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Selecting ADuM5230 Buffer Transistor

Hello,

Are you able to provide any advice on how I should select appropriate buffering transistors to sit between the ADuM5230 outputs and my MOSFET gates?

There aren't any example part numbers given in the datasheet or in any application note that I could find, and I don't have the background to be able to pick from among the many thousands that are available.

Thanks,

Doug McClean

Mass Bay Engineering

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  • Hello Alex,

    The ADuM5230 has and output current capability based on the size of the internal output MOSFETs. When driving the gate of the IGBT the gate driver is connected to, the amount of current available to drive that gate is limited by the combination of the internal resistance of the gate driver, and the external series gate resistor. When driving the external IGBT gate high, the gate driver is "sourcing" current. When the external IGBT gate is being pulled low, the gate driver is "sinking" current. The peak current of the internal MOSFETs are around 100 mA when sourcing, and 300 mA when sinking. If you attempt to get more current than that, you may be able to, but the internal MOSFET will eventually plateau and not give more than what the saturation current is. The current rating on the gate driver can be confusing.

    The ADuM5230 is special in that it delivers both isolated power and isolated gate drive in one, very small package. The available power that the ADuM5230 is limited mainly by thermal considerations, and for some low gate charge applications, this driver is a great fit. When the gate charge (or equivalent gate capacitance) is larger, the ADuM5230 can be limited in the switching frequency it is able to provide in the application. The 100 mA and 300 mA current ratings translate into slower rise/fall times than higher current gate drivers, but an external buffer stage can help increase the peak currents in sourcing and sinking.

    The ADuM5230 does not include deadtime control (or overlap protection). In a half-bridge topology, it is required that the user does not request that both IGBTs be on at the same time. This has to be ensured by external circuitry, or by the controller, as you have already noted. There are methods to produce deadtimes based on NAND gate structures, using RC time constants on the inputs. There are also some dedicated chips to convert a PWM signal into two signals with deadtime. I don't believe ADI has any of these deadtime generator chips right now.

    For the AUIRGB4062D1, the equivalent gate capacitance is around 5.1 nF. I got this from the datasheet by taking the maximum gate charge, and dividing by the driving voltage (15 V). Calculating estimated power for switching the AUIRGB4062D1 at 20 kHz, we get:

    C * V^2 * Fs

    5.1 nF * 15^2 * 20 kHz = 23 mW

    This is within the output power of the ADuM5230. In order to get faster rise and fall times at the IGBT gate, you can add a buffer as shown in the datasheet.

    RSchnell

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  • Hello Alex,

    The ADuM5230 has and output current capability based on the size of the internal output MOSFETs. When driving the gate of the IGBT the gate driver is connected to, the amount of current available to drive that gate is limited by the combination of the internal resistance of the gate driver, and the external series gate resistor. When driving the external IGBT gate high, the gate driver is "sourcing" current. When the external IGBT gate is being pulled low, the gate driver is "sinking" current. The peak current of the internal MOSFETs are around 100 mA when sourcing, and 300 mA when sinking. If you attempt to get more current than that, you may be able to, but the internal MOSFET will eventually plateau and not give more than what the saturation current is. The current rating on the gate driver can be confusing.

    The ADuM5230 is special in that it delivers both isolated power and isolated gate drive in one, very small package. The available power that the ADuM5230 is limited mainly by thermal considerations, and for some low gate charge applications, this driver is a great fit. When the gate charge (or equivalent gate capacitance) is larger, the ADuM5230 can be limited in the switching frequency it is able to provide in the application. The 100 mA and 300 mA current ratings translate into slower rise/fall times than higher current gate drivers, but an external buffer stage can help increase the peak currents in sourcing and sinking.

    The ADuM5230 does not include deadtime control (or overlap protection). In a half-bridge topology, it is required that the user does not request that both IGBTs be on at the same time. This has to be ensured by external circuitry, or by the controller, as you have already noted. There are methods to produce deadtimes based on NAND gate structures, using RC time constants on the inputs. There are also some dedicated chips to convert a PWM signal into two signals with deadtime. I don't believe ADI has any of these deadtime generator chips right now.

    For the AUIRGB4062D1, the equivalent gate capacitance is around 5.1 nF. I got this from the datasheet by taking the maximum gate charge, and dividing by the driving voltage (15 V). Calculating estimated power for switching the AUIRGB4062D1 at 20 kHz, we get:

    C * V^2 * Fs

    5.1 nF * 15^2 * 20 kHz = 23 mW

    This is within the output power of the ADuM5230. In order to get faster rise and fall times at the IGBT gate, you can add a buffer as shown in the datasheet.

    RSchnell

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