Other Parts Discussed in Thread: SN6505A, SN6501
Hi Team,
can SN6505 meet 5V to 5V@3W isolated power requirement? if so, should I choose SN6505A or SN6505B?
if not, do you have other easy and low cost solution to recomend?
Thanks.
Regards, Sunny
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Hi Sunny,
Thank you for posting to E2E! SN6505 devices are capable of sinking up to 5W for 5V to 5V (~1000mA) isolated power applications, regardless of "A", "B", or "-Q1" versions. These are our only push-pull transformer drivers capable of providing 3W since SN6501 can be used for up to 1.75W 5V to 5V supplies.
SN6505B is our typical SN6505 recommendation due to its higher internal switching frequency. Although SN6505 devices can be connected to an external clock, the SN6505B's higher default switching frequency allows for compatibility with more off-the-shelf push-pull isolation transformers and smaller transformers that are commercially available due to its lower V-t product requirement.
Will this work for your application? Please let us know if you have additional questions!
Respectfully,
Manuel Chavez
Hi Manuel,
Many thanks for your comments, but as i know if output 5V@3W, that will need 1.5A peak current(maybe 2A, consider transformer efficiency), while SN6505 only support 1A, do you have any test date to show that?
THanks very much.
Regards,Sunny
Hi Sunny,
You're welcome. It is not recommended to operate SN6505 with >1A sinking through its D1 and D2 pins. During the 1.5A peak currents, SN6505's integrated current-limit and thermal-shutdown protection features will prevent damage to SN6505 by turning the device off and continuously attempting to resume normal power transfer operation until load currents decrease to safe levels.
SN6505 is also designed to power large load capacitances, so i f the 1.5A transient is on the order of micro- or milliseconds, a large output capacitor can be used on the isolated power supply output to supply this charge without affecting the SN6505.
Thank you,
Manuel Chavez
Hi Manuel,
That is the issue, we know that SN6505 can only support 1.5A switch ccurrent, but for 5V to 5V@3W isolated solution, could you help to inform the switch current in this applicaiton? In my estimation, the switch current should about 1.5A...
THanks.
Regards, Sunny
Hi Sunny:
As Manuel pointed out, we do not recommend using SN6505 for applications where primary side switching currents exceed 1A. Please refer to Recommended Operating Conditions table in the datasheet for more details.
However, if I understand your requirements correctly, your application require 3W output with a 5V IN, 5V OUT configuration. This means that the output current is 3W / 5V = 600mA. There are multiple transformers recommended in Table 3 of the datasheet for this requirement; see below.
Please let us know if you have any additional questions.
Regards,
Dushmantha
Hi Dushmantha,
Many thanks for your comments.
Is there any documents to show how to caculate switch current of SN6505, for example, 5V to 5V@600mA, if use the transformar in table 3, how much swich current will happen on SN6505?
Thanks.
Regards, Sunny
Thanks Dushmantha.
Sunny,
An estimate of how much current the SN6505 will sink, I_primary, can be made by multiplying the load current and transformer turns ratio:
I_load x N = I_primary
Additional current will be consumed due to system parasitics, including transformer magnetization, which can combine to ~25mA. This will vary based on transformer part number and load current. If the N = 1:1.5 transformer Dushmantha showed above is used (DA2303-AL), I_primary can be calculated as below:
(600mA x 1.5) + 25mA = 925mA
Please let us know if you have additional questions or comments.
Respectfully,
Manuel Chavez