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LM3880: Questions about using the LTM3808

user6236094
Intellectual 310 points
Part Number: LM3880
Other Parts Discussed in Thread: SN74LV244A, , TPS3808
Please tell me the following points about how to use LTM3808.
【Question 1】
 ・Figure 12 in the data sheet shows a circuit example using MOSFETs.
　 Is it possible to directly connect a buffer (such as SN74LV244A) to the / MR pin of the TPS3808G01 and control ON / OFF without using MOSFETs?
　
　
　
【Question 2】
　Is it possible to turn on the VDD and SENSE pins of the TPS3808G01 and release the / MR pin after the power is turned on?
　Is it possible to control as shown in the figure below?
　
【Question 3】
　Please tell me about / RESET Delay Time of TPS3808G01.
　We have a circuit configuration that mounts a capacitor on the CT terminal and uses / RESET Delay Time (td).

　For / RESET Delay Time (td), the following formula was used.

　

　Calculated using CT = 180 [nF] of td (/ RESET Delay Time) in “7.6 Switching Characteristics”,
　but “MIN = 0.7 [s], Typ = 1.2 [s], MAX = 1.7 [s]” There is description, but there is no calculation result.

　Td(s)=CT(nF)/175 + 0.5×10^-3(s) = 180/175 + 0.5×10^-3(s) = 1.02907[s]

　Please tell me how to calculate MIN = 0.7 [s], Typ = 1.2 [s], MAX = 1.7 [s].

  • 0
    TI__Guru 60800 points

    Hello

    This is question for TPS3808 instead of LM3880. TPS3808 team will address for you.

    Regards

    Yihe

  • 0 in reply to yihe
    TI__Genius 9375 points

    Hi user,

    Here are my responses for your question:

    1. You can connect a buffer to control /MR as long as you are driving logic low and high and holding these signals to control the output.l

    2. Yes, you can control the /MR with a GPIO or a switch.

    3. The /RESET time delay here differs a little bit as a result of the data in the table coming from experimentation that has many variables (cap tolerance, type of cap) and the equation coming from a design perspective. I would recommend using the equation to design around your desired delay time and re-checking to see if it resulted in what you intended.

    Thanks,

    Abhinav.