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TPS7A4701-EP: regarding Calculatio of softstart

Maharajan P
Intellectual 255 points
Part Number: TPS7A4701-EP
Other Parts Discussed in Thread: TPS7A57,

Tool/software:

Dear Team,

TPS7A4701-EP

For the above mentioned part


to determine the softstart,The terms are given without any units in datasheets, Please refer the attached image
Please Guide me with determining the softstarts for 

The input Output voltages and Currents and are given below

Part Number TPS7A57 TPS7A57
Selected Regulator Type LDO Regulator LDO Regulator
Selected Regulator's Maximum output current (A) 1 1
Typical Output Voltage of Selected Regulator - Vo (V) 1.8 3
Planned Input Voltage of Regulator - Vi (V) 3.3 5
Required Output Current of Regulator - Io (A) 0.4068 0.8592
Calculated Input Current of Regulator - Ii (A) 0.407 0.859
Soft start time Tss (ms) ? ?

Conider Cnr/ss to be 1uF or the best value you suggest , I need Rise time around 1ms to 2ms
Please help me with filling the Tss, or the Cnr/ss

Thanks and regards, 
Maharajan P 

  • 0
    TI__Expert 4125 points

    Hello Maharajan,

    It looks like the picture did not upload correctly. Can you please upload it again?

    Also, do you need to calculate the soft start on the TPS7A57 or the TPS7A4701-EP?

    Best regards,

    Daniel

  • 0 in reply to Daniel Esparza
    Intellectual 255 points

    Hii Daniel,
    Sorry for the confusion, 
    Need to be Calculated for Both TPS7A4701-EP. and TPS7A57 I will add the Detailed and correct table column below

    Part Number TPS7A4701-EP TPS7A4701-EP TPS7A57
    Selected Regulator Type LDO Regulator LDO Regulator LDO Regulator
    Selected Regulator's Maximum output current (A) 1 1 5
    Typical Output Voltage of Selected Regulator - Vo (V) 1.8 3 0.925
    Planned Input Voltage of Regulator - Vi (V) 3.3 5 1.2
    Required Output Current of Regulator - Io (A) 0.4068 0.8592 3.9684
    Calculated Input Current of Regulator - Ii (A) 0.407 0.859 3.9684
    Soft start time Tss (ms) ? ?  ?

    Please Respond as soon as possible, 

    Tanks and regards, 
    Maharajan P

  • 0 in reply to Maharajan P
    TI__Expert 4125 points

    Hello Maharajan,

    Thank you for the clarification. I will reply with the calculations within a business day.

    Best regards,

    Daniel

  • 0 in reply to Daniel Esparza
    Intellectual 255 points

    Hi Daniel, 

    Thank you, and please speedup an respond as soon as possible.

    Thanks and regards, 
    Maharajan P

  • +1 in reply to Maharajan P
    TI__Expert 4125 points

    Hello Maharajan,

    To calculate the soft start time of the TPS7A57, please refer to equation 3 on page 57 in the datasheet (https://www.ti.com/lit/ds/symlink/tps7a57.pdf): 

    • Soft-start time (Tss) = (VOUT(target) × CNRss) / ( ISS)
      • Tss = 0.001 (1ms)
      • ISS = .0002 (200uA)
      • VOUT(target) = 0.925
         
      • For a 1 ms start time:
      • CNRss = (.0002 * 0.001) / (0.925); CNRss = 216nF

     

    To calculate the soft start time of the TPS7A4701-EP, please refer to equation 5 on page 16 in the datasheet (https://www.ti.com/lit/ds/symlink/tps7a4701-ep.pdf): 

    •  Tss = 100,000 * CNR * Ln((Vr + 5)/5)
      • Tss = 0.001 (1ms)
      • Vr = 1.4V
         
      • For a 1ms start time:
      • CNR = (0.001)/(100,000*Ln(1.28)); CNR = 40.5nF

    Part Number

    TPS7A4701-EP

    TPS7A4701-EP

    TPS7A57

    Selected Regulator Type

    LDO Regulator

    LDO Regulator

    LDO Regulator

    Selected Regulator's Maximum output current (A)

    1

    1

    5

    Typical Output Voltage of Selected Regulator - Vo (V)

    1.8

    3

    0.925

    Planned Input Voltage of Regulator - Vi (V)

    3.3

    5

    1.2

    Required Output Current of Regulator - Io (A)

    0.4068

    0.8592

    3.9684

    Calculated Input Current of Regulator - Ii (A)

    0.407

    0.859

    3.9684

    CNRss

    		 40.5nF 40.5nF

    216nF

    Soft start time Tss (ms)

    1ms

    1ms

    1ms

     

     For additional details on startup, please consult the following technical white paper:

    https://www.ti.com/lit/wp/slvafx0/slvafx0.pdf

     Best regards,

    Daniel

  • 0 in reply to Daniel Esparza
    Intellectual 255 points

    Hi Daniel, 

    Thank you for the reply, 

    It was very Helpful,

    Regards, Maharajan P

  • 0 in reply to Maharajan P
    TI__Expert 4125 points

    Hello Maharajan,

    You are welcome. I am closing this thread.

    Regards,

    Daniel