How to test Slew Rate of AD5560?

Hola, Stitch.

Thanks for your patience. The slew rate of AD5560 is guaranteed by design and not production tested so I cannot give you exact test conditions.

If you are operating at the default compensation configuration (safe mode), it's hard to see any difference between slew rate settings because compensation settings slow the ramp down.

Previous bench experiments with the evaluation board and software shows that we can see the difference in slew rate best when we are in manual compensation and the load is set to open. We got close to 1V/us with that environment but not exactly there.

Please also note that the 1V/us slew rate stated on the datasheet is very likely the expected slew rate at the force amplifier output within the part. Since the signal will still go through the sense resistors and some other components that may contribute extra capacitances, the signal may slow down a bit before going out of the FORCE pin.

Best regards,
Mac

Hola Mac

Thanks for sharing info.

I tested SR setting with both auto & safe mode in no-load and can't see the difference from AD5560 output in between SR0 ~ SR7.  What is the manaul compensation setting in Rz, Rp, Rc, gm, Cf, Cz, Cc3, Cc2, Cc1to test AD5560 slew-rate?

2nd, what is the use-case to set Slew-rate at AD5560?  It only works when manual compensation mode?

Hola, Stitch.

It's hard to recommend Rz, Rp, etc. settings because each system (even the same evaluation board) may have different requirement due to part-to-part variation, so I suggest you play with your setting to find the best fit. The datasheet offers help on identifying these parameters: see the Compensation Strategies section on pages 38 and 39. Identifying the values of your strays and parasitics may still be tricky so you are likely to still adjust for those by playing with these registers.

The Slew Rate control can work with any mode in theory, but safe mode is just designed to be the slowest among all compensation modes, so if it's your compensation capacitors (and parasitics) that limit the speed, you might not see differences when you change slew rate settings.

Best regards,
Mac

Hola Mac

I could understand what you sated in safe compensation.  However, I can't see the difference in between SR0 ~ SR7 by auto compensation.  SR settings should limit the rising time by auto-compensation.  What is missing during testing SR by auto-compensation?

Hola, Stitch.

Setting the part to autocompensation mode is like saying to the part, "I'll let you decide on the best compensation configuration based on the load parameters I give you". Knowing this comes with the understanding that there will be cases when the part will decide to use larger compensation and feedforward capacitors for optimal stability and it's on these cases that you are likely not going to see differences in slew rate regardless of your setting because your compensation caps slow the signal down.

Note: This may be a bit unrelated but if you're planning to use autocompensation, it is important to remember to not overestimate Cr and/or underestimate Rc to avoid overshoot and undershoot scenarios - the very thing we try to address with compensation.

Best regards,
Mac

Hola Max

There are 8 slew rate setting but only 4 gmx setting, 40/80/300/900 uA/V.  How is matching in between each others?