Figure 4-6 shows the STO_2 subsystem.

Figure 4-6 STO_2 subsystem (1oo1d)

The 24-V isolated digital input receiver ISO1211 converts the STO_2 input signal to a 3V3 CMOS level signal. The STO_1 signal from the output of the ISO1211 then pass through low pass RC filter to remove 1ms diagnostics pulses present on STO_2 signal. The output of ISO1211 (MCU_STO_2_In) is also monitored by the MCU (SIL 1) for stuck high faults. The low-pass filtered STO_2 signal is ANDed with MCU diagnostic signal (MCU_Diag_Cntrl_Out2) to generate load switch STO2_EN signal. The STO_2_EN signal is used to enable (logic high) and disable (logic low) the high-side load switch, which in turn control the input voltage P24V of the isolated gate supply TIDA-00199. The output of the TIDA-00199 provides 4 bipolar rails (+15 V, 8 V) to supply the six IGBT gate drivers ISO5852S (or ISO5452) VCC2 and VEE2. When the P24V input to TIDA-00199 is disconnected, the VCC2 and VEE2 supplies to the six gate drivers decay to 0V. All 6 isolated gate drivers ISO5852S (or ISO5452) will be disabled, which set the output of the ISO5852S (or ISO5452) gate driver to 0V or high-impedance. With the external pull-down resistors, the six IGBTs will turn off. The STO_2_FB signal used by the STO_FB logic to monitor the state of the drive.