> I'm not an analog / power engineer, but I'm not aware of anything that ca= n > switch up to 4 amps at up to 36 volts to an inductive load without kickba= ck > on disconnect. You can't break the laws of Physics - you just have to design to accommodate them :-). Anything can be designed for if you know all the parameters and worst case conditions. Once you do it's just a matter of being prepared to pay for what is required and then 'just doing it'. That's what I meant in my 1st response when I said " I'd suspect that the cheap and nasty drivers fail because they are not prepared to design properly." They probably identified a 50 cents to $1 cost on doing the power supply sequencing and decided it was worth not doing due to the cost savings. ie initial cost won over "may fail. BUT in this case there is no requirement to turn off an inductive load in the in the turn on sequencing requirement. That MAY come in the turn off sequencing. I haven't even started to look at what is involved overall, but if you are switching inductive loads you are going to have to design to handle what happens when you turn them off. if you want the driver to always survive you must design to turn them off under any circumstances. Once you have established this you "just do it". Traditional "tools" include snubbers, back diodes, zener clamps, clamps to double supply rails with a capacitor energy store and resistive energy bleed etc. None of it is conceptually hard to do once you've worked out what is needed. (Some may be hard in practise but that's fine). Identifying the genuine real world worst case requirement is the hardest part. > And I don't see how a resistive feed is going to overcome the filter capacitors in a +5 regulated supply. Identify worst case requirement, Identify & cost alternative solutions. Choose one that suits,. Just do it. You may be able to allow a low enough resistor feed to supply enough energy rate to bring up 5V acceptably fast with filters present. Then you'd have to work out how to deal with the extra dissipation until the 5V source arrives. Probably preferably you'd use a high side transistor feed from HV to LV and turn that off when not needed . You may find that in some cases you cannot guarantee that LV supply will ever come up. Is it OK to run from the HV supply indefinitely ? Probably yes. Work it out, cost it. Decide if it's the best choice. Datasheet: http://www.toshiba-components.com/motorcontrol/pdfs/TB6560AHQ_AF= G_E_2003_20080407.pdf Worst case IC Idd is 5 mA. Say whole LV circuitry needs 20 mA at 5V (example figure, out of head) Say HV supply in this case is 40V. Total dissipation to feed 5V from 40V at 20 mA =3D VI =3D 40V x 20 mA =3D 800 mW. A DPAk or TO220 with modest heatsinking handles this with ease. The 40V supply is good for say 3A to supply stepper so 20 mA is trivial. To bring up 5V caps fast the 40V-> 5V circuit may source current at say 10x load level =3D 200 mA or 100 x load level =3D 2A. Or more. While 40V supply is rising the 5V rail can be essentially hard clamped to it unto V40 reaches 5V. This is a basic regulator circuit. Even an LM317 would probably do it well enough but being able to control it properly may help.. With an LM317 Vout is several volts below Vin, whereas eg a FET can track Vdd and VMx very closely until Vdd reaches 5V. Watch LM317 max voltage in) Avoiding overshoot is desirable :-). Does this satisfy the requirement: "Turn on VDD. Then, when the VDD voltage has stabilised, turn on VMA/B" No, not quite, technically. Vdd rises with VMx until Vdd =3D5V. One would need to check, but with reset etc deasserted it seems unlikely that 5V on VMx is going to cause a sequencing error if truly simultaneous with VDD. The above uses more parts than a basic high side switch for the IC. So it MAY be that no solution that uses HV supply to ring up LV supply is cost effective compared to just using a high side supply switch. That's fine - just use the high side switch. If some other solution is cheaper and it's limitations are livable with, use that. At a glance, and it's only a glance so far, the high side switch seems both essential for correct wort case sequencing and easily doable. Russell McMahon --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .