2 Failure Analysis

Oscilloscope measurements captured significant overshoot and undershoot events during ICT operation. The worst-case overshoot measured 8.62V, while the worst-case undershoot measured -4.28V. These values exceeded the datasheet absolute maximum ratings of 6.5V and -0.5V, respectively for V_IO – I²C bus voltage range. The transient spikes therefore subjected the device pins to electrical overstress conditions. See figure 2-2 note (1) of this document for overshoot behavior. See Figure 2-3 of this document for undershoot behavior.

In addition to exceeding absolute maximum V_IO specifications, there exists a signal contention between the driver of the ICT and the TCA9617 B-side pedestal during a low-to-high edge transition on B-side. The pedestal behavior can be seen in the TCA9617 datasheet Figure 6-4, Figure 7-1, or Figure 8-2 point 2, and is described in Application Information.

When TCA9617 is driven from B-side to A-side, it expects an open-drain driver configuration. When the open-drain driver on B-side releases the bus, a pull-up resistor on B-side will pull-up to V_CCB. During this time, the buffer will reach a voltage pedestal (~V_OLB = 0.53V typical). The B-side will remain at this V_OLB until the A-side surpasses a 30% of V_CCA. Once this occurs, B-side is no longer held at V_OLB, and is allowed to rise fully to V_CCB through the pull-up resistor. If a push-pull driver is used during this edge transition from low-to-high on B-side, there will exist a contention between the pedestal voltage (V_OLB) and the push-pull driver, resulting in a large amount of current sink into the buffer - see Figure 2-2 of this document.