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UCC24624: Supply voltage vs internal clamp diode

Michiaki Tanii
Expert 4610 points
Part Number: UCC24624

Hi team,

 

Please let me make sure the internal clamp diode for VDD.

 

VDD_CLAMP is specified between min 24.75V and max 29.5V at IVDD = 15 mA but VVDD is specified MAX 26V as recommended operating conditions and 28V as absolute maximum ratings.

How should we think on this ?

Customer should use up to 26V for VVDD ?

 

Thank you and best regards,

Michiaki

  • 0
    TI__Guru 74115 points

    Customer should use the recommended operating conditions, so VVDD should be between 4.25V and 26V.

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    In your answer, the application described in the datasheet at 13 page such as below could not be applied.

    Is my understanding correct ?

     

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    The recommended is between 4.5V and 26V when internal clamping is not triggered or triggered but with the current <= 15mA. If you have voltage that can trigger clamping with current > 15mA, you need to add current limit resistor.

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    Hi Hong,

     

    If customer should keep between 4.6V and 26V as you mentioned, the application I attached in previous post is needed the regulated voltage up to 26V for VDD even if the current for VDD was less than 15mA.

     

    I think that it is not consistency between the application example and electrical characteristics customer should follow.

     

    Please let me double check again.

    If customer should follow what you mentioned, VDD should be supplied regulated voltage and customer couldn’t consider the application such as figure 15.

     

    I would much appreciate I got your any comments.

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    The recommended table should be followed. If the external bias can be > 26V, then a current limit resistor should be added along with your expectation how high the VDD can reach. 

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    Hi Hong,

     

    Could you kindly advise how to determine the appropriate value for current limit resister ?

    How could customer follow the datasheet if supply voltage was more than recommendation such as figure 15 ?

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    The recommended operation table suggests you design within the table specified range. Figure 15 suggests if VDD is higher than the recommended range listed in the table. If the VDD in your design <= 26V, add a current limit resistor is not a must. when you need to add a resistor, the resistor value can be determined in the way of recommendation along with Figure 15 to setup VDD = 24.75V, or you can calculate the resistor value with VDD = 26V. The device can work either way. But the power losses will be different. The Figure 15 gives design with some margin to reduce power losses.   

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    Hi Hong,

     

    Please let me make sure the supply voltage in the case of over 26V for supply voltage.

     

    In your explanation, if supply voltage is over 26V, customer can use UCC24624 by adding a series resister by less than 15mA for input current of VVDD.

    In the datasheet, maximum VDD clamp voltage is 29.5V and the voltage is larger than 26V for supply voltage in the recommended operating conditions.

     

    I feel it is inconsistency.

     

    But if customer follow the application such as fig15, customer can use UCC24624 even if VVDD is over 26V of recommended operating conditions by internal clamp diode.

     

    Is my understanding correct ?

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    The minimum clamping is 24.75V, with this minimum clamping, if applying 26V on to VDD without external current limit resistor, the IC is still ok. But you cannot assume every IC has clamping voltage 29.5V, and you have to think about the worst case as 24.75V. That is why you need to add current limit resistor when VDD > 26V since the IC can have clamping between 24.75 and 29.5V and you do not know which one has 24.75 and which one has 29.5V so you need treat for the worst case. But if you know the VDD not > 26V, it is your option to add or not to add the current limit resistor, either way, the IC will be safe to operate but may show different power losses.

     

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    Could you kindly share the characteristic of internal clamp diode ?

    In the use case of customer, output voltage is 24V, so customer will add the series resistor considering the transient response and the protection.
    Since customer should treat for the worst case and follow the recommended operating conditions, they should estimate the clamping voltage by adding the series resister but we couldn’t find the characteristic of internal clamp diode.

    Thank you and best regards,
    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    After you decide your worst case voltage, you can just select the resistor value to limit the current < 15mA using either 24.75V clamping or 26V clamping. I do not see what else you need for your design on the internal Zener.

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    How can customer follow the recommended operating conditions for supply if customer add the current limit resister to VDD ?

    Even if customer regulate that IVDD is less than 15mA, VDD might be over than recommended operating conditions because maximum VDD clamp voltage is specified at max 29.5V and the number is over than recommended operating condition.

     

    I think customer should be regulate IVDD is much less than 15mA. For instance between 5mA and 10mA ?

    If you couldn’t share the characteristic of internal clamp diode, please give us your recommendation number of IVDD not to over the recommended operation conditions max 26V.

     

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    If you know VDD maximum is 26V, and typical is 24V, no need to add the current limit resistor.

    If your output voltage = 24V, the internal Zener does not conduct, the current will be < 15mA, no matter the Zener clamping voltage is 24.75V or 29.5V.

    If your output voltage = 26V, and the internal Zener clamping between 26V and 29.5V, the internal Zener does not conduct, the current < 15mA.

    If your output voltage = 26V, and the internal Zener clamping is 24.75V, then the current is 15mA from internal Zener characteristics.

    So no need to add the resistor if your max VDD is 26V.

    If your VDD max is > 26V, please provide the max VDD, I can provide the resistor value for you.

     

  • 0 in reply to Hong Huang
    TI__Expert 4610 points

    Hi

    Max VDD will be 30.69V.

    Please provide the recommended resistor value.

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Expert 4610 points

    Hi

    Sorry for pushing you but could you kindly advise the recommended resister value.

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 74115 points

    Resistor value 332-ohm can be used.