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# TIDA-050017: Trouble understanding current flow

Part Number: TIDA-050017
Other Parts Discussed in Thread: LM5175

Hello,

I am looking into TIDA-050017 reference design together with TIDUCA8 to control my TEC element for cooling application and I am having some trouble understanding the current flow.

What I have:

• TEC is rated at 128.7W, 13.1A, 15.7V
• Vin = 12V from Lab Power Supply
• IC: LM5175
• How I connect my TEC: Vin -----------------------   +[TEC]-  ---------------------Vout

What I understand: according to the appnote, if I want to cool the TEC down, my Vout has to go to 12V+15.7V=27.7V and source current.

If so, how does the current flow through the TEC if my Vin is also sourcing the current? and how do I calculate the current through the TEC?

Side question: If I want to control 4 TECs of the same kind, can I get it done by connecting 2 TECs in series (Vdrop = 15.7*2 = 31.4) and use 1 cooling circuitry for each pair?

• Hi Takuchi.

thank you for using the E2E forum.

The TEC element is connected between VIN and VOUT.

So depending of the VOUT level relative to VIN, the TEC element see a positive or a negative voltage on its terminals.

Keep in mind: As the LM5175 is a BUCK-BOOST it can have the output voltage higher or lower then the input voltage.

Current through the TEC:

I(TEC) = (VIN - VOUT) / Impedance(TEC)

I am not the TEC element expert but I assume that if you put them in series there might be an mismatch between both and one is getting colder then the other.

I think connecting them in parallel could work.

Best regards,

Stefan