Mosfet driver TC426 (TC4426) 2 channel 1.5Amax per channel or per unit? - Page 1
Forum section: electronics / beginners

author: eneuro
author_rank: Super Contributor
timestamp: March 25, 2014, 09:00:05 pm
content: Hello,It looks like TC426 (or better newer version with the same pin out TC4426) 2 channel mosfet driver fits my requirements, while I'd like output from logic gate optoisolator 6N137 provide as input to TC426 (or TC427 non-inverting version).ww1.microchip.com/downloads/en/DeviceDoc/21422D.pdfHowever, I'm confused about its specs 1.5Amax gate current ratings.Is it per channel gate current or total per 2 available?If I connect only inputs andoutputs to 2 different mosfet gateson the same low side in H bridge, than totalgate current available will be 3Amax from this driver or only 1.5Amax total while gates toggled at the same time?Is it possible to connect its input channels and output channels together and then I will get something like 1 channel with 3Amax total available?I know, there are other 1 channel mosfets drivers with 2.5A or 3.0A, but it is interesting if I would be able to get 3Amax total gate current from TC426 (TC427) ?

author: Paul Price
author_rank: Super Contributor
timestamp: March 25, 2014, 10:20:55 pm
content: The 1.5A (peak) current output rating is per channel, 2-channels in parallel will give you 3A.

author: eneuro
author_rank: Super Contributor
timestamp: March 25, 2014, 11:00:23 pm
content: Thank you for makeing this clear nowThere is one questionable spec there tooQuoteWhat does it mean?In typical use case I will use TC4426 to drive 2 mosfets gates of two parallel IRFZ44N (http://www.irf.com/product-info/datasheets/data/irfz44npbf.pdf) at once while this driver inputs will be connected together and pulled up to 12-15V battery via 4.7k-10k resistor from output of 6N137 logic gate optoisolator.While I guess this 7 Ohm is output driver channel impedance, so 15VDDmax gives us 15V/7 Ohm= 2.1A~2A gate current,so I need limit this gate current to 1.5Amax and take into account this 7 Ohm series resistance with its gate resistor?15V/1.5A= 10 Ohm, but while output driver impedance is 7 Ohm, so 3 Ohm is minimum gate resistor needed to do not go above this 1.5A gate current limit?I will put 10 Ohm gate resistors, while this switching time is not so critical in this case, but I'd like to know If I had to go to smallest switching time possible using this driver, I should consider using smaller 3 Ohm calculated or maybe I'm wrong with this estimation and this gate resistor should have different value at this maximum expected 15VDDmax to meet its specs mentioned before?

author: Paul Price
author_rank: Super Contributor
timestamp: March 25, 2014, 11:13:57 pm
content: The output drive current is limited by the driver's output circuit design and therefore no external 3-ohm resistor is required if you are using the device to drive a MOSFET gate.

author: eneuro
author_rank: Super Contributor
timestamp: March 26, 2014, 12:46:43 pm
content: Quote from: AhhhChoo on March 25, 2014, 11:38:35 pmDo you mean something like this below?It makes sense.Logic I/O simulation written in C looks good If do not missed something:QuoteWe'll see how it will perform

author: eneuro
author_rank: Super Contributor
timestamp: March 26, 2014, 04:18:59 pm
content: Switching speed will depend on application, but I expect high currents from time to time need to be switched ON/OFF.In one battery overvoltage protection analog circuit I run into problems with simply driving mosfet gate by optoisolator, however it was slow one without Shmitt output (PC817). Frequency started to rise I guess, while sometimes voltage detection limit will oscilate depending on regenerative braking and battery condition and external load in electric vehicle BLDC/Induction motor driver also currents may be high and switching bigger currents require faster switching on/off else it is easy to burn mosfets.I'd like to have bigger edge and there is no chance to do it without mosfet driver.It can be also used in 3 phase H bridge motor driver where additional optoisolator will simpy allow disable and put low all mosfet gates by pulling down 6N137's VE pin (normally pulled up in this sample optoisolated gate driver).QuoteSo, this optoisolated gate driver can have many use cases, so I had to try to know its limits before implement it in one of my projects, to ensure I will be able diagnose and resolve issues based on its specs