Post Go back to editing

ADN8834 Calc RC and RV for V and I limits of TEC

UG-858  has table 1 on page 3 to calculate RV1 and RV2, but sets abitraily RV2=10k which doen't work for most TECs.

Similarly table 2 on page 4 shows RC1 and RC2 for pre-established current ratio.

Equation for flexible V and I ratio shall be supplied and may look like:

Say desired VTECMAXCool = 1.4V,  VTECMAXHeat=1.0V

Because of the Avlim=2V/V, one finds

VLIMcool= 0.7V and VLIMheat=0.5V

Since Isink_Vlim = 10uA, one can find

RVp = RV1||RV2  =  (VLIMcool - VLIMheat)/Isink_Vlim =  (0.7-0.5)/10u =  20kohms

also

Vratio=RV1/Rv2=(Vref-Vrv1)/rv1=1.8V/0.7V=2.57

Then one can calculate

RV1 = RVp * (1+ Vratio) = 71.4 kohms

RV2 = RVp * (1 + 1/Vratio) = 27.8 koms

Same principle can be applied for RC1 and RC2  where the Isink_Ilim=40uA. 



Corrected with Vratio
[edited by: Optobru at 7:41 PM (GMT -5) on 7 Feb 2022]
Parents
  • Hi Optobru,

    Thanks for posting here. 
    Yes, the table in the user guide suggest values of the resistor divider that gives TEC voltage limit that has same magnitude for cooling and heating. This is for easy suggesting values for the users. This may not work at all times for customer who wants different magnitude of TEC voltage limit but this table is beneficial to others. They can always go back to the equation you used to compute for the resistors if they want to use different magnitude of voltage limit at each mode. Same with the current limit. 

    I really find this suggestion of yours helpful. This really simplifies using the series of equation for computing the resistor values. I also checked your derived formula and find it correct. Thank you so much for this input.

    Regards,

    Noel

Reply
  • Hi Optobru,

    Thanks for posting here. 
    Yes, the table in the user guide suggest values of the resistor divider that gives TEC voltage limit that has same magnitude for cooling and heating. This is for easy suggesting values for the users. This may not work at all times for customer who wants different magnitude of TEC voltage limit but this table is beneficial to others. They can always go back to the equation you used to compute for the resistors if they want to use different magnitude of voltage limit at each mode. Same with the current limit. 

    I really find this suggestion of yours helpful. This really simplifies using the series of equation for computing the resistor values. I also checked your derived formula and find it correct. Thank you so much for this input.

    Regards,

    Noel

Children
No Data