• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Subscribers 62 subscribers
  • Views 985 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.

TPS24700/24701 Questions

Byoungkil Jung
Prodigy 160 points
Other Parts Discussed in Thread: TPS24700, TPS24701

Hi, I'm Byoungkil Jung from Korea.

I'm sorry because I have a poor english ability.

I have a plan to use Hot-swap controller, TPS24700 or TPS24701.

But I have some questions about this ICs.

 

TPS24700 is Latch off type and TPS24701 is Auto retry type.

As seeing the Fig28 & 29, at the overload condition, two types are operating differntly..

but I didn't understand exactly between two types.

I have been understand as follows;

Using the TPS24700,

at the overload condition Timer starts.

and after ending overload condition, TPS24700 IC turns on?

Using the TPS24701,

at the overload condition Timer starts.

and after 16 Timer cycles, if PGb is low, TPS24701 IC turns on?

 

Plese explain the Operation of two types at the overload condition.

 

  • 0
    TI__Genius 12380 points

    Hi Byoungkil,

     

    The IC turns the gate on after the enable signal is high and a turn on delay passes. Then the gate will stay on until one of the following conditions occur:

     

    Latch Off: 

     

    At an overload condition, the device will start the timer. If the overload does not go away within the timer period, then the device will shut off the gate of the MOSFET and remain off until the EN pin is toggled.

     

    Auto Retry:

    At an overload condition, the device will start the timer. If the overload does not go away within the timer period, then the device will shut off the gate. Then the device will cycle the timer on and off 16 times (this allows a controlled period of shutoff time so that the MOSFET can cool down) and will then attempt to turn on the gate. It will keep doing this but since the duty cycle is effectively 1/16, the MOSFET may be able to handle this stress for extended periods of time (depending on the MOSFET).

     

    The choice ultimately depends on the application, whether the device should stay off in an overload condition, or attempt to try again.

     

    Also, to help with your design, we have a Design Calculator Tool available on the product folder under "Tools and Software"

    http://www.ti.com/product/TPS24700/toolssoftware

    Feel free to use this tool to design a great circuit! 

    Thanks!

    Alex

  • 0 in reply to Alex Triano
    Prodigy 160 points

    Hi, Alex.

    Thank you for your answer.

    By the way, I have more questions.

     

    (1) I have a plan to use LED for PGb-pin.

    In TPS24700EVM document, there is a TR for PGb LED.

    But I want to use Buffer IC. Is this possible?

    If possible, please recommend the Buffer IC.

    This Buffer will be used Only for PGb-LED.

     

     (2) In the TPS24700/1 Datasheet,

    there is a Gate output voltage for VCC=12V.

    If  Vcc=5V, Gate output voltage is same to that for Vcc=12V?

    (3) About Timer pin operation condition,

    As I understand, Timer operated as follow conditions;

     - Initial start-up sequence

     - Overload situation

     - short-circuit condition

    Is this right?

    there are so many questions,

     

    Regards,

    Byoungkil. 

     

  • 0 in reply to Byoungkil Jung
    TI__Genius 12380 points

    Hi Byoungkil,

    1. We would recommend using the circuit in the EVM.

     

    2. See Figure 11 in the Datasheet, Page 9. Gate voltage would be roughly 17V at Vin = 5V.

     

    3. Yes you are correct. You can always check by reading page 16 of the datasheet, "PGb and Timer Operations"

     

    Thanks!

    Alex

  • 0 in reply to Alex Triano
    Prodigy 160 points

    Hi Alex.

    Thank you for your advice.

     It is very useful to me.

    But I have more questions about diodes(D1, D3, D6) in EVM-document.

     

    (1) D1, TVS Diode.

    As I Know, TVS-diode is used to protect impulse voltage for input side.

    Becuase this impulse voltage occurs at the insertion/removal of hotswap card,

    use of TVS-diode is good at hotswap application.

    Is this right?

     

    (2) D3, Schottky Diode

    As I Know, schottky diode is used to protect from negative voltage transient.

    and it has shorter reverse-recovery time than that of general diode.

    Maybe

     

    (3) D6, Zenner Diode

    Zenner diode is used for regulating the voltage.

    Our system main Vcc is 5V, then V_GATE is about 20V (see datasheet Figure 11).

