do you mean the problem for DRV8702 get protected is from the UVLO?

    if I disable the current regulation, is the inductor still necessary for this device the drive the TEC?  

    is there any risk to disable the current regulation function for this device to operating?

    Thanks a lot 

    Matthew

  • 0 in reply to Matthew Chen
    TI__Guru 52185 points

    Hi Matthew,

    Thanks for the confirmation. If you have disabled internal current regulation then you must use < 100% duty cycle PWM probably with 100 kHz PWM frequency to have smaller inductor for LC filter. At 100% duty cycle you may be overdriving the TEC with no current regulation which may be demanding on the buck-boost controller.

    Regarding LC filters calculation for TEC you can refer to the TEC application example sections in these devices. DRV8262, DRV8962. There may be several other TI TEC driver examples, application notes and reference designs for you to look for LC filter details. 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Intellectual 1460 points

    Hi Murugavel,

    Thanks for your quickly reply.

    In my application, the DRV8702 is just used to change the direction of the current, that means one of the bridge will be fully on. The TEC voltage is changed by the output of buck-boost controller.

    DRV8262 and 8962 may not meet my requirement since I need current up to 21A. So the H bridge driver with external mosfet will be a good choice. I checked Drv8262 DDV datasheet, which says the peak current is 32A with single H bridge, can this device support my  applicaion here which is to drive the 24V21A TEC?

    Matthew 

  • 0 in reply to Matthew Chen
    TI__Guru 52185 points

    Hi Matthew,

    "In my application, the DRV8702 is just used to change the direction of the current, that means one of the bridge will be fully on. The TEC voltage is changed by the output of buck-boost controller.". I see. Then the burden is on the buck-boost controller. 

    "I checked Drv8262 DDV datasheet, which says the peak current is 32A with single H bridge, can this device support my  applicaion here which is to drive the 24V21A TEC?". The DVR8262 DDV in single H-bridge mode ( the two H-bridges are connected in parallel) the continuous current would be 20A. Proper heatsink design and a cooling fan may be necessary for driving this full-scale current which will be at the top end of what this device can deliver.

    Regards, Murugavel