stm32H747-Disco Component Size

[Hiram Hyman]

Hi Everyone,

As soon as I learned and successfully transferred data from CM7 to CM4, I bricked my H747-Disco. So, I brought the Disco home from my microscope Lab to place a solder bridge on R192. I realized reading glasses today just doesn't work for me.

So, after unbricking the board and reinstalling the LCD, The unit seemed to be bricked again meaning that it failed to program/connect. Without the LCD, programming both CM7/CM4 was successful. 

After unbricking numerous times, it seemed to be problem with the LCD. I looked under the microscope later and saw that R181 which is right across the street from R192, is missing. The User Manual, UM2411 indicates that R181 (33 Ohm) is for line QSPI_BK2_IO2. Which probably explains why the LCD and Disco no longer works after unbricking.

My question is: I will replace R181 but, I don't know the size of this component. Does anyone now the specifications for this component? This is for QUAD SPI I/O and for what purpose?

Thanks,

Hiram

[Harvey White]

Hardware wise, many times a series resistance is placed in a high speed digital line (SPI, QSPI, FMC).  It tends to compensate for impedance variations on the board on that line, and serves as a bit of a low pass filter.

Measure similar parts in inches.  A 1206 SMT resistor is 0.120 long by 0.060 wide.  Typical sizes are 0805, 0603, and 0402.  Given that the board is assembled by pick and place, a 0402 is likely and can be installed by hand with some care.  The next (inch) size is 0201, which I have never used and will likely never.  Way too small for hand assembly boards.  I can do 0402, but don't like it.  I prefer 0603.  You're talking microscope and very fine soldering tip.  The trick is to either use soldering paste, or to put a tiny bit of solder on one pad.  Put the part over the other pad, melt the solder, and slide the part over into position.  Quickly solder the other end and you're ok.  Remember that these parts *do* conduct heat, and too much heat too long on one side melts the other.  I use temperature controlled irons (Metcal) although Hakko and the like would work as well.

Size above is a guess, but it's based on what they do on boards.

[Tesla DeLorean · Accepted solution]

BOM data should be under the CAD Resources tab on the product page

https://www.st.com/en/evaluation-tools/stm32h747i-disco.html#cad-resources

ST should have put a switch on BOOT0. You have to cycle the power a couple of times to clear the LDO/SMPS issues.

[Hiram Hyman]

Harvey,

Thanks for your response. It is very informative and  something that I must take note of for future designs. For me I prefer 0805. However, in this case it's 402R. I'll follow your advice to place the smallest component I'll have to work with.