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LM5113: lm5113

Bob Rowland
Prodigy 180 points
Part Number: LM5113
Other Parts Discussed in Thread: LM5025, LMG1205, LMG1210

We are developing a product which will use the LM5113 to drive FET half bridge which will drive a heater. We will actually be using two of these configurations to create a full bridge. We used the EPC9049 development board to test the circuit and it works great. We are about to add it to the board layout but have a couple questions. In figure 18 of the LM5113 spec sheet there is a parallel diode / resistor on each of the LM5113’s inputs. This diode & resistor are also on the EPC development board. We tried removing the diode and resistor and it had no effect on the performance of the circuit. Can you tell me what the purpose is of the diode and resistor on the two input? The other question is related to shoot-through. The EPC9049 development board has two gates driving the HI and LI inputs, but it doesn’t appear they are doing anything to eliminate shoot-through. Does the LM5113 add any delays to the outputs to protect against shoot-through or is this something we should handle? We would like to eliminate the two gates and drive the two inputs from separate clocks, but if shoot-threw is a potential problem we will need to modify the two clocks which could be difficult to do. Our system is extremely sensitive to noise and shoot-through would be a source of noise.

Thanks,

 Bob

  • 0
    TI__Genius 12990 points

    Hi Bob,

    Thanks for reaching out on e2e about LM5113 and sharing your application info.

    For your first question check out this thread this goes over something similar.

    The LM5113 datasheet uses LM5025 as a controller which has drivers internal to the controller. The resistor and parallel diode is there on the output of the LM5025 to be able to fine tune the input to the LM5113 (specifically turn off). The diode allows a full turn on speed from the controller output and 5113 input and allows the 0R resistor to be populated with a larger resistance to allow a slower turn off speed at the input of the 5113. Let me know if this does not make sense or you have any other questions about this.

    LM5113 requires the controller or external circuitry to take care of the independent input signals to make sure they do not overlap. The controller can make a predefined or adjustable dead-time or external components like a low-pass filter at the input or a gate resistor to slow the output can be added to make sure there is enough dead-time and prevent shoot through. The low pass filter or gate resistor needs to be tuned during system operation to achieve the best trade off of dead-time, shoot through and conduction loss.

    For concerns about shoot through due to lack of dead-time I highly recommend to check out LMG1210 (an updated version of LM5113 and LMG1205) which has controllable dead-time to help prevent shoot through as well as over charging the bootstrap.

    let me know if you have any other questions!

    thanks,