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About SN6501-Q1's Efficiency

Pokkun
Genius 4695 points
Other Parts Discussed in Thread: SN6501-Q1, SN6501

Hello.

My customer is currently in using SN6501-Q1,now.

I have gotten a question about this product .

So, please teach me about SN6501-Q1.

＜Question＞

When we saw Datasheet's Figure1 and Figure3…

I estimate…

That the VDS of the internal FET is different by changing the bias voltage under each condition.

Is this consideration correct?

I want to know that

"why does VIN=VOUT=3V and VIN=VOUT=5V have different characteristics of efficiency?".

※Because I am being asked by customers.

Could you help us?

Best Regards,

Masumi Sekiguchi

  • 0
    TI__Intellectual 2900 points

    Hi Masumi,

    The VDS of internal FET does not change with change in supply voltage. Because the RON of the internal FET also doesn't change by much with supply voltage.

    RON variation (Refer to "Electrical Characteristics" Section 6.5 in datasheet)
    3.3V Supply -> 1 to 3 ohms across parts
    5V Supply -> 0.6 to 2 ohms across parts

    The different figures seen in Section 6.7 are actually characterization of SN6501-Q1 done for different transformers designed with different parameters.

    If you note, there are multiple figures for same voltage configuration but the characterization is done on different transformers.
    Eg: Figure 1 and Figure 7 have same voltage configuration (3.3V->3.3V) but done with different transformers having different turns ratio.

    Please refer to Table 3 in datasheet for complete list of transformers and their parameters to compare with characterization figures.

    Regards,
    Anand Reghunathan

  • 0 in reply to Anand Reghunathan
    Genius 4695 points
    Anand-san, Thank you for your prompt response !

    However, I have a point which I do not understand so much so please teach me a question again.

    I understood that there is a difference in efficiency due to the difference in turns ratio of the transformer.
    However, in Figures 8 & 10 of the datasheet, the transformer of the same model number is used and the input voltage is different.

    Q1：In this case(only the input voltage is different), why does efficiency differ?

    Also,sorry there is another question to add, so please also tell.

    We are considering using this product in combination with PH9185 series.

    Q2：Is there a problem in using PH9185?
    Q3：Is there a parameter to be considered (other than the winding ratio) in selecting the transformer used for this device?

    Best Regards,
    Masumi Sekiguchi
  • 0 in reply to Pokkun
    TI__Intellectual 2900 points

    Masumi-san,

    Please find answers below.

    Q1 : Yes, you are correct. Fig 8 and Fig 10 only differ by input voltage. This is expected as even transformer parameters change with voltage applied to its terminals along with RON of the device which changes very little (check previous reply). So each transformer has to be characterized at different supply voltages also.

    Q2 & Q3 : Please refer to Section 9.2.2.5 of datasheet. Few transformer design parameters are mentioned in this section. There are multiple parameters that need to be considered in selecting transformer for SN6501. Listed Below.

    • Turns Ratio
    • Operating Frequency
    • V-t Requirement
    • Current Rating
    • Low frequency Winding Resistance
    • Magnetizing Inductance
    • Leakage Inductance
    • Primary to Secondary Cap
    • Temperature Range (if required)
    • Isolation Voltage Rating

    I've gone through PH9185 series specifications. Few concerns below.

    • Operating frequency is not mentioned.
    • SN6501 will require an operating range from
      250kHz to 550kHz (Vin = 3.3V)
      300kHz to 620kHz (Vin = 5V)
    • Leakage Inductance is not mentioned. It should be minimized to reduce any voltage spikes during switching.

    Regards,
    Anand Reghunathan

  • 0 in reply to Anand Reghunathan
    Genius 4695 points
    Thank you for your detailed answers, Anand-san !

    By the way my customers are considering 760390014x (manufactured by Wurth) or PH9185.01xNL (made by Pulse Electronics) considering ease of obtaining of transformers.

    Please tell us about these as a reference for transformer selection.（if you are possible…）
    ·What the core material ?(Example：TC 40? or other?)
    ·How many turns (How many turns are actually in 1st and 2nd order instead of turns ratio?)
  • 0 in reply to Pokkun
    TI__Intellectual 2900 points

    Masumi-san,

    I would suggest that you consult the corresponding transformer vendors for this data. They would be able to respond accordingly.

    Thanks & Regards,
    Anand Reghunathan