4 ESD Robustness

To address ESD robustness, certain logic was moved from one location in the chip to another. This change was not done on any modules that are critical for metrology. Additionally, ESD tests with respect to e-meters are system-level tests. Therefore, bolstering the chip's ESD performance may not compensate for any ESD issues that arise due to design weaknesses.

TI recommends following ESD guidelines and performing proper ESD testing when creating a new design or when migrating between devices. Recommendations include following PCB layout recommendations, using ESD protection devices, enabling NMI interrupts to detect or prevent unexpected resets, and enabling the oscillator fault interrupt to detect oscillator disturbances. For more guidelines and recommendations on how to create robust system-level designs, see MSP430 System-Level ESD Considerations.

To test the comparative ESD robustness of the MSP430F67xxA, an IEC 61000-4-2 test was performed on one EVM430-F6779 (see Figure 1 for EVM picture) that had the MSP430F67791A as the metering SoC and another EVM430-F6779 that had the non-A MSP430F67791 as the metering SoC. For the EVM430-F6779, some ESD tradeoffs were made to support fully showcasing the features of the silicon and ease of use for evaluation purposes. However, the EVM can still be used as a gauge to show the improvements of the MSP430F67xxA devices.

Figure 1. EVM430-F6779

For applying the ESD test on the two test EVMs, both positive and negative polarity discharges were applied on both test boards at the same location. In the tests, recoverable failures (for example, a reset), lock-ups, and latch-ups were logged as failures. Because the only items that differed between the two tested boards was whether a MSP430F67791A or MSP430F67791 was installed, this test shows the additional robustness due to upgrading to the A version of the MSP430F67xx chips. Table 1 shows the results of these tests:

As shown in the table, by upgrading the MSP430F67791 chips in the EVM430-F6779 with the MSP430F67791A, the ESD robustness improved at the test point by at least 8-10 kV. In addition, the F67791A results would pass even level 4 of IEC 61000-4-2. For more details on these MSP430F67791(A) ESD tests, refer to the TI Design Three-Phase Metrology with Enhanced ESD Protection and Tamper Detection (TIDM-3PHMTR-TAMP-ESD).

In addition to performing ESD tests on the EVM430-F6779, a similar test was performed with one EVM430-F6736 (see Figure 2 for an EVM picture) that had the MSP430F6736A and another one that had the MSP430F6736. For testing the EVM430-F6736, the ESD strike was applied at four locations: near the top, bottom, left, and right of the EVMs. Table 2 through Table 5 show the results of these tests.

Figure 2. EVM430-F6736

These tables show that replacing a MSP430F6736 with a MSP430F6736A could improve a design's ESD robustness. For more details on these MSP430F6736(A) ESD tests, refer to the TI Design One-Phase Metrology with Enhanced ESD Protection (TIDM-1PHMTR-ESD).