    If I want to set the  V_GATE is 10V, selection of  50V zenner diode is proper selection?

     

    there are very many questions, but maybe this post seems to be last question.

     

    regards.

    Byoungkil.

  • 0 in reply to Byoungkil Jung
    TI__Genius 12380 points

    D1 protects Input, D3 protects output (see OVP on page 4 of EVM user guide), D6 protects Vgs.

     

    For information on TVS selection, we have the following article:

    http://powerelectronics.com/power_semiconductors/circuit_protection_ics/tvs-clamping-hot-swap-circuits-0911/index.html

     

    For D6, is there a reason you want to set Vgs to 5V?

    For many MOSFETs, a 10V-12V Vgs or higher is needed for full enhancement and thus the gate voltage for the TPS24700 was designed and rated for 30V.

     

    At 5V, V_GATE would be roughly 17.5V accoring to Figure 11 in the datasheet.

     

    If you wish to clamp the gate voltage smaller, you may do so. See page 21 of the datasheet for information about Gate Clamp Diodes. A zener of 5V would accomplish a 5V Vgs and thus is Vcc is 5V, V_GATE would be ~10V.

     

  • 0 in reply to Alex Triano
    Prodigy 160 points

    Thanks, Alex.

     

    I understand that

     (1) D6 is Gate voltage clamp diode  

     (2) R19-C9 connection protect at overstress and abnormal condition.

    Anyway two methods are gate protection circuit.

     

    When CISS of MOSFET is less than 3000pF, method(2) is recommened from TI.

    When CISS>4000pF, method (1) is recommened from TI. 

     

    When I use 8.2V-zener for D6, then V_gate-source is clamped about 8.2V from V_GATE - Vout >8.2V.

    Are these right?

     

    I'm sorry about that I have so many question post.

     

    Thanks,

    Byoungkil.

     

  • 0 in reply to Byoungkil Jung
    TI__Genius 12380 points

    Hi Byoungkil,

    Do not be sorry, we are glad to help our customers :)

     

    You can trust the datasheet which I am guessing is where you are finding this information (page 22).

     

    R19 and C9 form an RC circuit which we use the terms "Soft Start" (SS) or "dV/dT control". This effectively slews the output voltage. It does this since I = C dv/dt.  If I = the gate sourcing current, C = the soft start capacitor, and dv/dt would be the slew rate.

    Since V gate ~ = Vout + Vgs, dv/dt of the gate = dv/dt of Vout. Therefore, by setting the capacitor (C9) in the diagram, you can control the output voltage slew rate. R19 should be at least 1k in order to protect the GATE pin from sinking too much current when the gate pulls low and C9 must drain.

     

    D6 protects the Vgs and is recommended when using SS and CISS is greater than 4000pF.

     

    Thanks!

    Alex

  • 0 in reply to Alex Triano
    Prodigy 160 points

    Hello Alex,

     

    You missed this question.

     

    When I use 8.2V-zener for D6, then V_gate-source is clamped about 8.2V from V_GATE - Vout >8.2V.

    Are these right?

    In EVM-documnet,  TVS-diode is used to protect input-side, schottky-diode is used to protect output-side.

    I wanna know why use a TVS on the input side is, why use schottky on the output-side is?

    Is using the TVS-diode(or schottky) on both input and output side incorrect??

    I'm the begginer on this engineering, Please reply these question.

     

    Regards,

    Byoungkil.

  • 0 in reply to Byoungkil Jung
    TI__Genius 12380 points

    Hi Byoungkil,

     

    Yes, if you use a 8.2V zener across Vgs of the MOSFET, then this will allow a path of current to flow which will limit the Vgs (V_gate - Vout) to ~8.2V.

     

    During a circuit breaker condition, the MOSFET will turn off and the input voltage will spike high and must dissipate a large amount of power, thus requiring a TVS. See the following article:

    http://powerelectronics.com/circuit-protection-ics/tvs-clamping-hot-swap-circuits

     

    For the output, it will also experience high currents and parasitic inductances but instead protection is needed to prevent Vout from going below GND. Because of this, a high power schottky diode is needed on the output to prevent Vout from going below its absmax of -0.3V .

    This is briefly mentioned on page 6) of the datasheet under the "OUT" description as well as page 21) of the datasheet under "Output Clamp Diode".

     

    Thanks!

    Alex