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LM5101A: Short issue in HS and GND

Part Number: LM5101A
Other Parts Discussed in Thread: LM5101

Hi TI Team,

I am facing LM5101A HS and GND short circuit issue. I need your support to resolve. I will share all data by mail. Kindly support by offline.

Regards,

Kubendran

  • Hi, Kubendran,

    Sorry to hear you are having issues with your design.

    For faster support, please reach out to your assigned local TI FAE.

  • Hi Sir,

    Thank you for your reply. In Lm5101 datasheet page no 7 ,figure 2, showing 4.4nF load at 300 KHz IDD current approximately 20mA. What it tells either maximum IDD current?

    From datasheet LM5101 WSON 10 package thermal resistance 40 deg/W. We are using PCB size 60*58*4.3 (All are in mm) copper thickness 3OZ. total layer 18Nos Tj-150deg ,Ta-25deg, How much power LM5101 will dissipate?

    Kindly reply.

    Regards,

    Kubendran

  • Hello Kubendran,

    For the 1st question, the curve Figure 7 shows the IDD current Vs frequency for various capacitance loads, for 300kHz and 4.4nF it does show somewhat less than 20mA. There are Typical Characteristics curves so it is measured data from test devices, not necessarily worst case for all devices. The current will be dominated by the capacitive load and operating frequency so the maximum current will not vary significantly. 

    For the question about power dissipation, the thermal resistance of 40 degC/W is based on a board described in Note 2: 4 layer board 1.5, 1, 1 , 1.5 Oz and 50mm x 50mm power and ground planes embedded in PCB. With a max recommended Tj of 125 deg and ambient of 25 deg, there is a 100 deg allowed rise. the power would be 100 degC/(40degC/W) or 2.5W. If you assume the 150 deg abs max the power would be 125/40= 3.125W.

    This device package does provide good thermal performance.

    Confirm if this addresses your question, or you can post additional questions on this thread.

    Regards, 

  • Hi Sir,

    Thank you for your quick reply. If load capacitor more than 10nF at 300KHz what will be the effect of IDD current ,it will damage the driver IC?

    Regarding power dissipation: Datasheet mentioned thermal resistance 40deg C/W  it will dissipate 2.5W if Tj=125 deg.  But whereas my PCB size different which is mentioned in last post, in this case how much power LM 5101 will dissipate?

    Regards,

    Kubendran

  • Hello Kubendran,

    The driver current from driving a capacitive load can be determined by  C x VDD x Fsw, for 10nF (x2 drivers, this will be 20nF x 12V x 300 kHz will be 72mA. One thing to watch on the average current is the average current maximum for the boot diode is 100mA. So make sure the average current required for gate drive losses on the HO output  does not exceed 100mA.

    For the thermal question regarding your board size, I think the size of the GND and VDD planes mentioned in the datasheet board description impact the thermal resistance, not the overall board size. I would determine the size of these planes to see how it compares to the 50 x 50mm of the test board description.

    Confirm if this addresses your questions, or you can post additional questions on this thread.

    Regards,