8-bit Microcontrollers中的主题 excessive current consumption

excessive current consumption

leslie — Tue, 12 Aug 2014 18:54:21 GMT

Hi,

Does anybody have an idea why an otherwise working MC68HC908JL8 would consume around 100mA? Of course it heats up, of course it sucks the juice out of the power supply...

I am using it with RC oscillator, the freq is correct.

It happens almost 50% of the 40 pieces I tried by now.

Pulling down RST will stop the over-current, even if the (test) program only has configuration.

Changing the controller USUALLY does not solve the problem.

I use them in another product where they perform wonderfully. There I use 3.3V supply; the failing ones get 5V.

It could also be a PCB layout issue, as the 5V regulator is about 7" away from the controller. The supply traces are wide with no loop; everybody got their own .1uF near the supply pins.

Running out of options/time.

Re: excessive current consumption

Encoder1 — Fri, 22 Aug 2014 10:30:08 GMT

Hi Laszlo

Your problem may depend on some unused pins incorrectly declared as outputs which were tied to ground or Vcc. This is quite a common issue.

Hoping it can be useful,

Salvatore.

Re: excessive current consumption

dougpaulsen — Fri, 22 Aug 2014 10:46:31 GMT

Just a real long shot, but are you using PLL to bump up your clocks? If so, try a simple test program with and without using PLL and check you consumption. We've just discovered PLL uses 3-4 times the published current numbers (but that's on another micro).

Re: excessive current consumption

leslie — Thu, 28 Aug 2014 17:02:52 GMT

Thanks for the short and long shots...

I found an errata showing that the mask set was screwed up. The OSC2 pin is not used in RC mode, and functions only as output (I needed it as input). I had to force it to LO, otherwise it draws extreme amount of current. The errata does not say it though:

I/O Port Function on OSC2/RCCLK/PTA6/KBI6 Pin SE65-IO_PORT

An anomaly has been found with the OSC2/RCCLK/PTA6/KBI6 pin when:

• RC oscillator option is selected (OSCSEL = 0) and the pin is selected as

PTA6 (PTA6EN = 1).

Under this condition, the PTA6 pin can only function as an output pin;

not an input/output pin as stated in the device data sheet.

Because PTA6 is output only:

• The DDRA6 bit has no effect on PTA6.

• The PTAPUE6 bit must not be set to logic 1 to avoid possible current

drain if DDRA6 is logic 0.

• The KBIE6 bit has no effect, as keyboard interrupt, KBI6, is not

available.

To maintain compatibility with future silicon, the DDRA6 bit should be set to a

logic 1 if PTA6 is used as an output port pin.

Strangely during HW reset, the current was minimal.

I'll have to live without this input.

Now I can flag this as "answered". Thank you.