TIDA-01445: Desing requirement for alternating currents

Hi Michael,

TPS2H000-Q1 is used for PWM control and read back the PWM signals by the MCU which is called "Dynamic state".

VCC_INT is a fixed value then the current went through is almost fixed once the interlock resistance is small enough.

The reason to add both approaches is redundant for different application. As you know, only PWM method can not detect high interlock resistance, for example, not good connection or the wire.

Actually in you system, you can separate these two approach into two different channels. This will make your system more robust.

Hi Michael,

As we can see in the market that both methods are existing in designs. Here are some reasons from my perspective. You can correct me if it is not correct.

HVIL circuit is used to detect whether there is a high voltage/power cable broken in the system. In together with the high voltage cable, actually there is a low voltage cable to represent the high voltage cable status. Normally the low voltage cable looks like "short".

(1) PWM approach is easy to achieve, especially for the detection circuit. For example, typical using high-side switch to generate 100Hz PWM signal. And in the low-side, there is almost no need of protection as the resistor values can be large which directly to MCU to detect the PWM signals. This will make the circuit simple and cost low. However, this approach is not sufficient to detect special fault "pre-broken" which means that the cable is still there but the resistance becomes a little larger than the normal case. 

(2) Constant current approach can almost solve the PWM problem as there will be a constant current, typically 10mA~30mA. We only need to measure the voltage across a fixed resistor to judge whether there is a fault. For example, realize a constant current source in the high-side, and use a resistor in low side to measure it, just like our reference design. We need to add protection circuit for both high-side and low-side as the signals are two small. And the measure in low side is more complicated. This will make this solution more expensive compared with PWM approach.

(3) In combine, if functional safety like AISL-C/D is required for the HVIL, it's more common to use these redundant approaches together to avoid common mode failure,