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Driving TEC (peltier) module (15V/4A)

Other Parts Discussed in Thread: DRV8840, DRV8412, DRV8844

Hi,

I am planning to use DRV8840 to drive CUI CP40336 peltier module, is DRV8840 even good choice?

Is there any application notes or guidelines how to drive TEC module and what should be taken care?

This is my first project with TEC modules.

Thanks,

MikkoCUI_CP40336.pdf

  • Hi Mikko,

    The DRV8412/32 and DRV8844 are the two popular choices to drive TEC modules. The DRV8412/32 datasheet includes details on driving TEC modules.

    Both DRV8412/32 and DRV8844 can be PWM'ed at higher frequencies than the DRV8840. The DRV8412/32 can achieve up to 500kHz PWM.
  • Hi Rick,

    Thanks for fast reply!
    I checked DRV8412/32 datasheet, there is only Application Diagram Example for TEC Driver Schematic.
    I am looking also some document which describes how TEC modules shall be driven (eg why 500kHz is better than 100kHz).
    Is there any document for that?

    -Mikko
  • Hi Mikko,

    There are typically two advantages to higher PWM frequencies.

    The first is that the voltage across the TEC can be controlled more tightly.

    The second is that in some cases the inductor size can be reduced.

    The app note provides some information, although it does not apply directly to the DRV8412.

  • Hi,

    Now we are testing circuit (DRV8412, circuit is very similar than in datasheet Figure 17)

    E225 PCB Schematic Peltier.pdf

    We have some problems with circuit,

    10% pwm steps up or down are working.

    20% pwm steps or more is not working, fault situation is occurred. I guess it was over current fault because only Fault LED went on.

    Then we changed OC_ADJ to 23kohm and still same same fault occurs. 

    It's not clear that is driver working in CBC mode or OC mode. 

    Could you help with these issues? below you'll find the schematic, 2 TEC elements (CP40336) are connected in series to output of the driver.

    Additionally when I am driving this bi-directional driver from cooling 10% --> heating 10%,  is also not working (see picture below, ch3-4 output, ch2 PWM_A), but this is not causing fault.

    ch3 is going low as it should be but then after ~15us it goes up, kind of floating.

    Is datasheet chapter 7.4 correct,

    Is CBC mode used in modes 1,2,4 or 1,3,4?

    If it is 1,3,4 then we have to follow next text since we are using mode 3 (PFB):

    "In operation modes 1, 2, and 4 (CBC current limit is used), once the CBC current limit is hit, the driver will be
    deactivated until the next PWM cycle starts. However, in order for the output to be recovered, the PWM input
    corresponding to that driver in CBC must be toggled. Because of this, CBC mode does not support operation
    when one half-bridge PWM input is tied to dc logic level."

    I do not understand last 2 sentences (bolded), could someone write this clearer?

    -Mikko

  • Hi Mikko,

    Sorry for the delayed response. Cycle by cycle is used in modes 1, 3, and 4. In your schematic, you are using mode 3 (PFB with CBC)

    In PFB CBC mode, the outputs will disable if the current limit is reached. The outputs will remain disabled until both inputs are toggled. It is recommended to add a small 100ns pulse on the opposite PWM input to re-enable the outputs.

    For example PWM_A is PWM'ed at 95% duty cycle at 200kHz (4.75 us on/.25us off). At 4 us into the period, the CBC activates. The outputs are disabled. To re-enable the outputs, toggle PWM_B high for the last 2% of the period (100ns).
    If PWM_B is not toggled high, the outputs will not re-enable.
  • Hi,

    If PWM_A is toggled 10-90%, is it mandatory toggle PWM_B every cycle end to re-enable outputs or would it work if PWM_B is togled example every 10th cycle?

    Our system is running by 500kHz and it means that minimum duty for re-enable PWM_B pulse is 3% (60ns) If we are driving TEC's 90% duty and then 3% for re-enable -> This means that we are actually having 87% duty.   Maybe we could decrease frequency from 500kHz to 250kHz, What would be recommended frequency for TEC that ripple is still enough low? 

    I have understand if 120kohm OC resistor is used then OC limit is 2.4A (in PFB mode 4.8A), is this correct?

    What is the current value when CBC starts limit current when 120kohm OC resistor is used

    What is the recommended OC resistor value for our 3A TEC's?

     

    -Mikko

  • Hi Mikko,

    PWM_B should be toggled every cycle. If you toggle PWM_B every 10th cycle, the outputs could be disabled on the first one and remain disabled for the next 9 cycles.

    With a 120kOhm resistor, the OC_ADJ activates between 4.32 and 5.28A (+/- 10% variation). The OC_ADJ feature is designed for system protection and not for precise current control. It can vary by 20% from device to device, and the resistor tolerance can have an impact.

    The system design (capacitors on the outputs) can also affect the CBC.

    If you have tight control of the currents through your control loop, the OC_ADJ can be set higher such that it is used as system protection only. By doing this, you could then use the full PWM frequency range.