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LDO

Puspam Nayak
Prodigy 140 points
Other Parts Discussed in Thread: TPS7A57, TPS7A85A, TPS7A53A-Q1, TPS7A53-Q1

Hi,

We are looking for LDO with VIN = 4.5 to 10V range, VOUT = 3.3V, IOUT = 3.5 or 4.5 A with Soft Start feature i.e. it should have Soft start Pin 

Regards,

Puspam

  • 0
    TI__Expert 5231 points

    Hi Puspam, 

    Thank you for this question. I have attached an image of our devices that have a soft start pin. We do not have one with a Vin at 10 V. I sent you a range because they are different costs and, in the screenshot, I included the pricing as well so you can pick the best device for your application. Please let me know if you have any further questions. 

    Thank you,

    Josh Nachassi 

     

  • 0 in reply to Josh Nachassi
    TI__Expert 4680 points

    Hello Puspam,

    As mentioned by Josh, we don't have a high current mid-Vin device; however, I would recommend TPS7A57. It is a 5A LDO w/ soft-start pin and it is one of our hero devices!

    Best,

    Eunize Tobias

  • 0 in reply to Eunize Tobias
    Prodigy 140 points

    Thank you Tobia and Josh, can you please suggest 3.3V Fixed part. Adjustable is not taking as an option due to reliability of resistors.

  • 0 in reply to Puspam Nayak
    TI__Expert 4680 points

    Hello Puspam,

    Since 3.3V fixed output is needed, I would recommend TPS7A85A. It has Any-out operation feature which allows adjusting the output voltage without external feedback resistors. In order to get the 3.3V out customer will need to connect pin 6 (100mV), pin 10(800mV) and pin 11(1.6V) to GND since the output voltage is set by the sum of internal Vref (0.8V) plus the accumulated sum of the voltages of the active pins (Vout,nom = 0.8V + 0.1+0.8+1.6 = 3.3V).

    Best,

    Eunize Tobias

  • 0 in reply to Eunize Tobias
    Prodigy 140 points

    Hello  Euzine,

    Thank you for your response. We have evaluated both the part  TPS7A85A and TPS7A53A-Q1

    In my design Steady state current is 1.77A so Power dissipation calculation with VIN = 5V, VOUT = 3.3V/1.7A, 

    Power dissipated (Pd) = (VIN-VOUT)*1.7A = 3.0 Watts

    Ambient temperature (Ta) = 35°C

    So TJ (Junction temperature) = Pd*RθJA + Ta

    For now i am taking RθJA as per datsheet which is 43.4 °C/W 

    So calculated TJ = 3 *43.4 + 35 = 165.2 °C for part TPS7A85A

        calculated TJ = 3 *42.5 + 35 = 162.5 °C for part TPS7A53A-Q1

    Hence TJ is much higher than Max Junction temperature given in both the datasheets which is 150 °C

    Question 1: Can you please suggest copper areas to maintained in PCBA to handle calculated TJ without using heatsink.

    Question 2: With reference to Question 1,  do you have RθJA Vs Copper area calculation required to mitigate thermal issue. Example, given below

    Question 3: In datasheet of TPS7A53A-Q1 why 'Maximum (section 6.1)' and ' Recommended Operating Range (section 6.3)' of TJ (Junction temperature) mentioned same i.e., -40 °C to 150 °C. Can you please clarify?

    Regards,

    Puspam

  • 0 in reply to Puspam Nayak
    TI__Expert 4680 points

    Hello Puspam,

    TPS7A53A-Q1 is a 1.0V fixed output, therefore cannot support the 3.3V output needed. However, we do have TPS7A53-Q1 which is adjustable that could work. The Roja specified on DS is 39.9°C/W on the RTK package as per JEDEC standards. Thermal performance can be improved by 32-55% if PCB design is optimized, more information on this app note: An empirical analysis of the impact of board layout on LDO thermal performance (ti.com). 

    Taking in consideration the DS Roja of 39.9°C/W and Pd =3W (slightly above calculated Pd), the calculated Tj = 35 + (3 *39.9) = 154.7°C.

    Puspam Nayak said:
    Question 1: Can you please suggest copper areas to maintained in PCBA to handle calculated TJ without using heatsink.

    Table 1 on the app note shared above provides descriptions for thermally saturated design layout and copper coverage.

    Puspam Nayak said:
    Question 2: With reference to Question 1,  do you have RθJA Vs Copper area calculation required to mitigate thermal issue. Example, given below

    We don't specifically have for TPS7A85A or TPS7A53-Q1, but we do have this graph for WSON package. Going back to the empirical analysis apps note shared above it has detailed information on how thermal resistance varies with copper area and thickness.

    Puspam Nayak said:
    Question 3: In datasheet of TPS7A53A-Q1 why 'Maximum (section 6.1)' and ' Recommended Operating Range (section 6.3)' of TJ (Junction temperature) mentioned same i.e., -40 °C to 150 °C. Can you please clarify?

    As mentioned above, TPS7A53A-Q1 cannot support 3.3V output since it only has a 1V fixed option. Either way, the absolute maximum ratings table states -55°C to 150°C while the recommended is -40°C to 150°C, which is the same case for TPS7A53-Q1.

    Best,

    Eunize Tobias