The datasheet says 100mA max, but the 324P says 200mA max - 100mA seems pretty low.
324PB max gnd and vcc current...
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On the -AU package, the ground pin 18 and 39 (324p) turned into TX2 and SCL1. While the VCC pins 17 and 38 turned into RX2 and SDA1.
I had not noticed that 100mA max ratting, but I do like all the IO pins on that chip. My project is not doing much current sourcing or sinking so I should be safe, but oops I should have looked at that.
Watch if you doing analog readings using Vcc as ref, since at high currents there can be a small offset. The reduced quantity of power pins could certainly require a lower limit.
I'm trying to find a 44 pin mega suitable for driving some LED displays. I noticed the mega162 allows up to 400mA! Are there others like the mega162 that offer this much?
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mega4809, 48 pins, 2 VDD-GND pairs and 1 AVDD-GND pair, UQFN has a pad to sink the heat into the PCB
ATMEGA4809 - 8-bit AVR Microcontrollers - Microcontrollers and Processors
If room on the PCB, a complementary pair of bipolar transistors will current gain.
NSS40302PD: Low V<sub>CE(sat)</sub> Transistor, Complementary, 40 V, 6.0 A
The 4809 is interesting, it talks about the current per pin on the VCC and GND pins unlike older datasheets - or did other datasheets mean per VCC and GND pin or for all of them?
What you are thinking with the transistors? (I'm not following you...)
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alank2 wrote:
I don't know.
or did other datasheets mean per VCC and GND pin or for all of them?
alank2 wrote:
What you are thinking with the transistors?
TND6093 - Low VCE(sat) BJT's in Automotive Applications
(page 4)
though there's
Figure 2. Large LED Array using a Logic Gate to Control the Low VCE(sat) BJT Switch
on page 3.
NSS40302PD: Low V<sub>CE(sat)</sub> Transistor, Complementary, 40 V, 6.0 A
In the old days, driving to gnd was better. Nowadays, these drivers apparently are well-matched complementary pairs (at 15ma, you lose a volt both at gnd & at Vcc). They mention 100-200ma per group....how much current do you need? Lots of low current LED's these days.
Looking to drive four LTP-305's (5x7 led matrix). There are either 20 or 24 columns depending on whether I support the crazy little decimal point in its own column. 7 rows. While each LED can tolerate 10mA continuous, I can't even begin to imagine how bright that would be. I am looking at 12.5mA at 1/7th duty cycle (14.3%) which will give an average of 1.785mA per LED. 12.5mA * 20 columns is 250mA and I plan to use some line level mosfets to switch the rows and drive the columns from the AVR (if that is workable...).
The 4809 is interesting, it talks about the current per pin on the VCC and GND pins unlike older datasheets
Hi Alan,
You probably already know this, but I'll mention it just in case...
In many of the "old" data sheets the current limits were listed in the --> Footnotes <-- , below the electrical spec data information (boxes).
So you really had to look closely to find it.
The extra kicker, also, is that for the old chips at least, the current limits were spec'd for BOTH the power pins, and for combinations of I/O pins, (sometimes a full port, sometimes pin combinations split across several ports).
JC
Edit:
OK, having looked at the new data sheet...
There is one Vcc/Gnd and one AVcc/AGnd pair of pins.
Imax is 100 mA on the power pins, AND on the individual port combinations, as listed in the "Note" Footnote, in the Electrical Characteristics.
I would interpret that liberally, meaning that the digital supply pins can carry 100 mA, max, and that the analog supply pins can carry 100 mA, max.
BUT, it doesn't come out and directly say that.
If it matters for your design, then I'd definitely eMail Tech Support for clarification, (or confirmation), as to what the current limits are for the total chip, (i.e. 100 mA on both the digital and 100 mA on the analog supply pins, simultaneously, or just 100 mA on the chip, in total).
The 200 mA to 100 mA change is likely do to the die change when they changed the fabrication and made the guts of the chip smaller.
JC
Last Edited: Tue. Aug 13, 2019 - 03:58 PM
JC - I did find that and it is certainly "limiting"! I noticed that section was missing from the 4809 datasheet unless I missed it.
I'm conservative.
And I don't like a hardware design that can fry the hardware if there would happen to be a software bug, (during development), or glitch, (real world usage).
