PIC18F4580 low power mode

[vikraml]

Hi all,

I am using the PIC18F4580 in a battery powered application, to basically implement a timer circuit. I am using timer1 (external oscillator running at 32.768khz) on the PIC to wake the microcontroller from sleep mode.

My circuit at present consumes around 7mA of current, 3mA for an led and the remaining 3-4mA is cosumed by the microcontroller when the Timer1 circuit is turned on. When the microcontroller is in sleep mode and timer1 is turned off it consumes roughly 1mA.

Is there some way I can reduce the amount of current cosumed by timer1 circuit.

Any other suggestions on how I can reduce the amount of current will be appreciated.

Thanks

[Ttelmah]

1mA, is a lot more than it should be drawing.
What are you using for a voltage regulator (lots of these, have quiescent currents dozens of times that of the PIC). Are you making sure that no pins are 'floating' when in sleep mode (either run them as outputs, or ensure there is a large resistor providing a tiny bias current)?. Have you switched off the peripherals (ADC etc.)?. Are you using the watchdog?.
What clock rate are you running when awake?. Seriously, I have battery powered systems, using the same device, and my _running_ current is below 1mA. The sleep current is typically under 1/100th of this...
The timer, should not use 3mA.
What voltage are you running?. What clock rate when 'awake'?.

Best Wishes

[vikraml]

Thanks for your response. I am using a MAX603 LDO 5V regulator . The primary oscillator is a 4MHZ crystal. Before the PIC goes into sleep mode I turn off all the peripherals except timer1 and I am not using the watchdog timer.
Timer1 clk is configured to be device clk when the PIC wakes up from sleep mode. (T1CON = 0xCF).

what do you suggest for the I/O's during sleep mode. Should they be setup as inputs or outputs (high or low).

Thks

[vikraml]

Hi all,

After trying everything possible to reduce the extra 8mA my board is consuming, I stumbled upon something that I was overlooking. On my board I have eight 7-segment Common cathode displays that are driven by a MAX6951 (LED driver). When the microcontroller is in low-power/sleep mode all the external peripherals(i.e led-driver,displays)are in shutdown mode. But for some reason these displays still cosume current around 1mA each (which adds up to 8mA).

Can anyone shed some light on this, I don't completely understand why it would do that.

Thanks

[Ttelmah]

One thing leaps to mind. The shutdown consumption of the driver, is only warranted if all it's logic inputs are pulled to 0v, or up to 5v. You might want to try turning off the SPI peripheral, and manually driving these lines high, before sleeping.

Best Wishes