MAX6950 and MAX6951 are LED display drivers that can drive up to 5 and 8 digits, respectively. They are replacements for older Maxim chips MAX7219 and MAX7221. The new ones use a unique LED display interface with only 9 pins no matter how many digits are driven (1 - 8). The pins have shared functions of driving anodes or common cathodes of the displays.
The functionality of the chip is clearly presented in the data-sheet. On the top of this there are several application notes available from Maxim web site. The IC is supposed to drive LED displays whose all digits have distinct pins. However, it is also possible to use double-digit common cathode displays with the corresponding anodes connected in parallel. The principle is described in AN874 "Using the MAX6950 and the MAX6951 LED Display Drivers with Multiplex Dual-Digit Displays". The circuit below is a practical implementation of this principle for driving a 4-digit LED display.
| Schematic | PCB | |
As it follows from the schematic, one should add 4 diodes to multiplex the display. I used SOT23 versions of BAT54 Schottky diodes having a common cathode. The data is loaded into MAX6950 by using the SPI interface. It is important to note that the bottom exposed pad of MAX6950 should be connected to a large ground area on PCB for cooling, as the IC dissipates a decent amount of heat. The connection can be done with a hot air soldering station. In my layout shown below the IC remains just a bit warm.
| Top view | Bottom view | |
I designed this module for experiments with circuits assembled on a prototyping solderless breadboard. Therefore, all board connections are done by using wires that can be directly stuck into the proto-board. The S, D, and C inputs on the board correspond to the SPI Chip Select, Data in, and Clock, respectively. The module in action can be viewed here. The pins of MAX6950 are connected with the LED display pins so that one can use a built-in 7-segment decoder.
Last modified:Mon, Jan 23, 2023.