The TPSI3100-Q1 includes two high-speed comparators on the secondary side. The information from both comparators is transmitted to the primary side; however, the fault comparator, when tripped, de-asserts the drive pin. At a system-level perspective, these signals can be sent to a microcontroller to provide current, voltage, or temperature monitoring. Although the fault comparator does not need a monitor to disable the driver, the information can still be useful. In this design, these comparators are used in an overcurrent protection circuit. This circuit is comprised of the unidirectional current sense amplifier INA180-Q1 which outputs into a resistor divider that feeds the fault and alarm comparators of the TPSI3100-Q1. The fault current is 25A because at a full 1000V charge the initial current can reach 20A. To reduce the risk of false positives throughout the life of the design, add some margin.

There are several different ways an ALM1_CMP comparator can be configured. Since this comparator cannot disable the driver, there is more flexibility in the precise meaning of the signal. Table 2-2 shows three examples of the ALM configuration.

In configuration 1, the alarm signal is not tripped on a regular basis as the circumstance requires a 1000V charge. Therefore, the alarm signal serves as a warning that the current has reached a level that can prove harmful to the components in the power path if not addressed quickly. Since the driver is disabled at 25A, the range of currents expected is between 20A and 25A. A reasonable time period for the alarm to be active under this operation is from 10ms to 50ms. The alarm information is transmitted across the isolation barrier in 30μs, which gives a microcontroller the ability to act if the alarm signal remains active.

In configurations 2 and 3, expect for the alarm signal to trip and remain tripped for a longer time. Similar to configuration 1, a microcontroller can be tasked with timekeeping and given authority to disable the device if the time limit is exceeded. Configuration 2 gives some more breathing room for the alarm signal to deactivate and configuration 3 is the temporal halfway point of the typical precharge cycle.

Beyond current and voltage sensing, the alarm and fault signals can be used for much more such as temperature or humidity. Because of the low latency with which the signals are transmitted to the primary side, more complex operations are possible with a microcontroller.