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LP3470A: Possible problems for LP3470A with extra capacitance

Masayuki Matsushima
Prodigy 10 points
Part Number: LP3470A
Other Parts Discussed in Thread: LP3470
Hello,

I would like to ask a reset time delay of LP3470A275DBVR.
According to Page 9 in the datasheet of LP3470 series, capacitance of a condenser connected to the SRT port shouldbe up to 10 uF.
However I plan to introduce a condenser with 33 uF for the IC to generate 20 s as a delay time.
I performed an experiment by using a 33 uF condenser, and the result seems successful without any problem.
I would like to know what problems could occur if this IC were continued to use in the same condition.
The datasheet implies in Page 10 that the reset time delay is going to be shortened while the IC switching frequently.
I would like to acquire more information if you have any additional information.

Thank you
  • +1
    TI__Genius 14860 points

    Hi Masayuki-san,

    Thank you for your question. For configurations outside of the specification of the datasheet, we do not have characterization data. For the configuration that you want to implement, capacitance greater than recommended by the datasheet, we tend to see, but not limited to behavior below.

    • Due to higher capacitance, the discharge time also become greater, leading to slower device reaction.
    • Higher capacitor discharge current, which could eventually damage the discharging transistor of the device.
    • The timing equation in the datasheet could become invalid the greater the capacitance is from the max value.

     Jesse 

  • 0 in reply to Jesse Villanueva
    Prodigy 10 points

    Hello Jesse Villanueva,

    Thank you for your thoughtful and beneficial answer.

    My problem has almost solved due to your three hints. My experiment employing LP3470 and 33 uF capacitor also supports the first and third ideas. It seems to be performed with few problems. 

    However, some questions remain about the second idea. I use the IC by applying a voltage of up to 3.6 V to its Vcc port, without its Vcc1 port, and it appears that a current of approximately 2 mA flows into SRT port for a moment. Comparing with recommended conditions of other ports, this current is not extremely large, but I don't make sure the validity of this value.

    I understand difficulties of specifying figures outside the datasheet, but if you can exhibit some comments, I would like to hear them.

    Regards,

    Masayuki Matsushima

  • 0 in reply to Masayuki Matsushima
    TI__Genius 14860 points

    Hi Masayuki-san

    From my second comment, it is hard to say the severity of the possible damage it may cause. Since your capacitor value is not too far off from the datasheet value, the results of the damage may not be observed immediately compared to if you are using a 33mF capacitor for example. 

    Jesse