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TPS61029-Q1

Mohamed Hellal
Intellectual 2295 points
Other Parts Discussed in Thread: TPS61029

Hello,

I'm working on the power supply for the application, they intend to use the TPS61029 boost converter to provide a 5V power supply for CAN.


Application: TPS61029, Vout = 5V, Vbat = 3.3V

I have some questions about the datasheet http://www.ti.com/lit/ds/symlink/tps61025.pdf :
        - Vout calculation accuracy:

 * 8.5 Electrical characteristics




Is the total accuracy  3% valid for fixed output voltage DC-DC, or is it also valid for adjustable DC-DC?

 For ajustable DC-DC the output votage is calculated with the formula Vout = (R3+R4)/R4*VFB.
 So in my opinion, Vout accuracy depends on the accuracies of:
        -  the TPS61029: specified value 3%??
         - VFB:  specified value 2%
        - the maximum leakage current of the VFB input
        - the resistors R3 and R4: depends on resistors choice

How do we calculate Vout total accuracy for the TPS61029?
- Do we use the formula  Vout = (R3+R4)/R4*VFB taking in account the accuracies of VFB, R3, R4 and VFB leakage current?
- What is the maximum leakage current of the VFB input? (I couldn’t find it on the D/s)
- Do we also take in account the specified total accuracy +-3%?

        - Output capacitor
   
*11.2.2.3 Output Capacitor Selection p16



How do we proceed to define the required ESR?


        - 11.2.3 Application Curves: p.16

Why is the switching frequency 600Hz? Is the true time base 1µs/div instead of 1ms/div? 

Thanks, 

Mohamed

  • 0
    TI__Mastermind 46905 points
    hello
    for the later two questions: an ESR from 30mR to 100mR should be OK; It should be us/div for Fig.14~Fig. 17
    about the output accuracy problem, i may need a few time to provide an answer.
  • 0
    TI__Mastermind 46905 points
    Hello
    about the output voltage accuracy, your understanding is correct. the following four factor impact the VOUT accuracy. so you should sum up them if considering the worst case. but they are independent event, the worst case seem unlike to happen.
    - the TPS61029: specified value 3%??
    - VFB: specified value 2%
    - the maximum leakage current of the VFB input
    - the resistors R3 and R4: depends on resistors choice
  • 0 in reply to Jasper Li
    TI__Intellectual 2295 points
    Hello
    The maximum error acceptable is 5% with 5V regulation, means 5,25Vmax 4,75Vmin.
    R3=18kOhm and R4=2kOhm.

    Can you explain why the power save mode should be disable as the load is not fixed.

    Thks,
    Mohamed