what happens if 5volt logic (microprocessor) is powered with 3.5 volt?

3 volt logic can take upto 3.6 volt...

now if the difference is too big, a rectifier is formed and the lower voltage device can be destroyed.

who has experience with such circuits?

if not, i know a way how to shift the level, but it requires additional components.

ideas HOW much the 3 volt circuit will consume if it gets 4 volt?

and the minimum voltage for 5 volt microprocessors?

anyone has a board (not PIC), and can power it with 4volt, 3.5 volt, 3volt?

i have tried a PIC with 3volt, even 2.4 volt, where it did not startup immediately, but sometimes it worked with 2.4 volts.

actually i would like to know if i can avoid the shift circuit. probably i can try it myself, because the low-voltage part is the RAM chips, and i can run the system by ROM, then try to power it by 3.5 volts.

the documentation does not explicitly state a minimum voltage for the processor, probably it needs 5 volt all the time.

there is also a 3.3 volt version, but the one i have is a 5 volt version, and is not listed in the 3.3 volt table.

probably it will work with 3.5/4 volts?
Posted on 2005-04-02 07:34:21 by akidd86

the documentation does not explicitly state a minimum voltage for the processor, probably it needs 5 volt all the time.

there is also a 3.3 volt version, but the one i have is a 5 volt version, and is not listed in the 3.3 volt table.

probably it will work with 3.5/4 volts?

Huh? Are you looking at a product list? The data sheets are what you need. They will tell you what the minimum and maximum are. Go to the Microchip web site and hunt down the data sheet for your PIC.
Posted on 2005-04-03 04:18:11 by tenkey
thank you for the reply. the documentation (datasheet) does NOT state an explicit minimum voltage.

as mentioned, i have operated PIC (5v) with 2.4 volt (at 32khz)

now, the microprocessor/ROM operates by 5v, the RAM by 3v.

the question is for users who have a microprocessor system and can try to operate it with 4volt/3.5volt.

the system also includes a PIC.

i am looking for real experience with shift circuit/ operating below recommended voltage.

for further replies please notice i am going to assemble the system on my own.
Posted on 2005-04-03 06:35:00 by akidd86
The problem you may have is reliability.  Most ICs have a tolerance of 5% voltage swing though it could be more, I don't recall.  Reliability will be affected by noise in your system.  There won't be enough headroom.  Should there be noise on the line, or any voltage fluctuation, a 0 might get interpreted as a 1, and vice versa.

Yes, you might get this to work but whether it works consistently or not is the key.
Posted on 2005-04-03 12:15:32 by drhowarddrfine
i understand, the headroom gets smaller. however, i use to integrate ceramic condensators (induction free- fast response to drop-down spikes).

but i have not seen the circuit goes into a module slot of a system, which operates with 5 volt.

so the microprocessor/ROM has to be powered with 5 volt.

what happens if i power 3 volt RAM with 5 volt ?

does it consume more power, or do i have to fear latch up? the documentation specifies upto 3.6 volt as safe.
Posted on 2005-04-04 09:53:38 by akidd86
first, you should take a look on another datasheets that mention the vcc voltage range (i.e. your uprocessor or ttl chips).

second, i can not tell that powering 5V device with 3.x V would make it okay. it "might" be, but increasing devices utilized by system would make it ruined.
even for single MCU system and couple ttl chip, it won't work with those 3.x V.

there is app note that describe these thing.
Posted on 2005-04-08 02:56:01 by dion
what happens if i power 3 volt RAM with 5 volt ?

Smoke. Maybe lots of smoke. Possibility of sparks and flames too.

Don't do it, peroid. If the chip was meant to run at 3 volts, run it at 3 volts. The manu's data sheets are to be followed explicitly. Completely.

No exceptions.

It *might* run at 5 volts, or seem to. Then purchasing finds an equivalent part, same specs, different manufacturer. THAT one doesn't work, and you're left trying to explain why you ran a part outside of the specfied limits.

And why 5,000 production units are in final test awaiting rework.

Run 5 volt stuff on 5 volts. Run 3 volt stuff on no less then 48 VAC... oops, make that THREE volts.

If you need to interconnect 5V and 3V logic, thats not too uncommon these days, and several manufacturers make level converters for logic lines. Use em!

Posted on 2005-04-08 14:35:46 by Ernie
  A method I have used is to feed power to the memory through one or two doides like '914s. The memory is usualy 3.3 volts and does have a tolerance spec.
Posted on 2005-04-11 10:12:59 by mrgone
thank you for your replies.

now, here a list of existing things
-microprocessor                5v there is a revision which works on 3.3v
-RAM 256Kbyte                3.3v
-FLASH ROM 128Kbyte      5v

documentation for all these items. obviously, writing programming tools for the processor, i read them.

now, 3.3v memory works, if they get to 4.3/3.6 volts?

the problem is they get 5v from the processor side, and may latch up someday. i have read if logic gets higher voltage than supply, this may occur. probably the microprocessor works by 4.3 volts?

probably the latch up increases the power consumption a little, 50mA instead of 20mA. this would be allright. can you measure the consumption, and compare to value in the datasheet?

in addition, i figured out how to shift logic level using jfet transistors. now, i have 50 of them around, thought it would be 2MByte, but the memory chips are only 2MBit.

however, 1/4 size of DIL, somehow tricky to solder them in. even the processor (1/2 DIL) was not that easy: i had to bend the pins into flatpack format, previously it was PLCC. have done this yesterday, Vcc/GND connected.

for the small memory chips, i use to bend the pins U/D alternating, this gets 1/2 DIL. looks i am getting two small spiders.

anyone reading this, it goes into a module port (sega console), and the port has 5 volts. 3 voltages (5 volt, 4.3 volt, 3.6 volt) and no guarantee it works, or around 36 transistors. they require pull-up resistors, and i have not spend time figuring out the required value. it must be less enough to charge the bus gate capacity, which would be around 100pF. clock is 12MHz but it does not change each cycle. if the value is too small, let's say 1k, it increases power consumption remarkable. don't know how much the gates can pull down, guess it is 2mA or something.

the design is tricky, because memory area's are shared by three different microprocessors.

if you have any hints for the power supply...
Posted on 2005-08-18 05:25:26 by akidd86