If the multiplexing software locked up, or the software otherwise enabled "too many" LEDs at once, it could fry the micro... as your I/O drive lines won't have individual current monitoring and clamping / rollback.
That is sometimes the case with high pulse powered, multiplexed, LED drivers...
So just be very careful as you write your software.
It might be reasonable to put a higher value current limiting resistor in the circuit while you do your design work.
If you put a string of NFets or PFets or whatever between the micro and the LEDs then you totally eliminate the possibility of over current destroying your micro.
In this case the issue becomes the power supply current capability, and the power supply, and the power wiring, can be protected with a Fuse, or with some other current limiting device, or active circuitry.
I don't know the model number for transistor arrays, with a bunch of them in one easy to use chip, but I am sure there are many available in numerous configuration and current capability versions.
JC
I use a P/N pair in a 5 pin sot-753 package to drive a P-Fet switch, would work as well with an N-Fet too, here is the Digikey part number: DME201010RCT-ND
Jim
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alank2 wrote:
or low Vce-sat bipolar transistors (greatly increased current gain at saturation versus typical)
... and I plan to use some line level mosfets to switch the rows and drive the columns from the AVR (if that is workable...).
TND6093 - Low VCE(sat) BJT's in Automotive Applications
(page 3)
...
though MOSFETs continue to improve.
A new arrival at Mouser on 22-Jul'19; these can be driven, with margin, by a 3V MCU :
Low-Gate Drive Voltage MOSFETs - ROHM | Mouser
edit :
NSS60201L: Low V<sub>CE(sat)</sub> Transistor, NPN, 60 V, 4.0 A, SOT-23 Package
NSI45025A: LED Driver, Constant Current Regulator, 25 mA, 45 V
Last Edited: Tue. Aug 13, 2019 - 05:23 PM
The 324PB is like 328PB made on a newer proces (best know as those where the high power osc. don't work).
Those chips are for toy and hobby, avoid using them professionally then use the real parts.
I still find it bad that they used the same numbers (normally the extra letter means an improved chip).
And the really bad part was that they tried to make a 328P on the same proces, (went so far that there was a datasheet).
thank god that that didn't happen.
DocJC wrote:
I'm conservative.
And I don't like a hardware design that can fry the hardware if there would happen to be a software bug, (during development), or glitch, (real world usage).
If the multiplexing software locked up, or the software otherwise enabled "too many" LEDs at once, it could fry the micro... as your I/O drive lines won't have individual current monitoring and clamping / rollback.
You are smart to do so DocJC! I think there are some pulse applications where you have to go above the continuous rate to get the brightness you want. Whenever I am doing multiplexing like this I always use a watchdog and make it reset if the ISR that rotates the row isn't running. Still, I'm not that far from 10mA anyway that I couldn't drop from 12.5 down to 10 and play it safer.
Also remember that the 100mA is GND and VCC pins but when you have a IO load, the power only run thru one of the pins :)
So you can sink 100mA and source 100mA, so do some homework before you make the PCB ;)
In the 48-pin-Data-Sheet-megaAVR-0-series-DS40002016B.pdf datasheet, on page 6 where it shows the pin layout, it has a legend for GPIO on VDD power domain, and GPIO on AVDD power domain. Can you see which pins are related with which VCC/GND pins using this? Or perhaps I am missing it. Which GPIO's connect VDD pin 42, which VDD pin 14, which AVDD pin 28. It looks like you can see the AVDD pins because there is only one AVDD. Is there somewhere else it shows which VDD the other pins are connected to?
Just to add a bit of noise to this...
The Mega329P data sheet, in the Absolute Maximum Ratings section at the very start of the Electrical Characteristics chapter says 40mA absolute maximum DC current for any IO pin and 200mA maximum DC current for Vcc and Ground pins. This limit is INDEPENDENT of package.
Now, as pointed out above, this is quite unclear as to whether you can do 200mA through EACH Vcc or Ground pin, there being more than one of each, or whether that is the total Vcc or Ground current. My take on it is that YOU have no control over the proportioning of the currents between the Vcc and Ground pins. Thus, the pragmatic designer ought to conclude that this refers to the TOTAL Vcc current and the TOTAL Ground current.
Of course, since M328P is not being considered, then take it as a (possibly) amusing side note.
Jim
'328, '329 -- whatever it takes.
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'328, '329 -- whatever it takes.
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