pin compatible high current version of 74HC595 shift register?

[intellijel]

I am planning to use the dout module to drive an 8 x 8 led matrix.

I will sink the current with a uln2003a but I think I still need higher current sources from the shift registers than the 74hc595 (or 74hct595 for that matter can provide)

The TPIC6595  is the ideal solution but it is not pin for pin compatible (why not??).

Does anyone know of a pin for pin compatible high current version of the 74HC595??

cheers,

    Danjel

[Zossen]

,TPic6C195 ; but not 1:1 pincompatible , just make a adapter from 2 Sockets

[intellijel]

turns out it is not even necessary for me. The rgb leds I got are so efficient that the max current draw from any one colour (at the brightness I need) is only 0.6mA.

The 74HCT595 will provide about 25-30mA max current per pin  I could easily drive a row of leds that is 16 wide (16 x 0.6mA = 9.6mA)

[stryd_one]

The 74HCT595 will provide about 25-30mA max current per pin

bugfight says: with all going at once max power for chip indicates 18.5 by my calc

[intellijel]

bugfight says: with all going at once max power for chip indicates 18.5 by my calc

You mean for the SR driving the cathodes and this is only for a duo color

What I mean above is just for driving anodes.

However if I use the 4x16 configuration, each 74HC595 SR is only driving a max of 4 anodes (4 x 0.6mA) but the cathode SR is sinking a max of 24 leds (3 colors x 8 leds per column = 24x0.6mA). As I mention in another post this is well below the current handling capabilties of the uln2003a (assuming it is there to sink current)

[stryd_one]

We were just talking about the 595's capabilities, it's irrelevant of application.

[intellijel]

I am talking about the 74HCT595 not the 74HC595 (it is the higher current version)

[stryd_one]

Nah HCT is the TTL level capable version...

[intellijel]

hmm I misread the datasheets before.

I also assumed this because of what Ralf Suckow said on his page

To support this current, 74HCT595N are used instead of the standard 74HC595.

http://www.suckow.de/ralf/ledmatrix4x20/

In fact I can't see what the difference is at all (except that they are more expensive).

Eitherway, is not the max source current +/25mA?

IO output source or sink current VO = -0.5 V to VCC + 0.5 V

Q7’ standard output - ±25 mA

Qn bus driver outputs - ±35 mA

or is that the total possible for the chip (not individual pins)

[bugfight]

...

Eitherway, is not the max source current +/25mA?

...

i calculated 18.75mA based on max power for the chip (750mW according to ti)

this may not be a good way to calculate the current limit.

wilba pointed out that max current at the power pins is listed at 70mA.  though i don't think this translates exactly to the current at the outputs when they are pulsing, it still suggests a lower limit.

SmashTV did some tests that seemed to support the ~18mA calc

(even running it at 2A for 5 secs before letting out the magic smoke)

i'm sure some folks here are using more than that with high current leds, these ratings usually have a little headroom...

[stryd_one]

In fact I can't see what the difference is at all (except that they are more expensive).

74LS* is TTL levels

74HC* is CMOS levels

74HCT* is cross-compatible with both

http://www.kpsec.freeuk.com/components/ic.htm#logic

There's lots of googling to be had on this subject. I found one really good page that showed which types were compatible with which (about 10 types all up).... of course I can't find it now :(

[stryd_one]

http://www.eng.yale.edu/ee-labs/morse/compo/logic.html Found. FF3 Library is awesome.