How can any TB6560 driver design NOT violate the chips spec's?

[neilw20]

Nah, just a hot air gun. Bit frightening?

[H500]

I tried a hot air system at work, but the chip was so small that it kept getting blown off the board.

[RomanLini]

Any industrial-suitable stepper driver chip will have a package with a large metal pad, and be *bolted* to a heatsink.

[Marc N Fournier]

Saw my name here so thought I would add. My Tb6560 Blue board from H*** died as it fried the Z axis chip. Somehow ALL the chips died at the same time. I ordered 5 of them just to play around with this.

I removed both the 12V and the 5V regulator from my Blue board from H***.

Soldered in 2 connectors to supply power from a PC power supply; 12V (fan and relay) and 5V for the logic. So now I resolved the overheat issue of the 12V regulator and have independant control of both power supplies during power on.

Scoping the Blue board from H*** i find the enable pin of each of the 4 TB6560 axis do not go high at the same time. I can not figure out why they would do this. X axis is quick to respond but other three take more time. May have something to do with MACH3 overhead.

Why do they use a HEX inverter chip (74hc14) going to the OPTO (PC817). I can understand the Opto (to a point) but the inverter, no. If you want this buffer to get a clean signal, why not use a non-inverting type. I read very low voltage comming out of the opto to the TB6560 CLK and CW/CCW pins.

I have another 4 axis, TB6560 based card from a Canadian source. This card does not have any opto, no buffer. Just the parallel port BOB to the TB6560. So far this 4 axis card is working much bettre than the BBFH*** (after some teething pains).

Marc

[lazzymonk]

has any one tried the single axis tb6560 boards? Im new to cnc and dont want to spend more than I have to but cant find anyone that has used, or even seen these before.

3A TB6560 DC Stepper Motor Single Axis Drive Controller | eBay

[James Newton]

Reading over the TB6560 datasheet again, I noticed something else:

When you look at the actual power dissipation, (page 6 on the data sheet)
http://www.toshiba-components.com/mo...3_20080407.pdf
it handles LESS than 43 watts (43 watts with an infinitely good heat-sink, which doesn't exist) which is only a bit over 1 amp at the max 40 volts. Even with a 24 volt supply, it will fry above 43/24=1.8 amps. Only using 19 volt power brick? It will fry at 43/19=2.25 amps. Actually, it will fry before that, even with a really good heat sink.

[doorknob]

James, just a question about interpreting the spec sheet with respect to the max 43 watts dissipation figure. I'm not sure that I agree with your calculations, but then I haven't completely scoped out the fine print in the spec sheet, and I may very well be missing something (and, as I mention below, I think that there may even be a problem with one of the equations in the spec sheet).

From page 28:

Power Dissipation

The power dissipation of the IC can be calculated by the following equation:

P = VDD × IDD + IOUT × Ron × 2 drivers

The higher the ambient temperature, the smaller the power dissipation.
Examine the PD-Ta characteristic curve to determine if there is a sufficient margin in the thermal design.


My interpretation of VDD and IDD is that it represents the power to the control section of the chip (at 5 volts and perhaps 5 mA), whereas the power dissipation related to the load would be based on IOUT times Ron times 2 (but then, I would have expected that power to be calculated as IOUT-squared times Ron times 2, so I'm wondering whether that formula is wrong).

As far as Ron is concerned, I would expect that to be fairly small, as I would expect it to be operating in a switched mode, not a linear mode - page 8 shows that as max of 0.4 ohms.

But I don't completely understand how the chip implements microstepping in the switched mode - does it act as a switch throughout all of the portions of the sine/cosine waveform generation? Probably yes, but I haven't yet figured out how it does that.

(edit: I guess that it does current limiting to generate the sine/cosine waveforms, which it obviously can do in switchmode)

If power dissipation inside the chip is really dependent on IOUT-squared times Ron times 2, then at 3.5A for I and 0.4 ohms for Ron gives a very small number which is not close to 43 watts.

(edit: I calculate that as approximately 5 watts times 2, for a grand total of 10 watts at maximum rated load current)

So, what am I missing here?

I can't stick around to discuss this right now, but maybe later tonight I can revisit it.

[H500]

Doorknob, I think their equation is wrong. Ignoring switching losses, the heat produced by the chip can be estimated as 2 x .5 ohm x 3.5amp x 3.5 amp x .7 = 8.5w

[doorknob]

Doorknob, I think their equation is wrong. Ignoring switching losses, the heat produced by the chip can be estimated as 2 x .5 ohm x 3.5amp x 3.5 amp x .7 = 8.5w

Is your derating factor of 0.7 because you expect that both windings will not be fully energized at the same time, or due to something else?

[neilw20]

I squared R. that's physics.
And the switching losses can be considerable and there is little information the spec sheet.
And if the flywheel diodes are conducting a high current occurs for the reverse recovery time of the diode. That's physics.
No specs on the diodes there I notices either.

There is also a section in the specs about a 'fast' fuse.
Considerable derating is required for a 'fast fuse'.
The term fast, is not really a good term.
The I squared T rating of a 'fast' fuse is much lower, so the fault current during the arcing phase as the fuse blows is lower.
A fast fuse once arcing can keep the fault current within possibly 10% of the rated value, but a 'normal/slow' fuse may arc at 200-500%.
The time the fuse arcs for is dependent on many things.

The spec sheet says use a 'fast', and looking at fuse specs, it is quite possible for the silicon to act as a fuse as many have discovered.

And then there is leakage inductance/capacitance in the steppers that will increase dissipation during switching. significant at chopping frequencies.

3.5 A is the absolute max, and considerable derating for normal operation is needed. As James says, you need a good heatsink.

You can't just multiply by 0.7 because of the times the windings are on.
That makes little difference. It is all about losses because the thing runs in switch mode, and both channels are conducting ALL the time.

The phasing of the switching can mean both conduct at the same time.
The phasing is a function of the current limiting at a given instance.

Test in real application, and you will see how big the heatsink needs to be!
I wonder why the spec sheet says 43W?

[H500]

The .7 is for the RMS current, since the waveform is sinusoidal.

[James Newton]

I believe that is the ability of the chip when used without a heatsink. Notice graph top of page 27, where the Pd-Ta line 3 for "Chip without heatsink" is about 5watts. I was talking about the maximum possible wattage with an infinite heatsink, which is line 1 on that graph. Line 2, which is for a 3.5'C per Watt heatsink (that's a pretty good heatsink) and which shows about 25 watts max. So these things are really designed for 1 amp at 24 volts or maybe 2 amps at 12 volts WITH a reasonable heatsink. Half an amp at 40 volts. It's a wonder they hold up as well as they do.