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Original question:

Can ISO5852S support to 60khz switch frequency

ISO5852S: External gate current buffer circuit requirement

Rajasekaran
Intellectual 945 points
Part Number: ISO5852S

Hi,

We are working with inverter designing for motor drive application..

Our preferred IGBT is SKM100GB12T4. Its gate capacitance Qc = 565nC at Vge=-8V to 15V.

switching frequency : 20kHz, Gate resistance Rg = 10 Ohm, . Internal gate resistance : 7.5 Ohm

Average gate current : 11.3mA and peak gate current is 1.3714A

Power required per channel is 271.19mW.

1. Shall we use ISO5852S to drive this IGBT or do we required external gate current buffer circuit? 

2. How to calculate the values for Rg (on) and Rg  (off)  in ISO5852S ?

Kindly confirm the details to proceed further.

Thanks & regards,
Rajasekaran

  • 0
    TI__Expert 4875 points
    Hello Rajasekaran,

    In Section 10.2.2.9 you will see Equation 5 which is used to calculate the actual dynamic output power of the driver. The maximum Ron and Roff are also given here, as 4-ohm and 2.5-ohm, respectively. Notice that these resistances are given when the driver is fully on or off, so the transient resistance may be lower, however using these will give you the maximum resistance for calculating the power dissipated in the driver.

    Using that equation and your given specifications, the dynamic output power with load will be 40.42-mW. This is sufficiently below the maximum power rating of ISO5852S, which is 251-mW at 125C ambient temperature. Thus, you will have sufficient margin to drive your device given the operating conditions. Additionally, based on your gate resistance (10-ohm), the internal gate resistance (7.5-ohm), the maximum driver on/off resistance (4-ohm/2.5-ohm), and the drive voltage (23-V), the ISO5852S also has sufficient peak current to meet those drive requirements. You may consider a buffer circuit to speed up the turn-on or turn-off time if you are concerned with switching losses. However, given your specifications, the ISO5852S meets the requirements for driving your device.

    Please let us know if you have further questions.

    Regards,
    Audrey
  • 0 in reply to Audrey Dearien7
    Intellectual 945 points

    hi,

    I am trying to simulate ISO5852S gate driver in Orcad PSPICE software.  we created the circuits with and without current buffer circuit.

    we used IRF840 switch and when  we used current buffer circuit, it takes less gate current compared to without current buffer circuit.  We need to replace the IRF840 with SKM100GB12T4 IGBT model.  

    circuit with current buffer

    circuit without current buffer

    (Red color for gate current without buffer circuit and green color  for gate current with buffer circuit)

    Could you please guide us the reason for the variation in the gate current (for same switch with same frequency & duty cycle)

    Thanks & regards,

    Rajasekaran

  • 0 in reply to Rajasekaran
    TI__Expert 4875 points
    Hello Rajasekaran,

    In your circuit simulation with the current buffer, please connect OUTH and OUTL, as shown in Figure 57 in Section 10.2.2.11 of the datasheet, and then connect to the gates of the BJT buffer. The current peak output with the current buffer, as you said, should be higher based on the resistors in series with the BJTs.

    Regards,
    Audrey