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UC1846-SP: Freq and Dead Time Calculation

ee tech
Prodigy 220 points
Part Number: UC1846-SP
Other Parts Discussed in Thread: UC3856, UC3846,

Need confirmation that the equations shown for frequency and dead time calculation is correct.

The equations (4) and (5) don't seem to match the values shown in table 1 for figure. 8.

If I plug in the values shown for Ct and Rt, into the equations, the results to do not match the values in table 1.

Results:

F=220 KHz, Td=152.3 ns

Please advise.

  • 0
    TI__Expert 7445 points
    Hi ee tech

    I am looking into it and will provide you update on it.
  • 0 in reply to Ramesh Khanna
    TI__Expert 7445 points
    Hi ee tech,

    1. Dead time information in Table 1 ( pg 15) td = 75.8ns is not accurate. Datasheet should be revised to update some inaccuracies.
    2. As the part is 30+ years old, thus more information can be found in various application notes done by veteran engineers no longer around.
    See attached app note:
    www.ti.com/.../slua075.pdf
    Note Figure 7 graph in the app note showcases that Td would be between 145ns - 200ns per typical published graph.
    Also note oscillator discharge current highlighted in Fig. 5 of app note is about 12mA. however based upon some of the actual measured data it is typically 7.5mA with spec limits of ( 3mA - 18mA)
    www.ti.com/.../slua178.pdf
    Attached App note showcases the discharge current of UC3856 ( 6.7 - 8.8mA) which is an improved version of UC3846.
    3. Oscillator frequency does have tolerance as indicated in the datasheet about +/- 9.3% for given RT CT.

    Another good source of information is - review app notes for additional information.
    www.ti.com/.../technicaldocuments

    In order to get more accurate data UC1846-SP would have to be bench characterized and then datasheet updated to reflect the updated information.