ProtoDAC TDA1387 X8 project

[OnkelPH]

[quote='hifinet' pid='52043' dateline='1707499051']
Do you mean getting the 5V from the pin 2 and/or 4 of the RPi GPIO? I don't think the voltage differential will be enough. The voltages are usually less than 5.1V, and that is right on the margin of the dropout voltage of the LT1963 to get 5.0V with the current draw of ProtoDAC. You will need at least a 100mV differential. If the voltage differential is less than indicated in the chart on page 1 of the datasheet, the LT1963 won't regulate.

Thanks, so I can get 5v from pin 2/4, but LT1963 will most likely not work. Understand.

The way it could be done is to change one of the resistors on the board. See the adjustable regulator Figure 2 on page 14 of the datasheet. Just omit Iadj * R2 to simplify, because Iadj is only 3 microamps. The two resistors setup the voltage of the regulator. They have online calculators for the LM317 which will get you very close.  Instead of having it regulate to 5.0V, you could change one of the resistors, and have it regulate at 4.7V instead, for example. The resistors can be changed by removing them or adding a resistor in parallel, to decrease the resistance slightly. On this board, they are SMD which are hard to solder. They do make some LT1963 boards that use through hole resistors.

On my module, R3 is 0R, R2 is 470 Ohms and R1 is 1500 Ohms. In the calculator above, R1 = 470 ohms and R2 =1500 ohms works out to 5.239V for an LM317. It works out to be 5.072V for the LT1963, which uses 1.21V instead of 1.25V in the formula. Note that R1 and R2 are reversed in the schematic in the datasheet. It should be as in the schematic in the calculator page.

I found a seller on AliExpress that makes them between 1.2vdc and 20vdc. Maybe an easy way to get an 4.7v