8 Controlled Gate-Sequencing Circuit

There is importance to control the PA during start-up, shutdown, and alarm conditions, to make sure that the PA is not damaged during these events. This is accomplished by creating a three input logic AND gate of key signals: V_REF, HOST PA_EN, and ALARM.

V_REF is used as the device good signal for the PA_ON output. This makes sure that the PA never has the drain voltage applied at start-up, as the V_REF must be enabled by the host controller after the AFE11612-SEP starts up. The ALARM signal from the AFE11612-SEP circuit can force the PA_ON to 0 V if the AFE11612-SEP detects any alarms. Finally, the host micro controller has the option of turning off PA_ON. Table 8-1 shows how all of the digital outputs interact with the PA_ON.

Here is an example of the PA_ON power on sequence:

1. The AFE11612-SEP is initialized. The host sends the command to turn on the V_REF. With no alarm state at startup, the ALARM pin is High-Z. The host keeps PA_EN Low to keep the PA off.
2. Next, the drain power is turned on. The host sets PA_EN High, enabling the PA_ON signal.
3. Third, an alarm condition is shown. The ALARM goes to 0V, turning off the PA_ON and thus turning off the PA to protect the PA.
4. Fourth, the alarm condition is cleared. ALARM returns to High-Z, and the PA_ON is on.
5. Lastly, before the part powers off, disable PA_EN to turn off the PA_ON. Power down the AFE11612-SEP.