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TPS7A49: current limit behavior question

Genius 4310 points

Replies: 1

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Part Number: TPS7A49

Hi there,

we use TPS7A4901 in 19V--->12V application, normal I_load is 100mA or so. We have some questions to consult on its current limit behavior in case of over load current occurs.

Quote: "section 8.3.1 and 8.3.4 of datasheet. The maximum amount of current the device can source is the current limit (309 mA,typical), and is largely independent of output voltage."

1. IF during test we intentionally set a large CONSTANT I_load of 1A, we would see the I_out be limited to 309mA(typical) according to section 8.3.1, and I assume the Vout will drop below 12V. As time pass,  4901 will became hotter and finnally trigger its thermal shutdown. After shutdown it will become cooler, and when temp cools to below 150°C, it will work again but still in overload situation if 1A load is still ON. As the cycle goes on, the device will eventually damaged because of overheat. Is this perception correct ? 

2. IF the load current is not constant, sometimes a transient current spike like 1A/5us happens, will 4901 be able to response in time? or how fast (how short the current spike lasts) could 4901 response? 

Thanks!

  • Hi Yi, 

    1. IF during test we intentionally set a large CONSTANT I_load of 1A, we would see the I_out be limited to 309mA(typical) according to section 8.3.1, and I assume the Vout will drop below 12V. As time pass,  4901 will became hotter and finnally trigger its thermal shutdown. After shutdown it will become cooler, and when temp cools to below 150°C, it will work again but still in overload situation if 1A load is still ON. As the cycle goes on, the device will eventually damaged because of overheat. Is this perception correct ? 

    -- Yes, as the current limit kicks in, the LDO can only provide maximum current up to its current limit and the 12V output will be pulled down, the LDO can also cycle in and out from thermal shutdown. Constantly running the device in current limit will reduce the life span of the device and reliability but it will not necessary result in a damage as the life span and reliability are statistical terms. 

    2. IF the load current is not constant, sometimes a transient current spike like 1A/5us happens, will 4901 be able to response in time? or how fast (how short the current spike lasts) could 4901 response?

    --Current limit is a protection feature and it takes time to take control of the pass-FET switch. Normally it may take hundreds of micro-seconds for the current limit loop to start dominating the control loop and limiting the current. The current limit may not respond to a pulse for just 5us. 

    Regards, 
    Jason Song

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