I have a TEC control circuit/pcb that I'm trying to debug and understand. It's not my design but I'm trying to learn what it's doing so I can use it for my own purposes. I've attached the schematic.

I'm quite confused about a couple of things. I'll start off with 2 questions or observations I noticed:

1) If I remove the LM5101 driver, the TOUT+ and TOUT- lines both have a small voltage. I kind of expected this to be around 0V. Is the voltage I'm seeing on these lines coming from the bootstrap capacitor or D16/D14? I expect the bootstrap cap at DC to be an open circuit.

2) When the LM5101 is soldered on, and all 0s are input to the driver (ie. no mosfets on), I am still seeing voltages on TP13 and TP15. This is causing the mosfets to turn on partially and I'm seeing ~10-12V on the TOUT+ and TOUT- lines. I'm wondering why these two FETs are being partially turned on even though I am inputting zeroes into the LM5101. I'm also curious as to why the voltage at TOUT+ is around 1-2V different than TOUT-. I assume the FETs are not turning on equally.

Thanks for the help!

 

I'm also having trouble getting the h bridge to outpout 0 volts. If I try turning both low side MOSFETs on, I don't get 0v. Am I not supposed to turn both low sides on?

 

1) If I remove the LM5101 driver, the TOUT+ and TOUT- lines both have a small voltage. I kind of expected this to be around 0V. Is the voltage I'm seeing on these lines coming from the bootstrap capacitor or D16/D14? I expect the bootstrap cap at DC to be an open circuit.

The LM5101 could be damaged, but you still can try it using another way.

When you remove the LM5101, also release the LOAD, then measure TOUT+ an TOUT-, if these two points still have voltages, then you can discharge the C80(220u/35V), and also discharge another cap probably is C82(220uf/35V) which connected with C81, and then measure TOUT+ an TOUT- again.

LM5101 : connected the 1,5,6,7 pins, and release the 2,3,4,8 pins, and measure the voltage of 2,3,4,8 pins, you also do the same thing with another LM5101.