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UC1707-SP: Input voltage levels

Emilio Fazzoletto
Intellectual 285 points
Part Number: UC1707-SP

Hi everybody!

I'm using a UC1707-SP Dual-Channel Power Driver (part number 5962-8761901V2A) for a high-reliability, spaceborne system.

In my application, it's driven by a microcontroller, with two 0÷3.3V PWM signals, and drives two power MOS.

The PWM signals are isolated: they go through 1:1 transformers which are placed between the microcontroller and the MOS driver.

The problem is the loss of the DC components of PWM signals due to transformers. The PWM signals at UC1707-SP inputs have -1.65÷+1.65V levels.

I tested the UC1707-SP in this condition and it seems to work properly, despite the fact that the required "Digital input high level" is 2.2V (by datasheet).

Do you think that this configuration is "doable" (after more extensive tests to prove it works) or that it's unacceptable?

Thanks in advance,

EF 

 

  • 0
    TI__Genius 14540 points
    Hi,

    We have received your inquiries on the UC1707-SP. The applications engineer responsible for this device will be in touch very soon.

    Regards,
    Christian
  • 0
    TI__Mastermind 21965 points

    Hey Emilio,

    To begin, unfortunately TI cannot guarantee the performance of the part that doesn't get the required signals.

    The 2.2V requirement is for you to be sure all devices that you use will work as there will always be variation from part to part.

    Another reason to supply the part with a 2.2V signal rather than a 1.65 V signal is that I noticed there is an inverter and or gate at the input of the parts:

    The transistor level for the inverter should look like:

    What radiation will do to the part is degrade the Beta of the transistor or if its a MOSFET make it harder to turn on. In either case the part will want a higher input the more radiation that effects it. The device is known to be 50krad radiation tolerant under the conditions in the datasheet(the 2.2 Volts) so 2.2 Volts could help prevent problems that could arise due to radiation.

    Thanks,

    Daniel

  • 0 in reply to Daniel Hartung
    Intellectual 285 points

    Daniel Hartung said:

    Hey Emilio,

    To begin, unfortunately TI cannot guarantee the performance of the part that doesn't get the required signals.

    The 2.2V requirement is for you to be sure all devices that you use will work as there will always be variation from part to part.

    Another reason to supply the part with a 2.2V signal rather than a 1.65 V signal is that I noticed there is an inverter and or gate at the input of the parts:

    The transistor level for the inverter should look like:

    What radiation will do to the part is degrade the Beta of the transistor or if its a MOSFET make it harder to turn on. In either case the part will want a higher input the more radiation that effects it. The device is known to be 50krad radiation tolerant under the conditions in the datasheet(the 2.2 Volts) so 2.2 Volts could help prevent problems that could arise due to radiation.

    Thanks,

    Daniel

    Dear Daniel,

    thanks for the quick, clear explanation.

    Just another request: could you provide an estimation regarding the degradation rate of the input stage (given a radiation dose)? Something like +100mV on the threshold level per month (@50krad).

    Thanks again,

    EF

  • 0 in reply to Emilio Fazzoletto
    TI__Mastermind 21965 points

    Hey Emilio,

    All of our radiation data for the part is available here:

    The test that you want to look for are on pages 20 and above for looking at the input voltages and the current. From the tests it looks like the voltage changes were smaller (around 2.5% max) however the current changes were significant. There was one 40krad test for IIL of the inverting input of B that went from -0.639 to -0.706 ma.

    The part is 50krad tolerant which means that the device when tested did not go out of spec given that level of radiation even if there were changes. I only bring up the radiation because you are planning on going below the specified level and I want to show there are more dangers than us not guaranteeing the part.

    Thanks,

    Daniel

  • 0 in reply to Daniel Hartung
    Intellectual 285 points
    Thanks again for the clarification!
    EF