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Original question:

UCC14240-Q1: Output Voltage Is Not Regulated Properly

UCC14241-Q1: Over-temp shutdown

Qinghua Liu
Prodigy 240 points
Part Number: UCC14241-Q1

Tool/software:

Hi Steve,

Last time your recommendation to use UCC14241 to replace UCC14240 help us solve the issue of output not regulating. Now we have experiences another issue with UCC14241: the operating temp is much higher than we expected and sometimes it even triggered the over-temp shutdown at our standard thermal test with 40C ambient. In our application, the estimate load power of UCC14241 is about 1.5W. I have a question regarding to the input current draw (Ivin_on_no_load = 35mA, Max.) as shown in the UCC14241 datasheet section 7.6 Electrical Characteristics. Is that true that UCC14241 may draw 35 mA at idle no load?

Thanks,

Qinghua

  • 0
    TI__Mastermind 30725 points

    For the HVP052A EVM, the output is set to VDD-VEE-20V and you can see from the graph below, that the no load current consumption for 21V>VIN>27V is about 12mA. The max no load current consumption for 21V>VIN>27V shown in the data sheet is 35mA and is valid when VDD-VEE=25V. If you believe your output is shutting down due to temperature and not overload condition, we would need to closely consider the PCB layout and/or consider to replace UCC14240 ->UCC14241->UCC15241...UCC15241 is higher rated power but all three variants are p2p compatible. Please take a look at section 12.5 of the UCC14241 data sheet and pay attention to the use of thermal vias, use 2 oz copper top and bottom on the PCB. I have completed extensive temperature testing on these devices. Let me know your exact conditions and I will see what data was taken close to your configuration so you can have a better feel for what's possible with regards to temperature/max power.

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 240 points

    Hi Steve,

    Your feedback is very appreciated and sorry for my late update. I have changed to UCC15241 in our circuit and it looks have a little improvement but it still experiences shutdown. The estimated gate driver power is about 1.0watt, (power module gate charge ~0.5uC, gate voltage 17.5V/-2.5V, switching frequency 60kHz). The driver circuit is attached for your reference. In our thermal test, the ambient temp is 40C. When the shutdown happens, the UCC15251 top case temp is 111C. I agree with your recommendation that the thermal vias and copper layout surrounding this IC shall be optimized per the datasheet, but our current design makes it difficult to add more coppers and thermal vias. 

  • 0 in reply to Qinghua Liu
    TI__Mastermind 30725 points

    From what you provided P=Q*V*F=0.5uC*20V*60kHz=600mW but you also say the estimated gate drive power is ~1.0W...is it 600mW or 1.0W? Either way, neither is close to the max power capability at 40C. See section 5-11 of the UCC14240 EVM User Guide for thermal images at full load condition. Does the UCC15241 start up  as expected then shutdown after some time has passed or is it failing to start? How many are used in the system? How are you measuring 111C...thermal camera, thermocouple, something else? If this is for a three-phase inverter, are there 6x UCC15241 per inverter, one dedicated bias per gate driver? What does the RLIM configuration look like - are you using the RDR configuration highlighted in the Excel design tool? Can you send me the completed UCC15241-Q1 Excel sheet and your schematic showing the UCC15241+gate driver portion?

    Steve