How hot should a PIC get? - Page 1
Forum section: electronics / general

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 24, 2011, 06:42:44 am
content: I've got a PIC32 in a current project, and the things is getting rather toasty. Like 45'C when measured with a thermocouple toasty. The thing is running at 80MHz, but I've ran other PIC32's before at this speed and they've never gotten this warm. The chip works perfectly fine, no problems it all. I checked all the pins connections too and they all look good.The only thing I can think of is that I've got some unused pins that are connected directly to ground. I know you're suppose to use pull down or pull up resistors for this but I didn't have the board space. I've got all unused pins set as outputs and pulled low. I've tried setting all pins as inputs (TRISx = 1) and it didn't seem to make any difference.

author: tyblu
author_rank: Frequent Contributor
timestamp: January 24, 2011, 07:18:42 am
content: So, it's sucking current like a hog? How much?

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: January 24, 2011, 07:20:28 am
content: Quote from: TopherTheME on January 24, 2011, 06:42:44 amPulledlow? Pulled low via a resistor or connected to ground directly? Are the outputs set low?

author: PeterG
author_rank: Frequent Contributor
timestamp: January 24, 2011, 08:35:35 am
content: Sounds to me you have one of the grounded outputs set to logic hi, without a current limiting resistor on the output the mcu will get warmer than usual.Just my 2 cents

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 24, 2011, 09:40:51 am
content: Unused pins should either be set as outputs and left unconnected, or as inputs and tied high or low. The former is preferable as it give you the option to use pins for debug outputs or modifications.The latter would normally only be used for input-only pins, or where you want to tie them for pcb layout reasons.

author: CafeLogic
author_rank: Regular Contributor
timestamp: January 24, 2011, 11:48:43 am
content: Quote from: TopherTheME on January 24, 2011, 06:42:44 amThis could be normal it depends what you have going on and which PIC32 it is. With the new ones (575/675/775), you should expect about 10C over ambient without having any peripherals enabled. Junction to ambient is 47 c/W (64-pin tqfp) so do the math with your chip. Double check your clock settings, the PIC32 could function up to 160Mhz but obviously will use twice the current. A good way is to check is to set the clock at a low rate with the internal OSC and see if the problem clears. Here are some settings that I have verified set it at 20Mhz with the internal oscillator.Code:#pragma config POSCMOD = HS, OSCIOFNC = OFF, FNOSC = PRIPLL, FPLLMUL = MUL_20, FPLLODIV = DIV_4, FPLLIDIV = DIV_2When you start up a PIC32, by default, you do not have control of all of the pins (I hate that shit, if I want a periph, ill enable it). Here is some code that will give you control of all the pins.Code:DDPCON = 1;CVRCON = 0x0000;AD1PCFG = 0xFFFF;U1OTGCON = 0b00000100;U1PWRC = 0;ETHCON1 = 0;You might need to comment some of those like ETHCON if you aren't using an Ethernet version. Pins G2 and G3 are input only.

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 24, 2011, 04:04:47 pm
content: Quote from: Jon Chandler on January 24, 2011, 07:20:28 amThey are just connected to ground directly and all the unused pins are set as inputs.I think the chip itself might be damaged. I've got a PIC32 on a breadboard that I wired up in a very similar manner and its temp is about 19'C (its about 17'C ambient).

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2011, 06:26:12 pm
content: I'm a bit new to PICs myself but from what I've heard unused pins should be configured as inputs and connected to either +V or 0V via resistors in case they're accidentally configured as outputs which should never be directly connected to either power supply rail. Some PICs have built-in pull-ups so you could use them to tie the pins to +V if you want to save space.

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 25, 2011, 05:42:04 pm
content: I tried drilling out the back side of the via's that were tying the unused pins to ground and saw no change. Then, the I2C and SPI peripherals stopped working and the chip started getting even hotter. So I replaced the chip and now everything works perfectly and the chip doesn't go 4'C above ambient when running at 80MHz. I guess the original one was damaged/defective.

author: tyblu
author_rank: Frequent Contributor
timestamp: January 26, 2011, 07:13:54 am
content: I was a perfectly functional one-time self-reflow unit.