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|  | ericmar
on 09/15/2008 at 03:53 AM
| Category(s): | Technical Questions, power.national.com |
| Subject: | Designing SEPIC using LM3478 |
| Message: (Notified via email on every direct response) |
Hi,
I am designing a SEPIC converter using the LM3478. My design requirements are:
V_IN = +4.8 ~ 12V
V_OUT = +5.5V @ 2.5A
I found that there is an application note, AN-1484 Designing a SEPIC Converter, which explains the way to design a SEPIC converter with an example using the LM3478. However, it seems that the formula there is a bit different from the SEPIC design section of LM3478 datasheet.
For example, the formula of duty cycle calculation omits the subtraction of V_Q in the App. note. I wonder if it is so small that it can be neglected.
Also, the formula to calculate the R_SEN or R_SN is different in both documents. What is the relationship between the V_SL and delta V_SL as mentioned in page 19 of the LM3478 datasheet?
Another question is that in page 5 of the App. note, the current sense gain, G_CS, is specified as (roughly 1/R_SN) 100A/V. Then the G_CS in the calculation of page 6 is taken as 91, which I am not sure how this value is obtained because the calculated R_sn equals to 19mohm.
Please advise. Thanks.
Regards,
Eric
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