• State Resolved
  • Locked Locked
  • Replies 17 replies
  • Answers 7 answers
  • Subscribers 63 subscribers
  • Views 546 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPS22976： application issues

Aaron Hsu
Intellectual 565 points
Part Number: TPS22976
Other Parts Discussed in Thread: TPS25982

Dera sir

1.When TPS22976 is applied to VIN capacitor <VOUT capacitor, do I need to worry about damage to TPS22976?

   VIN capacito(88uF~120uF)  < VOUT capacitor(200u~470u)  

2.Do I need to follow the datasheet Reverse Current Blocking Figure 10-4 in the application where the IN capacitance is less than the OUT capacitance to avoid current passing through the body diode to damage the TPS22976?

3.Is there a Thermal Shutdown Plot During Start-up Figure available for TPS22976?    Such as TPS25982 datasheet Figure 53

  • 0
    TI__Genius 10652 points

    Nice to speak with you again Aaron :)

    Aaron Hsu32 said:

    1.When TPS22976 is applied to VIN capacitor <VOUT capacitor, do I need to worry about damage to TPS22976?

       VIN capacito(88uF~120uF)  < VOUT capacitor(200u~470u)  

    There is no potential for damage in such a condition. There may be a slight current peak on VIN as the load is released. 

    Aaron Hsu32 said:

    2.Do I need to follow the datasheet Reverse Current Blocking Figure 10-4 in the application where the IN capacitance is less than the OUT capacitance to avoid current passing through the body diode to damage the TPS22976?

    There wont be potential for body diode conduction unless your VOUT get supplied by a higher voltage source after turning the device on, which is not done exactly because it will reverse conudction thru body diode. 

    You shouldn't need to configure the device for RCB unless you will supply VOUT with a voltage > VIN above the forward voltage of body diode. 

    Aaron Hsu32 said:

    3.Is there a Thermal Shutdown Plot During Start-up Figure available for TPS22976?    Such as TPS25982 datasheet Figure 53

    We do not have such a plot available for TPS22976
    Please let me know if any other questions, if this answers all your questions, please let me know by pressing the green button. 
    Best
    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    Dear James
    There is no potential for damage in such a condition. There may be a slight current peak on VIN as the load is released.

    =>1.In our application, the TPS22976 VOUT may be unloaded. When the VIN terminal DC-DC is powered down, the TPS22976 EN PIN will also be pulled LOW. Will TPS22976 be damaged? VIN capacito(88uF~120uF) <VOUT capacitor(200u~470u )

    We do not have such a plot available for TPS22976

    =>How do we make sure that TPS22976 will not exceed the power of TPS22976 during VOUT Rise?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron, 

    IS VOUT supplied by another voltage source after VIN goes offline?

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    IS VOUT supplied by another voltage source after VIN goes offline?

    =>NO , VOUT no other source

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    If this is the case, then there shouldn't be an issue with reverse conduction that needs to be addressed in hardware. 

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    1.Our application is that the VIN of TPS22976 is supplied by DC-DC. When DC-DC is powered down, TPS22976 EN PIN will be pulled LOW, so Reverse Current Blocking is required?  As attached

    VIN capacito(88uF~120uF)  < VOUT capacitor(200u~470u)  

    TPS22976.docx

    2.How do we make sure that TPS22976 will not exceed the power of TPS22976 during VOUT Rise?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron, 

    You shouldn't need to worry about a reverse conduction in this case. 

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    1.You shouldn't need to worry about a reverse conduction in this case. 

    =>Thanks for answering

    2.How do we make sure that TPS22976 will not exceed the power of TPS22976 during VOUT Rise?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron, 

    you can estimate based on ambient temperature experienced by the system, and add the power thru the body diode (I*V) multipled by Rj_theta_a. Note that we do not have IV characteristic for the body diode so it may require bench testing to get the most accurate result. 

    Junction temperature should be calcualted to be below limits. A reminder that the TPS22976 body diode is not recommend to do continuous reverse conduction.

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    How to make sure that the power consumption of TPS22976 will not exceed TPS22976 during startup?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron, 

    What startup conditions are you concerned about? Could you please elaborate?

    The power estimation is used to ensure junction temperature will not exceed maximum and the equation is roughly the same for all. 

    This roughly assumes steady state conditions as you want to know the average power over the entire operation time.

    Startup conditions are very short duration and not steady-state conditions, so you shouldn't need to worry about exceeding power limit.

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    conditions 

    VIN1  5V  、 VOUT1  5V 、  CT1=1000p     rise time 1.768ms     COUT =220u~470u

    VIN2   3.3V 、VOUT2  3.3V 、CT2=1000P  rise time 1.22ms       COUT=150u~470u

    Why do some parts need to pay attention to PD (STARTUP), such as TPS25982, TPS22976 do not need to pay attention, the essence of the part is not a MOSFET?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron,

    there seems to be a problem with this thread, i had previously seen your Dec8 response but now it is nowhere to be found. 

    I remember your question though, i will response it here:

    Yes you do care about the startup power, but we specifically choose CT cap to change the rise time. Charge delivered to the caps remains the same, so we lengthen the rise time to reduce the inrush current and spread the charging over time. This can be adjusted even after board layout by modifying cap value.

    3.3V , 470uF Cout max, Rise time: 1.22ms

    I am watching a presentation for TI tech day now and my colleague summarized the considerations extremely well just as i was typing this, here is a cap from his slide which has the equations. This is not exclusive to HSS, exactly same for load switch .

    For your system, the inrush current soaked by the caps during initial charging is ~1.27A, which is easily be under the power limit for the device unless your load current pulls a ridiculous amount of current at startup.

    Please let me know if any additional questions on this topic, 

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    I understand that Inrush Current = C × dV/dt

    PD(STARTUP) = PD(INRUSH)+PD(LOAD)

    Some parts provide Thermal Shutdown Plot During Start-up, but TPS22976 does not
    I still don’t know how much power the TPS22976 can be rated when STARTUP

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    Aaron,

    We don't have published power limit, The steady-state power limit depends on ambient temperature and average load condition. As long as the Tj<125C, and MAX conditions for voltage, current are not exceeded it is acceptable operation area. 

    The abs max condition for IV are in this section (copied below), thermal power calculation.

    During startup, the device does controlled rise time according to CT cap, and your rise time is set at 1.2ms roughly, ~1.27A as we calcualted above.

    Because this time is so short, calculating the Tj in the manner of Section 12.3 is not valid because it happens for short duration. 

    My recommendation is simply to ensure V/I max conditions are not exceeded at startup, and to ensure that Tj is <125C steady state (average load current)

    Best

    Dimitri

  • 0 in reply to dimitri james
    Intellectual 565 points

    HI James

    My recommendation is simply to ensure V/I max conditions are not exceeded at startup

    =>Just confirm that VIN is below 6V 、Inrush Current+ILOAD Current is below 6A Is it ok?

  • 0 in reply to Aaron Hsu
    TI__Genius 10652 points

    As long as this condition is not experienced regularly (only at startup) then yes.

    Best

    Dimitri