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DCP021205: Output voltage at light load

Kenji Ohno1
Genius 5095 points
Part Number: DCP021205


Hi Team,

I have some questions that I would like to know about output power as soon as possible.

It is used in Parallel as shown in data sheet Figure37.

 1. The output voltage standard is 75% Load. Is the shipping test inspected with 75% Load?

 2. At light load, it is Typ.7/Max.15 as specified in LOAD REGULATION 10% TO 100% LOAD.

    The maximum output voltage at 5V/100mA is about 5.8V.

    There is no minimum value regulation.How to find the minimum value of 5V/100mA?

   We have created a graph that considers the maximum/average/minimum of expected output fluctuations. Is the understanding correct?

5V Output.pdf

3. The recommended value of Cin described in the circuit diagram of data sheet Figure37 is 2.2uF capacitor at 12V Input.

   If 0.1uF is attached to this Cin, will it affect the output voltage?

  I would like to know the problem caused by not using the recommended capacitor.

Best Regards,

Kenji

  • 0
    TI__Expert 8130 points

    Hi Kenji,

    1. I'm not exactly sure what you mean by "Shipping Test"? Are you referring to if the parts are tested before purchase/shipped? The electrical characteristics table is determined by testing the device across all conditions, which includes 75% load conditions.
    2. Expect a +/- 5% output voltage range. Figure 16 under Typical Characteristics in the datasheet demonstrates typical values across different load conditions.
    3. We recommend to select a 2.2uF low-ESR ceramic input cap to ensure a good startup performance. We cannot guarantee best performance at start-up if not used as recommended.

    Regards,
    Alejandro

  • 0 in reply to iAlejandro
    Genius 5095 points

    Hi Alejandro,

    Thank you for answer.

    Sorry,the shipping test is AT. I understand your understanding.

    I was relieved to have been inspected with 75% Load

    Regarding 2, we understand the typical characteristics of Figure 16.

    When applied to the load regulation calculation formula, it does not fall below ±5% at light load, as shown in the graph sent earlier.

    In the graph I sent, Max. is 5.8V against 100mA/Typ.5.25V. It exceeds ±5%.

    Do you understand this?

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Guru 50120 points

    Hi Kenji,

    I'll let Alejandro answer your question regarding point 2. 

    One question I have is how and where did you get the data/graph for max expected output voltage of 5.8V at 100mA? Is this a bench measurement on your end? The datasheet only details load regulation for 5V output based on typical values which Alejandro mentioned in his previous explanation. Based on Alejandro's response of +/- 5%, I'd expect at loading of 10% (400mA), the output voltage would be +5% of roughly 5.325V on Figure 16 which would be 5.6V. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Genius 5095 points

    Hi Jimmy,

    I calculated from the datasheet.

    VOUT at 75% load and VOUT at 100% load are derived from the graph in Figure 16 and the data sheet specifications.

    　VOUT at 75% load typ.5V max.5.25V

    　VOUT at 100% load typ.4.9V max.5.15V

    　Load regulation = (VOUT at 10% load – VOUT at 100%)/VOUT at 75% load

    　Load regulation typ.7% Max.15%

    Use the Device Comparison Table in the data sheet to find the max. for VOUT at 10% load.

    　0.15 = (VOUT at 10% load – 5.15 )/ 5.25

    　VOUT at 10% load = 5.94

    By approximating, VOUT at 25% load(100mA)=about 5.8V

    Is this understanding correct?

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Expert 8130 points

    Kenji,

    Your understanding is correct.

    The load regulation equation found below the device comparison table is an approximation/guideline. From my experience when working on the lab bench with this device, a good rule of thumb would be to expect a +-5% output range.
    The DCP02 Series is an unregulated converter. Therefore, the output voltage range percentage varies across conditions (e.g., VOUT varies if the application is below or above a 10% load condition).

    Regards,
    Alejandro