MSP430F6779A: EFT according to IEC 61000-4-4 to TI design

Hello,

First, thank you for including the analog front end (AFE) portion of your schematic with your question.

In our Differences Between MSP430F67xx and MSP430F67xxA Devices app note, the ESD performance between the F67xx and F67xxA was compared. As you can see in Table 1, the test results for the F67xxA device are much better for the IEC 61000-4-2 tests. Can you confirm if you're using F67xx or F67xxA?

Another excellent reference is our TIDM-3PHMTR-TAMP-ESD TI Design and its design guide.

Next, I understand that you're performing IEC 61000-4-4 test instead of IEC 61000-4-2. Looking at our IEC 61000-4-x Tests for TI’s Protection Devices app note, the IEC 61000-4-2 test is related to system ESD immunity whereas the IEC 61000-4-4 test is related to Electrical Fast Transient Immunity (EFT). Section 2.3 discusses using transient voltage suppression (TVS) diodes to supress the EFT events. Figure 5 illustrates the expected bursts and waveforms.

Since our TI Designs have been targeted towards IEC 61000-4-2, they use varistors as the protection devices. These work fine for an ESD strike, but they tend to age or degrade over time when exposed to bursts over extended periods of time, which could be the reason why you're seeing the device stop. Thus, I would suggest adding TVS diodes to your system (assuming in parallel with your varistor, RV2, but double-check) to protect against EFT events. I'd recommend looking at the following resources as well.

• IEC ESD, EFT, and Surge RS-485 Bus Protection TI Design

• MSP430™ System-Level ESD Considerations

Regards,

James

MSP Customer Applications