----- Original Message ----- From: "phil B" To: "Microcontroller discussion list - Public." Sent: Friday, May 27, 2005 2:54 AM Subject: Re: [PIC] Best Pic for the job > The Fairchild 74HC595 datasheet specs a max current of > 35mA per pin though I wouldn't get anywhere near that > with out a pretty gentle duty cycle. The dip package > has a 600 mW limit, and the SO's is 500 mW. > > I've run a number of tests on it because I was > concerned. With all 8 outputs constantly driving LEDS > at 10 mA for 24 hrs there was very little heat > increase (a couple degrees F) so the 500 mW limit may > be conservative. This was with both Fairchild and ST > parts. Any kind of <100% duty cycle is going to help > here as well. > > One thing to be carefull of is inrush current and > spikes on the clock and serial in pin. I use a 1K > limiter and 100K to ground on both RCLK and SERIN. > > Phil At 10ma the Vol (low output voltage) of the 74HC is probably quite a bit less than 1 volt. So, assuming worst case: 1 V * 10 mA * 8 = 8mW Not much dissipation at all. Bob Ammerman RAm Systems -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist