Post by thread:Q:Current drawn by the 16C65

Hi, I'm trying to make an application with the PIC where the current drawn by the system is important (should be as small as possible). In that regard, I've been looking through the 16cxx datasheets, and I have found several values for the current drawn. One place (16.0 Electrical Characteristics for PIC16C65) it states: Maximum current out of Vss pin 300 mA Maximum current into Vdd pin 250 mA while a bit later it states that the max Supply Current is 5 mA Now which one of these is the current that the PIC actually draws? It seems likely that the first (huge!) number is the max that the chip tolerates without being damaged, while the other (much nicer) number is the amout it actually draws. Am I right in this? Has anybody tested this? If anybody knows, please drop me a line. Thanks in advance. Hans-Christian Prytz spam_OUThanscprTakeThisOuTlogin.eunet.no

hanscpr@LOGIN.EUNET.NO <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> wrote: > It seems likely that the first (huge!) number is the max that > the chip tolerates without being damaged, while the other (much > nicer) number is the amout it actually draws. Am I right in this? Yes. -Andy Andrew Warren - fastfwdKILLspamix.netcom.com Fast Forward Engineering, Vista, California http://www.geocities.com/SiliconValley/2499

> Hi, I'm trying to make an application with the PIC where the > current drawn by the system is important (should be as small as > possible). > Maximum current out of Vss pin 300 mA > Maximum current into Vdd pin 250 mA > while a bit later it states that the max Supply Current is 5 mA > > Now which one of these is the current that the PIC actually > draws? The 5mA figure is the total amount of current which will be used internally by the device. The 300mA figure is 5mA [internal current usage] greater than the maximum total current that may safely be sunk via the port pins [if you sink a 20mA LED, that 20mA will have to go out the ground wire] and the 250mA figure is 5mA greater than the maximum total current that may be safely sourced via the port pins. To put it another way, if you run the chip with nothing connected, it will draw 5mA [or less]. If you run it with 12 LED's sourcing 20mA each, it will draw 245mA.

>To put it another way, if you run the chip with nothing connected, it will >draw 5mA [or less]. If you run it with 12 LED's sourcing 20mA each, it will >draw 245mA. Hi, I didn't realise you could source so much current from a 16C65. Is the same true for a 16C84. My application uses 3 solenoids which pull 90 mA max. I use 3 darlingtons to switch them; since space is at an absolute premium, could I dispense with the darlingtions and drive the solenoids direct from the port pins? Geoff.

> > >To put it another way, if you run the chip with nothing connected, it will > >draw 5mA [or less]. If you run it with 12 LED's sourcing 20mA each, it will > >draw 245mA. > > Hi, > > I didn't realise you could source so much current from a 16C65. Is > the same true for a 16C84. My application uses 3 solenoids which pull 90 > mA max. I use 3 darlingtons to switch them; since space is at an absolute > premium, could I dispense with the darlingtions and drive the solenoids > direct from the port pins? The 16C84 is listed my data book with the following specs: Max Vss current: 150mA Max VDD current: 100mA Input/output clamp current: 20mA Output current sunk, per pin: 25mA Output current sourced, per pin: 20mA Output current sunk, total of PA0-PA4: 80mA Output current sourced, total of PA0-PA4: 50mA Output current sunk, total of PB0-PB7: 150mA [same as device limit] Output current sourced, total of PB0-PB7: 100mA [same as device limit] Total power dissipation: 800mW When you say your solenoids need 90mA max, is that each or is that total? Will more than one be on at once? If the 90mA is a total figure and each solenoid only requires 30mA, you should be able to simply sink them off port B, using two output pins each. Otherwise, if 80mA each is enough, but you only need one at a time, you could wire the solenoids in a "triangle" with one vertex tied to PA0-PA3, one vertex to PB0-PB3, and the last to PB4-PB7. Then you could activate the solenoids as follows: Sol #. PA0-PA3 PB0-PB3 PB4-PB7 1 Sink Source Off 2 Sink Off Source 3 Off Sink Source Of course, then you only have one I/O port available for communicating with the outside world, but such is life. PS--Be *VERY* careful to ensure that you control any back-EMF from the solenoids. Solenoids can produce massive voltage spikes if not dealt with properly.