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SN6505A: Two SN6505A applications

Part Number: SN6505A
Other Parts Discussed in Thread: SN6507

Hi Team,

Could you help our customer's concern. I have posted their inquiry below.

I have a device that outputs 3~4.2VDC. Can I use the following topology to get around 30~42VDC

the vin is 3VDC to 4.2VDC not 12VDC. i HAVE TWO QUESTIONS BACK TO BACK i WANT TO ASK YOU

Output is 200mA

ratio of transformer is 1:10

Name of transformer: 750032051 link: https://www.we-online.com/catalog/datasheet/750032051.pdf

I have a second question

using the same topology, I have a device that outputs 12VDC @ 1A. I would like to isolate the 12VDC to output dual 5VDC

The first one. Input 3~4.2VDC @ 200mA Expected output 30~42VDC

The second one. Input 12VDC @ 1A Expected output dual outputs of 5VDC

Please see attached file:

attachments_schematic.zip

Best regards,

Jonathan

  • Hi Jonathan,

    Thanks for reaching out.

    SN6505 can support power supply solutions of upto 5W input power. But I see that the first request from customer is for 42V @ 200mA is for 8.4W output power and the second request of 12V @ 1A at the input is 12W input power. Both are exceeding SN6505 supported ratings and hence, the device cannot be used as is for supporting these requirements.

    If customer could add external FETs as shown in the below diagram, then they could increase the input current to higher values and are only limited by the external FETs. SN6505 only supports an input voltage of upto 5.5V but the below approach enables the solution to be used for higher voltages and only only limited by the FET voltage ratings. Please see below E2E post for more information and discussion related to this solution.

    https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/958704/12v-transformer-driver-for-isolated-gate-drive-power-supply-requirements/

    Let me know if customer has any questions, thanks.


    Regards,
    Koteshwar Rao

  • Hi Koteshwar,

    Here is the customer's feedback. Thank you for the support

    After reviewing the previous schematics, I would like to make some minor corrections. Sorry for any inconvenience. I have attached a new and better schematic. Disregard the previous schematics because they had some minor errors therefore, kindly use the new schematic I have attached here 

    Note: Current for 12VDC is 1A and 3~4.2VDC is 200mA

    Best regards,

    Jonathan

  • Hi Jonathan,

    Thanks for the updated schematics.

    This schematic has 12V applied to VCC of SN6505 but the voltage supported at VCC is 2.25V to 5.5V. Hence, 12V input cannot be applied to device directly. The E2E post link that I had provided previously describes an approach where you can modify SN6505 circuit to still support 12V input. Please refer to the that E2E post. I am also giving you an example of another E2E post related to 12V input supply, please see below.

    https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/906766/sn6505a-12v-12v-isolation-power

    This schematic is okay but the supported power levels shouldn't exceed 5W at the input. I see you mentioned the input current requirement as 200mA at 3V to 4.2V supply. If this is the requirement then this schematic should work fine and SN6505 will be able to support this current at the input. Thanks.


    Regards,
    Koteshwar Rao

  • Hi Koteshwar,

    Thank you! On behalf of our customer here is their response:

    I have been following the e2e thread. The response is positive. Concerning the 3VDC~4.2VDC, the engineer said it can work, therefore, my last question regarding the 3VDC~4.2VDC input is, can it quadruple the input voltage as shown in the schematic?
    The formula I am using for quadrupling the input voltage at the output voltage = 4 x number of transformer secondary turns x input voltage
    i.e T1 min output voltage = 4 x 2 x 3 = 24VDC
    T2 min output voltage = 4 x 3.9 x 3 = 46.8VDC
    T1 max output voltage = 4 x 2 x 4.2 = 33.6VDC
    T2 max output voltage = 4 x 3.9 x 4.2 = 65.52VDC


    For the 12VDC@1A, I am planning to use SN6507 as it accepts 3VDC~36VDC. Nevertheless, I am having a hard time understanding if it can accept 1A to function properly without blowing up during operation, therefore, may I send you a schematic diagram of how I will design the circuit? I have tried to use the TI power designer but the SN6507 is also not supported.

    If you take a look at the SN6507 specs. the Switch current limit (Typ) (A) is 1.3 and the output current (A) is 0.5, therefore, will it support the 1A at the input. I will send you a schematic soon for the SN6507 to have a more in-depth understanding of the circuit.

    Best regards,

    Jonathan

  • Hi Jonathan,

    Thanks for sharing additional inputs.

    Yes, the SN650x based solution can quadruple the output as long as the power and current levels are under device ratings. For SN6505, the input current shouldn't exceed 1A and the input power shouldn't exceed 5W.

    The output voltage primarily depends on transformer turns-ratio and the SN6505 doesn't directly influence. Please use the below formula from SN6505 datasheet (section 9.2.2.5.2) for calculating the turns-ration for desired output voltages.

    SN6507 supports an input current of 0.5A and doesn't support 1A input. Since the SN6507 supports higher input voltage, it also supports higher input power of upto 18W (36V*0.5A). If require dual outputs of 5V @ 1A each, then an input voltage of 12V @ 0.5A should be sufficient to get the dual outputs of 5V @ 1A each.

    Let me know if this answers your question, thanks.


    Regards,
    Koteshwar Rao

  • Hi Koteshwar,

    In behalf of the customer, thank you for the support. You may close this thread.

    Best regards,

    Jonathan