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Transistor configuration for a heating mat (big load)

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massimoperdigo
Associate II

‎2024-03-11 09:11 AM - last edited on ‎2024-03-11 10:49 AM by

Hello everybody,

I am currently designing a configuration utilizing two drivers to heat a mat, which is a resistor load requiring 24V and 3.3A. This component is commuted at 100 Hz.

For this setup, I've employed two different drivers: the first one being VNB14NV04TR-E, utilized for switching large loads requiring high currents. On the other hand, I've utilized the MIC5018 to control the spoken driver. Additionally, I have add a pull-down resistor to force the 0 state, and I may use a series resistor for the PWM signal to limit the current, although I am not sure about it....

We have conducted tests of this configuration on one STM developmentboard, and it appears to be functioning properly. However, we would like to confirm if the setup is correct, as we have connected this system to a developed PCB with STM32h563, resulting in sparks and the MCU failure. The diode is a recent addition to the design; initially, we believed it might not be necessary due to the resistor load, assuming there would be no induction issues.

Apart from the current configuration, are there several circuit solutions and recommendations to prevent reverse currents or voltage spikes?

Thank you.

massimoperdigo_0-1710172951236.png

 

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Peter BENSCH
ST Employee

‎2024-03-11 10:48 AM

The VNB14NV04 will be switched on at a maximum input voltage of 2.5V and requires less than 150µA at the input. If you operate the STM32H563 with 3.3V, you can save the MIC5018 and connect the input of the VNB14NV04 directly to a push-pull GPIO of the STM32. However, I would also connect a real pull-down of 10...56kohms to the GPIO so that the input of the VNB14NV04 is safely deactivated at power-up and in other undefined states.

The freewheeling diode at the output may well be useful because the mat probably has zigzag conductors whose inductance should not be underestimated.

Please separate the high current paths including power GND from the control signals and their GND by means of a suitable layout or cable routing.

Hope that helps?

Good luck!
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

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Peter BENSCH
ST Employee

‎2024-03-11 10:48 AM

The VNB14NV04 will be switched on at a maximum input voltage of 2.5V and requires less than 150µA at the input. If you operate the STM32H563 with 3.3V, you can save the MIC5018 and connect the input of the VNB14NV04 directly to a push-pull GPIO of the STM32. However, I would also connect a real pull-down of 10...56kohms to the GPIO so that the input of the VNB14NV04 is safely deactivated at power-up and in other undefined states.

The freewheeling diode at the output may well be useful because the mat probably has zigzag conductors whose inductance should not be underestimated.

Please separate the high current paths including power GND from the control signals and their GND by means of a suitable layout or cable routing.

Hope that helps?

Good luck!
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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