Hello Mr. Rao,
I would like to use the SN6505b to output two regulated voltages with (LDO). : 5V and 3V3 and at least 500 mA (or more) at 5V. The Input voltage at the Primary side should be 5V. I have checked the datasheet and it suggests the tranformer "750315371" for 5V to 5V applications but without LDO. for the 5V Output. I would really like to use LDO for the 5V since the voltage should be really stable. Do you have a siggestion for another transformer? This one has got the turns Ratio 1 : 1.1 I think I Need at least 1.4 or 1.5.
What about the 3.3V ? is there any issue when connecting the second LDO for 3V3 at the Output of the 5V LDO one?
If using the unregulated 5V Output as suggested by the datasheet, could you please tell me how stabble it is? Is it suitable to supplying any usb Port for external USB Memory for example?
As General question : What is the Minimum Input current i should supply at 5V to the SN6505B Input to get about 500mA. Is the switching frequency after powerering up the device always constant? Does it always Switch 1A all the time all the time
Thank you in advance.
In reply to Koteshwar Rao:
Thank you for replying and the detailed Information. Regarding the turns-Ratio I also got the same values before (Nmin = 1.25). But in the datasheet on page 3, you only recommend the "750315371 " for 5 to 5V applications. In the example for the calculation of the V-T product of the SN6505B, you used different switching frequencies for both Input voltages (3V3 250kHz and 5V : 300kHz ). I can just find in the datasheet one minimum Switching frequency (363kHz). I used it to calculate my V.T Product at 5V iput voltage 5.5V / (2*363kHz) = 7.5VµS. Is it the right frequency?
I have found the transformer "750316028" with turns-ratio 1.7 and 1A. So that I can get about 9V at the Output and use a LDO for 5V Output? What do you think? .In the datasheet you only recommend it for 3V3 to 3V3 applications.
Sorry for the detailed questions but I need more Information because we will not have any redesign for this product. So it Needs to work in the first turn.
Thank you for your Support.
In reply to Gilbert Kuate:
Yes please go ahead and use 363kHz for calculating the VT product for your application. The examples given in the datasheet are mock calculations and are not there to show default clock frequency of SN6505.
Could you please share you email ID? I can share additional details over email.
Thanks & Regards,Anand Reghunathan
In reply to Anand Reghunathan:
Thank you for replying. Here is my email address : email@example.com
Regardig the frequency "363khz" used for the calculation of the VT product. Is it in this case for 5V or 3V3? or both? I used it for 5 to 5V Regulation.
Please also let me know about other questions I asked before regarding the chosen transformer in order to have a 5V LDO regulated power supply with at least 500mA.
Thanks in advance
After checking the different transformer offered by Würth Elektronik on his Website (see Picture above) they have already defined Input voltages for each one. But the one they recommand for my application (5V to 5V) does not require any LDO at Output. But on my Opinion it is important for me to have some 5V LDO. I have calculated the turns Ratio at least 1:1.3 if usind an LDO. the suitable one I wanted to Choose was : 750316028 with 1:1.7 turns Ratio. But they only recommand it with an Input voltage of 3V3. Is there any issue if using them with 5V Input? is it suitable to my application or I should use 1:11 one without LDO?
Thank you for your Support
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