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LP2985: Lp2985N slew rate requirement for EN

Dilip Namdeo Mohol
Intellectual 1420 points
Part Number: LP2985

There is a special instruction for Von/off pin as below,

 

 

 

 

Please clarify if our understanding is correct:

    1. The regulator shall be definite ON above 1.6V, and definite OFF below 0.5V.Above 1.6V there shall not be a need of slew rate consideration.
    1. After 1.6V, begins the start-up sequence, what is the start up sequence?
    1. To prevent any mis-operation , the slew rate between 0.5V and 1.6V if not 40mV/uS or higher, the state of o/p of regulator shall not change or undefined
    1. The above notes according to website is applicable for 2985N, is this also true for 2985?

 

  • 0
    TI__Genius 10200 points

    Hi,

    Unfortunately, I am not able to see the pictures you linked, but I assume they are the ones shown below:

    Regarding your questions:

    1. This device is ensured to start regulating the output when 1.6 V or higher is applied to the ON/OFF pin. It is ensured to stop regulating when 0.15 V or lower is applied to the ON/OFF pin. 
    2. The start-up sequence refers to enabling the internal blocks of the device. This includes the voltage reference, error amplifier, and protection circuitry. 
    3. If the applied slew rate is less than 40 mV/us, the state of the output will be undefined - it may or may not change. 
    4. Correct, the logic thresholds and slew rate requirements are the same for the LP2985. 

    Thanks,

    Gerard

  • 0 in reply to Gerard Copeland
    TI__Intellectual 1420 points

    Further to this query, we have certain observations with LP2985 which we wanted to discuss. Please see our implementation with LP2985

     

     

    The input to LP2985 is 5V to generate 3.3V o/P. The O/P load cap connected is 10uF ceramic and C bypass is 100nF, ceramic . Please see the nature of I/P wave and O/P generated. We have observed two different O/P behaviors  in the same circuit which we are explained below

     

    Fig 1Behavior 1- Delayed response in 3.3V generation( Device produced Nov 18)                 Fig 2Behavior 2- Fast response in 3.3V generation( Device produced in 2017)

     

     

    The yellow is the I/P waveform of 5V ramping and purple (pink overlaps exactly the purple) is the LP2985 O/P waveform(Please ignore the green and pink one). We see in Fig 1 the O/P is delayed by more than 50mS which may be majorly due to bypass caps. In Fig 2 with same value of bypass , we have seen the O/P generated in almost 15mS.

    Wanted to understand, have there been any changes in tolerances or specification of LP2985, ordering details -LP2985-33DBVR

  • 0 in reply to Dilip Namdeo Mohol
    TI__Genius 10200 points

    Hi Dilip,

    As this question is being discussed via private message I will be closing this thread. If you have any additional questions, feel free to post them at any time.

    Thanks,
    Gerard