Re: HP-15C LE : Workaround for the high current spike Message #3 Posted by Lyuka on 11 Jan 2012, 7:50 p.m., in response to message #2 by uhmgawa
Hi uhmgawa,
The decoupling around the MCU seems good, but it's not the point.
Though it's good for stable power supply, the total amount of the bypassing capacitance is not enough to eliminate the supply voltage drop by the internal resistance of the batteries for 40mA-40us spike.
To make the things worse, it's not the in-rush current, in other words, this spike occurs at every any key presses.
As previously mentioned by Seth Morabito at this thread, the battery voltage depression occurs by high current draw (20mA or so) and the internal resistance rises enough to drop the voltage below 2.0V at the current spike. The high current draw condition occurs at every key press or at calculator is "running", and the voltage recovery time of the CR2032 battery is quite long after such heavy load.
By my quick test, the "Pr-Err" happens after battery voltage drop less than 1.8V or so, at that voltage calculator will shutdown.
Regards,
Lyuka
|