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LM3648: Thermal shutdown mode

Henry Wang3
Expert 2875 points
Part Number: LM3648
Other Parts Discussed in Thread: LM36010, LM2759

Hi Sir,

If the LM3648 is in thermal shutdown, even if the die temperature is lower than 150°C, the LM3648 is not available for operation until there is an I2C read of the Flags1 Register and doing a read action, the Flags1 register is cleared, right?

My customer wonders why  LM3648 should be designed with such a protection mechanism?(I mean need an I2C read)
They hope when the die temperature has lower than 150°C condition, the LM3648 can recover to normal operation automatically.

  • 0
    TI__Expert 6440 points

    Hi, 

    It is because when the die temperature is higher than 150C, the device will enter TSD to avoid damage, and if it will recover to normal operation automatically, it may enter the TSD again, so the mechanism is used to make sure the operation environment is proper and recover the normal mode again.

    So my suggestion is to read the register continually at intervals to make sure the device can back to normal mode.

    And I'm also curious about the customer's application, does it can cause TSD easily?

    Thanks!

    Ives Li 

  • 0 in reply to Ives Li
    Expert 2875 points

    Hi Sir,

    You're right, it does cause TSD easily.

    Their conditions are V-in = 5V; V-out = 3.2V; I-in = 0.9A; I-out = 0.9~1A; LED_vf = 3.2V.

    Do you have any advice to avoid TSD?

    Or suggest another LED driver device? (need I2C, buck topology, low V-in, not use TSD)

  • 0 in reply to Henry Wang3
    TI__Expert 6440 points

    Hi Henry,

    If it is easy to cause TSD, the device could be damaged if doesn't enable the TSD function.

    TSD is also the basic protection for our devices, so I cannot suggest you a device which doesn't have this function.

    So, we can only try to reduce the ambient temperature or improve the PCB layout to lower the chip temperature.

    Besides, we have LM36010 which has same function as LM3648, but it also has TSD function.

    Thanks!

  • 0 in reply to Ives Li
    Expert 2875 points

    Hi Sir,

    Thank you for your clearly explaining.

    May I have another question, could you advise a replacement device for APW7502?

    APW7502.pdf

  • 0 in reply to Henry Wang3
    TI__Expert 6440 points

    Hi Henry,

    Could you please provide below information so I can suggest you suitable device for your application"

    1. Vin (Power supply voltage for LED driver)

    2. VLED (How many LED in series) 

    3. Iout (constant/flash current for your LED)

    4. Interface (only I2C or can accept GPIO/PWM)

    5. How many channels you need (I guess you only need to drive1 LED)

    Thanks!

    Ives Li

  • 0 in reply to Ives Li
    Expert 2875 points

    Hi Sir.

    Please refer to the below conditions.

    1. Vin (Power supply voltage for LED driver) => 5V

    2. VLED (How many LED in series) => 1 LED in series

    3. Iout (constant/flash current for your LED) => 1A

    4. Interface (only I2C or can accept GPIO/PWM) => on;y I2C

    5. How many channels you need (I guess you only need to drive1 LED) => 1ch

  • +1 in reply to Henry Wang3
    TI__Expert 6440 points

    Hi Henry,

    For your application, it seems LM2759 is the most suitable device, because it doesn't have TSD function and can meet your operating condition.

    Thanks!

  • +1 in reply to Ives Li
    Expert 2875 points

    Hi Sir,

    Thank you for your advice. It is so helpful to me.

  • 0 in reply to Henry Wang3
    TI__Expert 6440 points

    You are welcome！