• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 276 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS24770: Using Soft Start - IHGATE and TINR Considerations

Naizeng Wang
Expert 3745 points
Part Number: TPS24770

Hi team, 

I am so confused about the 9.3.6 section in datasheet. So there are 3 questions. 

(1) Can TPS24770 achieve soft start itself? Or it must be achieved by external circuit? There is no detailed explanation of the soft start circuit.

(2) There is a 55uA current source in TPS24770. According to Figure 15, will this current change as the change of Vimon is there are no external soft start circuit?

If the 55uA is fixed, what does figure 15 mean? 

(3) "As an example consider the usage case where the maximum inrush current (IINR,MAX) is 2A". I think the max inrush current happens at the minimum Vds. But following formula uses the max Vds, that is Vin,max. Why? 

As the decrease of Vds, the inrush current will become larger and larger and finally exceed 2A. 

 

Br,

Naizeng Wang.

  • 0
    TI__Mastermind 29715 points

    Hi Naizeng,

    Thanks for reaching out to us. We will get back to you by tomorrow end of the day. 

  • +1
    TI__Mastermind 29715 points

    Hi Naizeng,

    Please see the answers to your quires.

    1) Soft Start (DVDT startup) can be achieved by incorporating a series combination of capacitor and resistor at HGATE pin to GND as shown below. 

    Please refer to the Section 3.2.2.7 (Choosing the VOUT Slew Rate) of Robust Hot Swap Design App Note for detail design procedure.

    2) IHGATE will change with VIMON when the Hot Swap controller is in power limit and VHGATE is Changing. IHGATE will become 55µA only after the completion of inrush mode to enhance the gate of MOSFETs to the maximum gate voltage as mentioned in Electrical Characteristics of TPS2477x datasheet. Please see the following waveforms obtained from the simulation.

    3) In case of DVDT Startup, inrush current (IINRUSH) will be fixed at a specified value based on COUT and rising slew rate of VOUT. In fact IINRUSH is the product of COUT and rising slew rate of VOUT. During DVDT Startup, rising slew rate of VOUT is constant. Current flowing through the MOSFETs will be minimum during power limit at maximum value of input voltage. There is a minimum value of voltage drop across the RSENSE to ensure reasonable accuracy of the power limit engine. Hence, minimum value of power limit should be calculated based on maximum input voltage not the minimum one. Please see the application section of TPS2477x datasheet for detail explanation.