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TLV740P: Start-up time

Zeming Kong
Expert 3515 points
Part Number: TLV740P
Other Parts Discussed in Thread: TPS7A20, TLV743P

Hi team,

From datasheet, the start-up time of TLV740P is 100us(typ.), but from Figure 6-25, it shows a about 700ns start-up time.

Could you tell me why the start-up time is different? Is it due to the output current? 

Best,

Zeming

  • 0
    TI__Expert 3515 points

    Sorry, from  Figure 6-25, the start-up time is about 700us .

  • 0 in reply to Zeming Kong
    TI__Genius 12345 points

    Hi Zeming, 

    The conditions in which both start up times are presented are different.

    The typical startup time (typ)=100us is done with a load of 300mA and an output capacitor and considering the following: "Startup time = time from EN assertion to 0.95 × VOUT(NOM)." This means that it takes 100us where EN reaches .95 x VOUT. This is true for an application when EN would be much higher than 1V and up to EN=Vin.

    In Figure 6-25, the testing conditions are different. The load and Cout are open and the EN signal is much lower than Vin and VOUT is much higher than EN as well.

    Assuming VOUT=3.3V then this would mean that the time EN takes to reach 3.135V would be the startup time, however EN~1V which is the minimum voltage to consider EN High. Since EN is on the minimum value, the device will turn on, however, it will never be higher than 3.3V, hence the startup is slower.

    Hope this answers your question. If you have more doubts, please feel free to ask. Have a good one. 

    Best, 

    Edgar Acosta

  • 0 in reply to Edgar Acosta1
    TI__Expert 3515 points

    Hi Edgar,

    Thanks for your explanation.

    Actually, my customer is evaluating 1.8V fixed output LDO, but he needs a >100us soft-start function, TLV740P has a 100us typ. start time, so I was wondering if TPS740P can meet his requirement?

    Best,

    Zeming

  • +1 in reply to Zeming Kong
    TI__Genius 12345 points

    Hi Zeming, 

    Unfortunately TLV740P does not have a soft-start functionality as other LDOs do. Is it possible to know the Vin and Ven signals your customer will implement? 

    If you need larger start up times, I can recommend TPS7A20: 

    tstr=750us and 1150us(max).

    It is a pin-to-pin part and it also comes in a fixed output of 1.8V. 

    Another device that could be used is the TLV743P which is also pin-to-pin:

    I can go into the lab and test TPS740P and try to get a larger startup time if needed. Please let me know if I can help you out with anything else. Have a good one. 

    Best, 

    Edgar Acosta

  • 0 in reply to Edgar Acosta1
    TI__Expert 3515 points

    Hi Edgar,

    Thanks for your advice.

    The customer is connecting input voltage to EN I think, so it should be hard to adjust the start time of TLV740P.

    I will suggest TLV743P and TPS7A20.

    Best,

    Zeming