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TPS61291: Regulator Choice for ADS124S08

Wael Hazin
Prodigy 195 points
Part Number: TPS61291

Hello:

We are currently evaluating the ADS124S06IPBS ADC and seem to really like some of its features such as its power consumption. This ADC will be used to measure strain gauge loads and its high precision seems to be ideal. Our product is powered off of a coin cell battery (CR1225) 3V and contains a BLE transceiver. We could use 2 batteries in series if need be. I know its best to use an LDO for a regulator but because of its efficiency and the voltage drop from the coin cell(down to 2.2 volts), This is a far from ideal option for us. Even using 2 batteries in series will yield the same issue. So I have been playing around with the TPS61291 boost regulator and connected it to drive AVSS and AVDD on the ADS124S06IPBS Eval board and did not seem to see much of an increase in noise. I am concerned that I may be missing something during my testing and would like to get your opinion on this matter(in using this boost converter) prior to designing a prototype board. Also, I was not able to find any info in the TPS61291 datasheet with regards to calculating its switching frequency. Should I assume its the LC(output C) resonant frequency assuming I use the recommended L(3.3uH) and C(22uF)? Please note we sell 10s of thousands of these products annually and I need to make sure I am not missing anything. If there is a better choice for our application, please feel free to make a recommendation. In sum, Do you recommend on using this regulator or would you have any other recommendation? Your time and effort will be greatly appreciated.

 

Regards,

WH

  • 0
    Prodigy 195 points
    please note I already posted this question on the data converter forum and was advised to post here.
  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi Wael Hazin:
    It's our pleasure to support.
    May you share some details spec so that I may be able to give you some suggestion. Such as the input voltage range, Vout target, totally load condition. (To be honest, I'm not so familiar with ADS part. We have different team focus on different part.)

    For TPS61291, the Fsw in CCM could be calculated by the current ripple. Details could be seen in "Hysteretic Current Operation" 7.4.1 of the datasheet.
  • 0 in reply to Minqiu Xie
    Prodigy 195 points

    Hello Minqiu:

    Thank you for your reply! the output voltage is 3.3V and the input voltage can be 3 or 6 volts but would prefer to keep it at 3V. the load is minimal, the output continues output current should be around 2 to 3 mA with spikes up to 15 or 20 mA when BLE transmitting. sorry, but I still can not figure out exactly what the switching frequency is. The best I can tell is from Figures 20 and 21 where they show the switching on SW and IL. its a little hard to tell exactly what the frequency is. I need to make sure that this switching frequency is NOT the same as the ADC modulator frequency or a harmonic of it. This ADC frequency is 256k. Again, your time and effort will be greatly appreciated.

    Regards,

  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi WH:
    The calculation is more suitable for CCM. But as you mentioned, it seems the converter will work in burst mode with much lower switch frequency.
    I'll recommend you to apply for an EVM. It's much easier for you to test.
  • 0 in reply to Minqiu Xie
    Prodigy 195 points

    Hi Minqiu:

    What calculations are you talking about? I already have an EVM. please advice on my question regarding how to calculate the switching frequency of this regulator? is there any disadvantage of using this with a delta sigma ADC(ADC124S08)? 

    Thanks

  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi WH:
    As I mentioned before, the calculation is not suitable for Burst mode anymore. So, you could test with the EVM.
    And I'm not expert for ADC well. So I'm not sure if a little voltage ripple will influence it.
  • 0 in reply to Minqiu Xie
    Prodigy 195 points

    Hi Minqui:

    I'm sorry, but I do not understand. Are you saying there is no switching during Burst Mode? if not, then how can you say the calculations do not apply? I'm not even sure what calculations you are talking about. please clarify with specific data and examples.

    Thanks

  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi WH:
    Sorry, I mistake this part with another one. There is no burst mode for TPS61291, my apologies.

    The switching frequency of TPS61291 varied with the input voltage and output current. When the inductor current is discontinue(refer to page 8 of datasheet), the higher output current, the higher switching frequency.

    There is a similar post, you could have a see. e2e.ti.com/.../495244
  • 0 in reply to Minqiu Xie
    Prodigy 195 points

    I understand that it varies and I have read the datasheet and understand how it works. there must be a way/formula to calculate or estimate the frequency based on input current/voltage and output load. I have never seen a switching regulator not talk about the switching frequency. 

    Thanks

  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi Weal:
    I really wish I could give you a equation to calculate the Fsw. Actually, it's to hard to calculate the frequency in this mode precisely. It will be infuenced by too much factors.
    The link I replied last time have a graph about the test result in our lab. It could be a reference.
  • 0 in reply to Minqiu Xie
    Prodigy 195 points

    if this is the link

     e2e.ti.com/.../495244

    your talking about, I get an Access Denied message trying to open it.

  • 0 in reply to Wael Hazin
    TI__Mastermind 21565 points
    Hi Wael Hazin:
    I'm sorry, that an old post.
    I have sent a friendship requirement to you. And you could share your email to me. I'll contact you with email.