Laszlo Frei

Home built demo board problem

Discussion created by Laszlo Frei on Jul 12, 2010
Latest reply on Jul 24, 2010 by Laszlo Frei



I'm using a MC56F8365 unit for a motor control project. I decided to build my simple, self built demo board according to the 56F8367 evaluation module schematic. The first version had some serious problems because of high current consumption (200mA without any extra peripherals) and had a serious overheat on the voltage regulator . I decided to build a more simple test circuit, connecting only the microcontroller with these part: all the Vdd, Vss pins, OCR_DIS on ground, Vosc on Vdd, CLKMODE on ground, all Vcap pin connected by the proper capacitor, reset with the 74AC00 circuit, 8MHz Crystal with 1M resistor parallel to it...  To generate the 3.3V voltage, I'm using an LD1117-3.3 chip. When I power up the circuit, it consumes around 150mA and the voltage generator(LD1117) is getting seriously overheating( it's maximum current is 800mA)... so I must turn it off... Now I found out that when I disconnect the 8MHz crystal, or disconnect only the parallel 1M resistor, or keep pushing the reset button, the current consumption is falling down to 50mA and the voltage regulator is working properly... It is a very strange symptom.... The circuit is correct, there are no wrong pinout-pin connections, short circuits... The schematic is simple. I've tried another microcontroller, but it is from the same sample package... It seems to me when the clock circuit is working a short circuit comes off inside the microcontroller... 

So what may be the mistake? Did I forget something? Is it normal? Are the microcontrollers refused? I've checked the soldering by x-ray. The controller was never programmed. Please help me!

Thanks in advance: