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TPS709: INPUT: 5~17V@50mA / OUTPUT : 3.3V/100mA

Inho Jeon
Expert 1452 points
Part Number: TPS709
Other Parts Discussed in Thread: TPS62203, TPS62172

Hi All,

I'd like to design INPUT: 5~17V@50mA  / OUTPUT : 3.3V/100mA using TPS709.

Is it correct way? 

Applied Device is vibration motor for wearable device. 

Please, Reply me , ASAP.

Best Regards,
Inho Jeon.

  • 0
    TI__Guru 50090 points

    Hi Inho Jeon,

    Just a clarification, an LDO does not increase the input current. So IIN=IOUT+IQ.

    That being said, the primary concern would be thermal performance. If your nominal VIN is 5V and nominal VOUT is 3.3V, then at 100mA, your power dissipation is (5-3.3)*0.1 or 170mW of power. We have two packages available for the TPS709 SOT23 and 2x2 SON. The thermal performance of these two packages are very different. The SOT-23 has a TJA of 212.2C/W and the 2x2SON has a TJA of 73.1C/W.

    What this means is that with the SOT-23 package your temperature rise would be 170mW*212.2C/W or ~36C above ambient. For the 2x2SON package this would be only ~12.4C.

    If VIN is 17V with 3.3V at the output and 100mA for the load, then thermally this becomes difficult for both packages as (17-3.3)*0.1= 1.37W! So with the 2x2SON package your thermal rise would be 1.37W*73.1C/W=~100C above ambient!  This is right at our recommended operating maximum temperature of 125C. The SOT-23 package  would thermally shutdown in this scenario.

    I hope this answers your question.

    Regards,

  • 0 in reply to JCHK
    Expert 1452 points
    Dear John,

    Thank you for your reply.

    And, Is it possible for that case(IN: 5V@50mA/3.3V@100mA) using DC/DC Converter of Ti?

    Please, Request your part suitable my conditions, ASAP.

    Best Regards,
    Inho Jeon.
  • 0 in reply to Inho Jeon
    TI__Guru 50090 points

    Hi Inho Jeon,

    I am sorry but unfortunately the answer is no. The scenario you have is 5V at 50mA is an Input power of 250mW. If you had a 100% efficient DC/DC you could get 100mA at 2.5V (2.5V*0.1A=250mW). For 3.3V at 100mA you would be providing 330mW to the load. It is not possible to derive this from an 250mW input power.

    The best you can get might be with the TPS62203 which has an efficiency of ~95% from 5VIN to 3.3VOUT at 100mA. This would require at least 70mA of current from 5V. For additional questions on DC/DC converters, please post on the DC/DC forum.

    Regards,

  • 0 in reply to JCHK
    Expert 1452 points
    Dear John,

    Thank you for your reply quickly.

    You mean "input : 7V@50mA" is proper that my condition(output 3.3V@100mA), Is that right?
    (Cause, my power source is 50mA fixed but Voltage level is up to 17V.)

    And, Please, Request your part suitable my conditions, ASAP.(Cause, TPS62203 is input level 6Vmax)

    Best Regards,
    Inho Jeon.
  • 0 in reply to Inho Jeon
    TI__Guru 50090 points
    HI Inho Jeon,

    Yes a 7V input DC/DC with 95% efficiency to 3.3V at 100mA should limit the input current to around 50mA (no design margin). For the best recommendation on DC/DC, In am moving this to the DC/DC forum so you can get a better recommendation

    Regards,
  • 0 in reply to JCHK
    TI__Guru**** 150770 points
    The TPS62172 is likely the smallest 17Vin solution.