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SN6505B-Q1: Details regard the above driver and its best fit transformer

Ohad Fundoianu
Intellectual 380 points
Part Number: SN6505B-Q1
Other Parts Discussed in Thread: SN6505A-Q1, SN6505A, SN6505B, SN6505D

Tool/software:

Hello, 

I would like to use  SN6505B-Q1 for isolating power for ECG use. I would like to know: 

1. What is the difference between  SN6505A-Q1 SN6505B-Q1 or  SN6505BDQ1 except for the minimal frequency ? 

2. In the datasheet there was a table with " Recommended Isolation Transformers Optimized for the Device". Is it must using only them with the device ? If I found conditions are met with other transformer isn't it possible to use it ? 

For example: 76253/35ENC of MURATA with 1:2.23CT is not OK to use with that driver? 

Thanks, 

Ohad

  • 0
    TI__Mastermind 29345 points

    Hello Ohad,

    1. The difference between the SN6505x versions is the switching frequency, slew rate and soft-start.
      1. SN6505A supports up to 600kHz 
      2. SN6505B supports up to 1.6MHz
      3. SN6505D supports up to 1.6MHz with soft-start disabled. 
    2. Yes, you can use other transformers. The recommended transformers table are parts that we have tested and found to work well with the SN6505.
    3. 76253/35ENC transformer looks good. In general, the transformer must have a greater VT product than the equations in 9.2.2.5.1 V-t Product Calculation in order not to saturate. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    Intellectual 380 points

    Hi Andrew, 

    I saw we already have in our system the "SN6505B" which looks prity much the same to SN6505B-Q1. 

    1. What is exactly the difference between them ? 

    2. In regards to the explanation written inside the datasheet on the "Turn Ratio Estimate", it was written to consider the "typical efficiency of 97% into account" when choosing the transformer. 

    Where does the 97% come from ? Does it always 97% ? Or it should be taken from the graph of the according transformer ? 

    For example, if I want to work with SN6505B + Wurth 750316028 under current of 700mA, Vcc=3.3v, wouldn't it be more correct to take efficiency of 77% which will end in the formula as 1.298 instead of 1.031 ? 

    See below taken from the datasheet ? 

    Thanks, 

    Ohad

  • 0 in reply to Ohad Fundoianu
    Intellectual 380 points

    Another Question : 

    How exactly do the drains D1 and D2 are Tri-stated dependent on the Enable pin ? 

    According to the scheme it seems that the two internal N-channels MOSFETs are only controlled through the gates. If that so than what will happen when En pin is low (SHDN) while Vcc of the transformer still exist ? Is there a chance that Vcc will still drop on the N-channels FETs between Drain to Source on the bulk while Gate input = '0' ? 

    I based my self on the following block diagram when having this suspect : 

     

    Ohad

  • 0 in reply to Ohad Fundoianu
    TI__Mastermind 29345 points

    Hello Ohad, 

    1. The difference between devices with the "Q1" designator is the automotive qualification (AEC-Q100) devices go through additional testing which is typically required for automotive customers. The non-Q devices are intended for industrial applications. 
    2. 97% is a general estimation. You are correct that the datasheet plots are a better indicator. Please use the transformer datasheet or the datasheet efficiency plot for a transformer and load condition for a more accurate indication of how a transformer will perform. 
    3. When En pin is low (SHDN) and the device is powered, the D1/D2 pins will be open/floating and not conducting. As long as the absolute maximum conditions are not exceeded, there is not risk that VCC will conduct from D1/D2 to GND while in shut down mode. 

    Best,
    Andrew