I've been reading the TB6560 driver chip data sheet.. you can find it here:
The interesting part to me is on page 28, where it says:
So... there are a couple of thoughts that come to mind after reading that:Power-on Sequence with Control Input Signals
Turn on VDD. Then, when the VDD voltage has stabilized, turn on VMA/B.
Hold the control input pins Low while turning on VDD and VMA/B.
(All the control input pins are internally pulled down.)
After VDD and VMA/B completely stabilizes at the rated voltages, the RESET and ENABLE pins can be set High. If this sequence is not properly followed, the IC may not operate correctly, or the IC and the peripheral parts may be damaged.
A power-off sequence should be the reverse of this sequence
First, has anyone ever seen that documented in the operating instructions for a TB6560 based driver? Like all those cheap ones from China and Hong Kong that are being sold on ebay.. do ANY of those say "um... by the way, don't turn on the motor power until after the logic voltage is up, and turn off the motor power before you shut down logic power."? Or do any of them have some magical circuitry to prevent the motor power from coming on until after the logic supply has settled?
Secondly, how on earth would you even do that in a driver that depends on a separate power supply? Keeping the logic power on after motor power goes down isn't hard, the caps in the regulator circuit will do that, but the power up sequence is the trick. If you were building a complete system, and you could build two power supplies (one for logic supply and one for motor supply) and you built in a timing control that flips on the one first and then the other, then, yeah... that's possible. But if you just sell a driver, and you have the user hook up any old power supply for motor and logic without warning them... or you have an onboard +5 regulator to supply the logic power from the motor power supply... how do you set that up so it doesn't fry the chip?
I started off wondering why so many people who buy these crap TB6560 drivers end up frying the chip, and NOW, I'm wondering how any of them work at all!
I started looking into this after reading:
http://www.cnczone.com/forums/genera...se-24.html#281 so I'm not the only one who has noticed this problem...
I'd honestly like to hear if there is a good electronic solution to that problem. I'm not an analog electronics expert, or a power systems designer by any means. Maybe there is some way of doing this power up sequence with ONE power supply that I've not heard of?
The capacitors and current limiting in a standard +5 voltage regulation circuit pretty much guarantee that it will come up to +5 volts slower than it's supply voltage turns on. I guess you could add a great huge power resistor between the motor supply and the chip and put a great huge high voltage capacitor right there so it also comes up slower but A) high wattage resistors and high voltage high value caps are expensive and B) you would loose supply power due to the resistor. That's why people didn't like the old style of linear supplies.
Another obvious idea would be a relay, but then you are controlling an inductive load and as soon as the relay breaks, you are going to get a nice healthy back EMF spike which will kill the chip anyway. (Datasheet, page 32, point 3).
I guess you could hook your motor power supply INPUT up to a relay... but then you need a separate supply for logic power again...
Bottom line: TB6560 = 2 separate power supplies and the first one has to turn on the second one after a time delay. OR... it's going to fry eventually. No?