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TPS7A83A: Application

Ganapathi rao
Intellectual 320 points
Part Number: TPS7A83A
Other Parts Discussed in Thread: TPS7A84A, TPS7A52, TPS7A53, TPS7A53-Q1, TPS7A52-Q1

Hello,

I am using TPS7A83A (For 5V to 3.3V/2A)  by connecting 800mV,100mV,1.6V pins to GND  and similar way for 5V --> 2.5V/2A regulator by connecting  100mV,1.6V pins to GND.

Using TPS7A84A :

For 5V --> 1.2V/3A regulator by connecting  400mV pins to GND.

For 2.5V --> 1.2V/3A regulator by connecting  400mV pins to GND.

Could you please suggest is it okay to use the respective ICs for above applications ?

Thanks & Regards

Ganapathi

  • 0
    TI__Guru 55940 points

    Hi Ganapathi,

    The ANYOUT connections are correct; however, from a thermal perspective you may have issues.  Taking the 5 V to 1.2 V at 3 A rail, we know that 11.4 W would be dissipated in this application.  

    While board layout does have an impact on thermal performance, we can use the Thermal Information Table which is modeled on a JEDEC hi-k board for a first pass at thermal analysis.

    With a Rthetaja of 43.4 C/W this means that at a power dissipation of 11.4 W, the junction temperature will be ~495 C above the ambient temperature.  This is well beyond the 125 C max operating temperature.

    Since your Vout and Iout are set by your load, reducing Vin is going to be the best way to reduce the power dissipation in the LDO.  You can do this by generating an intermediate rail with a DCDC switching regulator to reduce your overall system power consumption, another LDO for high system PSRR, or even power resistors in series with the LDO input.  It should be noted that the last two will simply spread the power dissipation and heat rather than reduce it.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Intellectual 320 points
    Hello Ryan,

    Thanks a lot for your quick response.

    I am generating 5V with a switching regulator on my board as 5V is also needed for other circuits. I have so much constraint on available space on my board. below are actual worst case load currents:
    3.3V --> 0.975A
    1.2V --> 1.56A
    2.5V --> 0.13A

    I am looking for newly introduced ICs, more reliable and less cost/space.
    I am planning to use as below:

    5V to 3.3V: Choosing TPS7A52 or TPS7A83A. Both has equal thermal resistance. As per worst case consumption,operating junction temperature: (5-3.3)*0.975*43.4= 72C
    5V to 2.5V: Choosing TPS7A53 or TPS7A84A oth has equal thermal resistance. As per worst case consumption, operating junction temperature: (5-2.5)*1.69*43.4= 184C. Can we manage with good layout for heat dissipation ?
    2.5V to 1.2V: Choosing TPS7A53 or TPS7A84A oth has equal thermal resistance. As per worst case consumption,operating junction temperature: (2.5-1.2)*1.56*43.4= 87C

    All ICs, has max junction temperature :150C.

    Could you please suggest best option for my application. If i need to use switching regulators for low voltage generation (3.3V/2.5V/1.2V), ii may have space issues on board.

    Thanks & Regards
    Ganapathi
  • 0 in reply to Ganapathi rao
    TI__Guru 55940 points
    Hi Ganapathi,

    Keep in mind that your calculations are estimating how much the junction temperature is above the ambient temperature. As such, you will still need to add in your maximum ambient temperature to estimate the junction temperature.

    It is important to note that TPS7A83A and TPS7A84A are only specified up to a junction temperature of 125 C. TPS7A52-Q1 and TPS7A53-Q1 have an extended junction temperature range up to 150 C. As you are still dissipating a lot of power, the extended temperature range of TPS7A52-Q1 and TPS7A53-Q1 will be beneficial to you.

    The primary heatsink for these LDOs is the GND plane. As such you will want to maximize the GND plane copper connected to the LDOs. With a good thermal board layout (maximizing copper), you could see 20-50% improvement on thermal performance over the JEDEC hi-k board; however, it sounds like you will also have multiple devices dissipating into the GND plane in a small area.

    Adding air flow and additional heatsinking to the devices can further improve thermal performance. If you can find a way to add a thermal resistor in series before the LDO, you will be able to reduce the power dissipating in the LDO.

    Regardless, it is important to keep in mind that you are still dissipating a lot of power in these LDOs. You may need to implement multiple of the above methods to keep the LDOs within their specified operating junction temperature.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Intellectual 320 points
    Hello Ryan,

    Thanks a lot for detailed explanation. As the current ratings are more, i will use switching regulators for 5V-1.2V and 5V-3.3V. I can use LDO for 3.3V-2.5V/0.1A.


    Regards
    Ganapathi