HT1632C matrix settings - P-MOS vs N-MOS - Page 1
Forum section: electronics / projects

author: danners430
author_rank: Regular Contributor
timestamp: April 16, 2019, 12:11:16 pm
content: Afternoon folks,I'm a little confused when trying to set up the HT1632C LED matrix driver (datasheet -https://cdn-shop.adafruit.com/datasheets/ht1632cv120.pdf) - there are four modes described as belowN-MOS open drain output & 8 COMN-MOS open drain output & 16 COMP-MOS open drain ouput & 8 COMP-MOS open drain output & 16 COMObviously I know what the 8/16 COM means (the chip can either control a 32x8 or 24x16 matrix), but which would I choose between N-MOS and P-MOS?It seems like something I should know, so I don't know whether I'm having a bit of a blonde moment, or whether it's something obscure...A bit of background to the project, if it helps - each chip will be controlling six 8x8 matrices, arranged as 24x16. Each matrix has all eight rows & columns exposed, so no common anodes or cathodes.Thanks for the help in advance!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2019, 12:15:07 pm
content: Offhand -- sounds like it has to be chosen appropriately for CA/CC displays. A matrix is both, so you should need PMOS for the high side (whichever those are, rows/cols) and NMOS for the low side (cols/rows). A full active (CMOS) level is acceptable too, for example I've wired an 8x8 matrix (8 digits of 7-segment plus decimal) between a pair of 74LS273s, works just fine.Tim

author: danners430
author_rank: Regular Contributor
timestamp: April 16, 2019, 01:07:26 pm
content: I suspect my blonde moment theory was correct - Looking more closely at the datasheet, I noticed something blatantly obvious which I managed to miss...These options are for the Commons, not for the rows. From this, I'm guessing that this setting is to swap the commons from the current sink for the column, to a transistor driver when used with higher power LEDs, and this setting in essence inverts the state of the output, to make it easier to drive P-MOS transistors / FETs?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2019, 02:09:31 pm
content: So let's see...There are in fact sourcing and sinking data, for both pin types, so that's neat. It's... well, I guess it's not necessarily full CMOS output, but it could be, which would get you a nice full waveform (inactive rows held low, inactive columns held high). If they aren't driven full wave, but gated to be only open drain (P or N), and both pin types can be configured either way (noting that the P/N drivers themselves aren't equivalent, with the row N's being weak (16mA) and the com N's being very strong (350mA)), then that would be helpful for adding drive transistors, which of course invert state; and also for using common-anode displays I suppose (with or without external transistors).It should be available on both pin types then, not just the coms?Tim

author: danners430
author_rank: Regular Contributor
timestamp: April 16, 2019, 02:21:57 pm
content: I'm afraid you've completely lost me there...The reason the rows are weaker than the columns is because they only drive a single LED at a time, while the columns are the ones which are cycled, therefore they need to handle greater current.In my case, I wasn't going to use any transistors or anything, just connect the 8x8 matrices directly to the outputs (with resistors on the rows)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2019, 02:30:21 pm
content: Ah. Then use the normal (direct drive) configuration, and P rows and N columns. That should do.Tim

author: danners430
author_rank: Regular Contributor
timestamp: April 16, 2019, 02:33:09 pm
content: Yeah, that's why I think my blonde moment theory was correct!The mode I'm looking for therefore is N-MOS 16COM