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TPS736: Question about load regulation of TPS736

Masayoshi Takahashi
Intellectual 1530 points
Part Number: TPS736

Hi team,

I have some question of TPS73601 as below. Especially, load regulation.

1. VFB is 1.198 to 1.21V at Tj = 25 deg. How much the VFB during Tj = -40 to 125 deg? I think 1%.

2. Unit of Load regulation mentioned %/mA. How to define this? For example, if Iout=100mA and Vout is setting 1.23V, ⊿Vout=0.05%. So, the worst case is Vout = 1.23 x (1-0.05%) = 1.218V. Is it correct?

3. How much the ⊿Vout(⊿Iout) load regulation during -40 to 125 deg?

4. Below table 6.5 and figure 1 looks like different. Which is the trust value?

Could you please give me your advice?

Regards,

Yoshi

  • 0
    TI__Prodigy 515 points
    1 When evaluating if a device has the right accuracy spec for your application it is better to evaluate the accuracy of Vout rather than Vfb. While Vfb is used to calculate the resistor divider for a specific output voltage, there are other potential sources of error (such as the error amplifier) which means the Vfb spec does not give a complete picture when it comes to output accuracy. The accuracy of the Vout is the key parameter, other than the VFB, over the operating temperature range. The internal feedback loop circuitry does compensate the variations of VFB due to temperature to ensure the Vout maintain 1% of accuracy from -40 to 125 degC.

    2 Load regulation is defined as the ratio of output voltage change to the load current change. %/mA is the percentage of ∆Vout per 1mA load current change. If Iout=100mA, Vout is setting 1.23V, when the load current is changed to 200mA, the change of Vout is going to (0.0005%*1.23)*(200mA-100mA)=0.000615V , which is very small. It measures the LDO’s ability to maintain the constant output voltage under varying load condition.

    3 ⊿Vout(⊿Iout) values calculated for both -40C and 125C using the load regulation chart (figure 1 ) is well within the typical spec at 25C. It is practical to use 0.002%/mA and 0.0005%/mA, typical number in the load regulation spec, to estimate the ⊿Vout(⊿Iout) over the operating temperature range. Char graphs are usually averages of ~30units which show the typical performance of devices and don’t imply any sort of min/max.

    For 1 mA ≤ IOUT ≤ 400 mA, typical ⊿Vout(⊿Iout) = 0.002%/mA * Vout
    For 10 mA ≤ IOUT ≤ 400 mA, typical ⊿Vout(⊿Iout) = 0.0005%/mA * Vout

    4. To get the load regulation data from the graph, divide the data in y axis (Change in Vout(%) ) by the change of the current( Iout in x-axis – Iref (10mA))
    For example, for Iout = 350mA, Vout(%) = -0.8% , the load regulation = Vout(%)/(Iout-10mA) = -0.08%/(350-10) = 0.0002%/mA. The value calculated from the graph meets the spec.
  • 0
    TI__Intellectual 1530 points
    Hi Min,
    Thanks for your quick reply.

    I'd like to confirm the question regarding #3 and #4.

    #3 Datasheet mentioned "Typical values are at Tj=25C".
    Below value is at -40 C to 125C?
    For 1 mA ≤ IOUT ≤ 400 mA, typical ⊿Vout(⊿Iout) = 0.002%/mA * Vout
    For 10 mA ≤ IOUT ≤ 400 mA, typical ⊿Vout(⊿Iout) = 0.0005%/mA * Vout

    #4
    The load regulation seems to have difference between table and calculated value.
    Table mentioned 0.0005%/mA , but graph(Calculated value) showed 0.0002%/mA

    Regards,
    Yoshi
  • 0 in reply to Masayoshi Takahashi
    TI__Prodigy 515 points
    #3 Those aren't the value at -40C to 125 in the datasheet, but they can be used to estimate the ⊿Vout(⊿Iout), if the customer needs an idea of the load regulation over temperatures.
    #4 Table shows the load regulation is guaranteed 0(min) to 0.0005%/mA(max). Calculated value from the graph Is within the range.
  • 0 in reply to Min Hudgins
    TI__Intellectual 1530 points
    It means, the customer can use these value as max value? They have to calculate by using max value at -40C to 125C.

    Regards,
    Yoshi
  • 0 in reply to Masayoshi Takahashi
    TI__Prodigy 515 points
    Yes, the customer can use the max value.
  • 0 in reply to Masayoshi Takahashi
    TI__Prodigy 515 points
    Hello Yoshi:
    0.0005%/mA is the typical value, not the max. Vout is guaranteed 1% accuracy from -40degC to 125degC.
    If the customer wants the Vout changes over temperature, use the max 1% accuracy to calculate if 10mA< =Iout<=400mA . For example, if Iout=100mA and Vout is setting 1.23V, ⊿Vout=1.23*1%=0.0123. The max change of output voltage is +/-0.0123V over temperature.