Gate Drivers: Separate source and sink outputs - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: June 28, 2018, 02:36:48 pm
content: Hi,I found the circuit attached in the datasheet of the gate driver 1EDI60N12AF. I've seen other gate drivers which offer separate source and sink outputs. What can really be achieved by doing this separation in comparison with those which don't offer this feature? I mean, I guess you manage to control the charging and discharging current, but what are the pros and cons of this? When is this feature truly recommended?

author: XaviPacheco
author_rank: Regular Contributor
timestamp: June 28, 2018, 03:50:02 pm
content: Another brief question on the schematic.The datasheet says: The 1EDI60N12AF provides output currents of at least 6 A at separated output pins.My 12V supply max current is 5A. So, I should certainly select a resistor to limit that current, right?

author: CopperCone
author_rank: Super Contributor
timestamp: June 28, 2018, 03:51:20 pm
content: I think it might also be relevant when interfacing with totem poles

author: CopperCone
author_rank: Super Contributor
timestamp: June 28, 2018, 03:56:46 pm
content: What applications require faster discharging then charging? Can you explain emi behavior quickly ?

author: Siwastaja
author_rank: Super Contributor
timestamp: June 28, 2018, 06:04:51 pm
content: I'd add that when driving a typical MOSFET gate from a typical voltage source of 0V/12V, there is a rise / fall time asymmetry coming from the asymmetric "distance" to the Vgs(th). When turning on, the threshold (at about 3-4V) is reached quickly, and charging the Miller capacitance at Vgs=3-4V happens quickly because there is still a significant voltage differential, let's say 12-4 = 8V, pushing charge through the total gate resistance.But when turning off, we are only driving to 0V, which means, at the threshold, where the losses happen, we have only about 3-4V difference available, meaning less current through the fixed total gate resistance.So, for this reason, too, you'd want to have lower resistance for turn-off, to fight against the asymmetry which happens in the undesirable direction. If you want to have asymmetry in the favorable, opposite direction, the difference between the two external resistors is often going to be quite big (think about 10R for turn-on and 1R for turn-off?)Lower resistance for pulling down also helps to avoid the upper device in a half bridge from accidentally pulsing on due to coupling from the lower device. Not sure if this happens in smaller MOSFET bridges, but this (lower resistance, low saturation voltage Miller clamp) seems to be a big marketing argument for IGBT gate drivers when negative supply is not available.Finally, it would make a lot of sense to supply the gate drivers from, say, +12/-5V instead of the typical +12V/0V, but such negative supply is seldom available, so the practicalities and price dominates here - single-sided supply is "good enough", and having separate source/sink pins comes practically for free (especially if the package they would use anyway would have NC pins otherwise).

author: XaviPacheco
author_rank: Regular Contributor
timestamp: June 28, 2018, 06:17:08 pm
content: Thank you.I intend to use that gate driver circuit to control a brushed dc motor via PWM.

author: CopperCone
author_rank: Super Contributor
timestamp: June 28, 2018, 06:44:18 pm
content: Hmm quite a bit of bipolar drivers specify rails that are equal. Is this an error then? i.e. +-12V

author: CopperCone
author_rank: Super Contributor
timestamp: June 29, 2018, 12:50:59 am
content: for instance the ISO5500 datasheet.Are IGBT different?

author: CopperCone
author_rank: Super Contributor
timestamp: June 29, 2018, 04:30:17 pm
content: Quote from: blueskull on June 29, 2018, 02:25:02 am

author: CopperCone
author_rank: Super Contributor
timestamp: June 29, 2018, 04:31:40 pm
content: I had no idea. I just experianced confusion.