I tend to ramble, so let me ask my question simply, and then provide background after. If the SN74HC373 is powered by 5.0V, will a 3.3 V source from an be MCU reliably considered HIGH level.
The background is this.
I'm working with a module that uses a TI mcu (CC2511F32) powered from a 3.3 volt regulated source, in a larger circuit that also has regulated 5.0VDC for the main power. I'm using several of the MCU I/O pins configured as inputs, to sense button presses (8 buttons present). All these inputs are internally pulled up to 3.3V, and one side of all the buttons is tied to 0V. So now I'd like to add a little LED next to each button that lights when a button is pressed, and then stays lit. To do this with minimum parts, I'd like to employ a TI SN74HC373 as follows. All the "D" inputs of the chip will be tied to the button inputs. The, all the Q outputs will connect to low current LEDs through a resistor, tied to 5V VCC. Finally, I'll use another spare I/O line on the MCU to send a pulse to the LE pin on the IC, whenever I sense a new button hit. The desired result should be that regardless of what button (or combination of buttons) are pressed, the corresponding LEDs light and remain on.
But here's the issue . I'd like to power the 74HC373 with the 5V supply if I can, because the 3.3V regulator would be unacceptably taxed if I used it for this add on. So to do this without additional parts, the 3.3V present on all the pulled up MCU inputs, as well as 3.3V pulse I provide for the LE, will have to reliably be considered "HIGH" by the IC. Unfortunately its unclear from the data sheet whether or not this will work. The data sheet provides "Minimum High Level Input Voltage" of 1.5, 3.15, and 4.2 volts, for VCCs of 2, 4.5, and 6 volts, respectively. Since 5VDC is such a common voltage, I'm a bit surprised it wasn't included. At 4.5 V. it looks like 3.15 will work, but what about at 5V? Will my 3.3V be sufficient? Maybe I should add a diode in the VCC to the IC to drop it down to 4.5V?
I realize I'm cutting things close here, but again I want to accomplish the goal with as few parts as possible.