Can the STP16C596 output 40mA per pin at 7V with the Arduino?

I am trying to make a display that shows voltage, current, and watts in 7 segment displays. Each variable will be displayed with 4 seven segment displays (with decimal), so there will be a total of 12 7 segs. I can't use LCD because it needs to be visible in the dark. I wrote some code that I haven't tried running yet (but I did debug it) that will measure voltage and current, and calculate amps. Also in the code, it rounds to accommodate 4 digits and a decimal, and it will send it out in a serial sort of format I made for 595 shift registers.

This would have worked great except for the fact that the 595 can't source enough current for my application. It turns out I need 40 mA per segment, and each segment has a voltage drop of 6.8V! (I'm using 4" 7 seg displays) I was going to use transistors to make this work, but then I saw the STP16C596, which says it can source 120mA, but my question is: Is that per output pin, or total? Also, can I get the outputs to output greater than 5V when using an arduino, or does that require the input to be greater than 5V. I also can supply this chip and the 7 segs with another power supply, that's no problem.

Thanks in advance

P.S. I'm sorry if I have broken some forum etiquette, or if I posted this in an incorrect way, I'm new to forums.

The supply voltage is maximum 7V -- that's the voltage needed to drive the logic in the chip. The output pins, however, allow up to 16V. Total current is limited to 1920ma so that would be all 16 pins driving their maximum 120ma. These values are all listed in Table 4 of the datasheet.

Note that the STP16C596 sinks current. The cathode side of the LEDs would be connected to the "output" pins of the IC and the anode side connects to (up to) 16V. The VDD pin on the IC requires 5V (typical).

I have a very similar project underway. The STP16C596 have identical pinouts to my TLC5925 so the circuit shown there might provide you with some help.

The supply voltage is maximum 7V -- that's the voltage needed to drive the logic in the chip.

Don't try an drive the chip at that voltage, just use 5V.

The chip doesn't source current it sinks it. So it doesn't output a voltage, its outputs pull current through the device. The ammount of current it pulls is set by the single R-EXT resistor.
Yes it will handle 40mA per pin but it will not supply the current but sink it.

Thanks for the prompt replies, bros! And sorry for my noobiness, sink, not output. I do see that the total output current is 1920mA, so that is good news there, thanks for that intel. The only thing I'm still skeptical of is using one external resistor to control the current for all of the pins. Sure that would make sense if I was running one segment at a time, but if all of the segments were running, that would be too much resistance. So wouldn't I need to hook up that external resistor pin to ground, and use individual resistors for each segment, or is there some black magic I'm not understanding here.

The one resistor sets a voltage value inside the chip, that the chip uses to control all the constant current outputs. It is the way the chip works, don't worry too much about how it works at this stage just rest assured that it does.

or is there some black magic I'm not understanding here.

Yes it's magic, each output bit is individually constant current controlled. I used two equivalent chips from another manufacture and wired them is series to form a 32 bit shift register to drive a 5x5x5 LED cube. These kind of driver chips made the hardware part of the project a breeze to build and debug. They cost a little more but the savings in other components and board space makes them a bargain.

Lefty

Oh, neato, that will work perfectly! I know I don't need to know all of the inner workings of this IC to get this to work, but I am curious. If the IC doesn't output voltage from it's output pins, and they are just sinks, why does it say up to 16V output voltage? Also, I just found out it's no longer available, so now I'm looking for a newer version. I looked into the TLC5925 that you used, Chagrin, but I am actually designing this for a customer to use (I work at an electronic components retail store) and he will be handling it and assembling it. This dude is a super noob with hardware, so I'd like to steer clear of SMD if possible. It looked like the TLC5925 is only SMD.

So I'm going to do some serious googling for a 16 bit shift register with constant current, but it might save me some time if you guys knew a part number for one in stock. Does anyone have any suggestions?

Destate9:
I can't use LCD because it needs to be visible in the dark.

What about an LCD with a backlight?

Destate9:
Oh, neato, that will work perfectly! I know I don't need to know all of the inner workings of this IC to get this to work, but I am curious. If the IC doesn't output voltage from it's output pins, and they are just sinks, why does it say up to 16V output voltage?

Just nomenclature. I wouldn't worry about that.

Destate9:
Also, I just found out it's no longer available, so now I'm looking for a newer version. I looked into the TLC5925 that you used, Chagrin, but I am actually designing this for a customer to use (I work at an electronic components retail store) and he will be handling it and assembling it. This dude is a super noob with hardware, so I'd like to steer clear of SMD if possible. It looked like the TLC5925 is only SMD.

Checking newark.com for DIP cases and the same type of interface as your STP16C596, for 16 outputs there's the MAX6971 and for 8 outputs The TLC5916/TLC5917. I'm sure Mouser or Digikey would have additional options; they will probably be described as a "LED driver" as they are on Newark.

If the IC doesn't output voltage from it's output pins, and they are just sinks, why does it say up to 16V output voltage?

Because that is the maximum voltage you can apply to the anode of the LED, while the cathode is being dragged down to ground by the chip. Any more and the leakage through the LED when the chip is not pulling it to ground (that is when the LED is off) would be enough to zap the chip.

I assumed he was confused as to why it's called an "output" instead of an "input".

Yes but it IS an output pin not an input pin.

Just because the pin sinks current doesn't make it an input.

The term input refers to a signal carrying information into a system, output refers to a signal being used to control some circuitry outside the system.

Often data sheets are written by people without a good grasp of English.

Alright, so if I'm understanding correctly, the output voltage is the max voltage you can have at any output pin? So if a segment has a voltage drop of 6.2V, I could supply each segment with up to 22.2V, or 16V? Because it would make sense to me if there was a max voltage the mosfets (or whatever this thing uses) could take from source to drain. That would also lead me to believe the Max voltage output rating would be for the voltage between the segment and the output pin, not the power source for the segments. Also, I found the MAX6969 (http://pdfserv.maxim-ic.com/en/ds/MAX6969.pdf) which looks like it will work for this application. It has a lower voltage input, lower max voltage output, and lower max current, but that should work, right?

Oh, and I already ran that backlit LCD idea by my customer. He would prefer the 7 segments, but thanks for the suggestion.

So if a segment has a voltage drop of 6.2V, I could supply each segment with up to 22.2V

You might reasonably think so but you would be wrong.
The segment only has a volt drop, in this case 6.2V when it is on and conducting current. When it is off there is a small leakage current that lets the full voltage that is applied to the other end go straight through the device. So that supply voltage appears on the output, therefore if the chip says it is 16V then it is 16V maximum to apply to the other end of the display. Note you can use any voltage up to 16V, if your display takes 6.2V then I would say 6.8V is the minimum you could use.

As to the MAX6969 this will not work for you because your display needs 6.2V and the maximum you can apply is 5.5V.

Grumpy_Mike:
As to the MAX6969 this will not work for you because your display needs 6.2V and the maximum you can apply is 5.5V.

Not to mention it's the most expensive shift register on the planet. $8.36 at Mouser and $8.61 at DigiKey.

Perhaps I'm missing something, but why has nobody mentioned the TLC5940 LED driver as a replacement for the STP16C596?

Whatever driver chip you use, you need to be mindful of the total power dissipation of the chip. For example, if you sink 40mA from all outputs and the supply voltage less the voltage dropped by the LED is 2v, that's 40 x 16 x 2 = 1280 mW.