Safely connecting 4056 and MSP430

Started by kynix, November 01, 2016, 09:00:43 AM

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I'm using MSP430G2553IN20 microcontroller( on LaunchPad to drive an 4056 chip (HCF4056B to be precise) and a 7 segment display. The 4056 is set to sink current.

I've connected the port 2 pins, set as outputs, to the BCD and STROBE input pins of the 4056. The board with 4056 and display has its own separate power supply and the MSP430 is powered via the LaunchPad which provides it around 3.6 V. The grounds of both supplies are connected and I've set the other power supply as close as possible to 3.6 V.

I'm concerned that with this setup I could damage the chips. For example, when the 4056 power is down, it and the display are still getting some power from the MSP430 via the BCD and STROBE pins and the display remains on, although sometimes it works incorrectly.

Right now, I'm using 220 Ω220 Ω resistors on the output pins of the MSP430 to limit the output current, but I'm afraid that the setup isn't safe enough.

So my question is: Is there a simple and safe way to connect the MSP430 to the 4056? For best results, I'd want to drive 4056 at higher voltage than MSP430, but if that's too difficult I could settle for 3.6 V.