Gate driver for DC motor H-bridge driver - Page 1
Forum section: electronics / projects

author: MarkR42
author_rank: Regular Contributor
timestamp: May 17, 2021, 09:03:23 am
content: Hi,I've been looking at this part:https://www.onsemi.com/products/discretes-drivers/gate-drivers/adp3110aFor driving N-channel MOSFETS in a H-bridge configuration to drive DC motors. (I'd use two of them, one for each side of the motor)The datasheet makes no mention of using it for DC motors and it's not listed in the "applications" section.Assuming that the voltage / current / gate charge / other parameters are all within spec, is there any reason it wouldn't work?I understand that the high side can't be driven with 100% duty cycle because the bootstrap capacitor would eventually discharge, but that's ok, I could just drive it at a high duty cycle.Is there anything obvious I've missed?

author: penfold
author_rank: Frequent Contributor
timestamp: May 17, 2021, 11:20:39 am
content: There shouldn't be too many big differences between that and one designed for DC motor H-bridges.With lower PWM frequencies you will need a larger bootstrap cap and slightly beefier bootstrap diode than recommended and probably a small resistance to limit the repetitive inrush and keeping an eye on what your maximum duty-cycle can be when including the capacitor charging time.Negative transients on the switch node due to either reverse recovery or stray induuctance are worth considering. My mind has gone a bit blank as to how the rating of -5V with 200ns transients to -10V compares with alternative drivers, but doesn't sound aweful unless your planning to use particularly slow fets (also anti-parallel diode reverse recovery also).

author: H.O
author_rank: Frequent Contributor
timestamp: May 18, 2021, 07:01:43 am
content: What's the motor supply voltage?The driver IC can only withstand ~13V so depending on supply voltage and motor drive profile you might need to think about some sort of voltage clamp.

author: MarkR42
author_rank: Regular Contributor
timestamp: May 18, 2021, 07:52:53 am
content: Hi,Motor supply voltage will be up to ~ 20v, the driver chip won't tolerate that voltage on its vcc pin - I'll use a 12v regulator. But higher voltages will still appear on the BST or SW pins throught the high-side FETs. This is ok because in the datasheet allows it.As I understand it, the capacitor between BST and SW gets charged up to about the same voltage as vcc-gnd, or about 12v,and that is potentially added to the battery voltage (on FET high-side) giving ~ 32v between BST and GND. This is higher than the main supply voltage for the circuit - which allows the high-side FETs to be fully turned on into their lowest resistance state.

author: penfold
author_rank: Frequent Contributor
timestamp: May 18, 2021, 11:30:05 am
content: Quote from: MarkR42 on May 18, 2021, 07:52:53 amIs your application particularly cost-sensitive? Since you've mentioned "battery", I'd be a little concerned, unless 20V is the absolute maximum and even with some inadvertent regenerated power from the motor absolutely won't ever exceed 23V... it still doesn't give a lot of headroom. I'd be a little wary of switching noise/transients that could push you over unless the 40V@50ns is more forgiving than it sounds.I'd personally jump up to an NCP81080 (>100V Vmax) (but jumps from 0.20USD to 0.50USD quantity pricing) at least at the prototype stage and be highly critical of the switching waveform for any blips during tests, at which point if all is good, swap to a ADP3110a or consider whether it's cheaper to address the transients with snubbers/filtering/etc or stick with the higher-rated driver.

author: MarkR42
author_rank: Regular Contributor
timestamp: May 18, 2021, 12:01:35 pm
content: @penfold, good call on that, I was trying to get the part which was available, but certainly would be good to have one with more volts of headroom, a slightly more expensive part is not a problem in this case.

author: penfold
author_rank: Frequent Contributor
timestamp: May 18, 2021, 01:17:13 pm
content: Quote from: MarkR42 on May 18, 2021, 12:01:35 pmOh yeah... availability... I forgot about that one! It was just the first one down the list at a lower than $1 cost at a higher voltage so don't read anything more into that IC as a recommendation. I think one of the Microchip ones like that MIC4605 could also be a reasonable fit, though with the inbuilt bootstrap diode (didn't check with the NCP81080) you may need to be a little cautious about peak inrush if you're massively exceeding any recommended boostrap capacitor recommendations.

author: H.O
author_rank: Frequent Contributor
timestamp: May 18, 2021, 02:53:36 pm
content: Quote from: MarkR42 on May 18, 2021, 07:52:53 amThat is correct. I missed the 35V rating the BST pin but still, be careful there if the motor will ever regenerate. Then again, if it's a battery powered device perhaps the battery might absorb the energy, preventing the voltage to increase.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 18, 2021, 02:57:15 pm
content: Bootstrap gate drivers are plentiful. Just check maximum allowed switch node and bst node voltage, as you already did.Minimum switch node voltage is also worth checking, some only tolerate a few volts negative, others can do like -7V easily. If you have large loads or parasitics and fast switching, you are likely to see significant negative peaks on the switch node. You may need to pay premium for this improved rating.Regarding gate drivers aimed for "CPU supplies", when I last time looked at those, there were parts which specified they have some kind of "pre-discharge" self-destruct mode which turns on the low-side FET if there is voltage present at the switch node during power-on, or something like that. I don't remember the details, just said nope. This datasheet doesn't talk about such feature, just worth being careful.With motor loads, you usually choose the PWM frequency in range of 5 to 30 kHz so you can live with slower parts and also use larger gate resistors to slow down switching for EMI improvement.Regarding continued availability, parts like you linked with only intended application being CPU supplies may become obsolete because no one has designed in such a part for the intended application in way over 10 years now. You can find those ICs in 2000 - 2005 era motherboards. If you want to be careful in the current supply situation, you may want to look if you can find a gate driver IC which has pin-compatible secondary sources (or maybe can fit alternate footprints on the PCB).