Other Parts Discussed in Thread: TIDA-010057, , CSD19538Q3A
Good Morning/Afternoon Texas Instrument Support,
thanks for your support until now.
I am trying to use a SEPIC/CUK combination to create +80V and -80V (the one reported in TIDA-010057 https://www.ti.com/tool/TIDA-010057 ) but the LM3488 do not start.
Using an oscilloscope I do not see any
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You originally used 74404084101 (semishielded, WE-LQS 100uH 1A DCR=290mOhms) for L1.
For EMI reason I have instead used 7687709681 (WE-PD HV 1210 680uH 0.80A 1.15Ohm).
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You originally used 744043102 (shielded Ferrite 1mH 80 mA 7 Ohm, no information about maximum tension that could be supported) for L3 and L4.
To be on the safe side (high voltage working is certain "Designed for 400VDC Applications" according to https://www.we-online.com/catalog/en/WE-PD-HV ) I have used 7687709682 (WE-PD-HV , 6.8 mH, 280mA, 8 Ohm)
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I use the same MOS CSD19538Q3A of your design. All other parts are the same or equivalent.
Because the inductor are of higher value I was expecting them to work with less current ripple (not 40% but 6.66% instead)
Pin FA/Sync/SD is at 0.738V even if it connected trough 68Kohm to GND.
According to page 7 of https://www.ti.com/lit/ds/symlink/lm3488.pdf?ts=1630909270695 it seems to me that is undefined; with an oscilloscope I have verified that it is pure DC (no oscillation is present)
Vsense is around 0.005 -0.010V DC (no oscillation).
Best Regards and thanks for your time.