The TV-detection feature of the OPA361-Q1 works in conjunction with the OMAP242x (or other processors) to detect if a television is connected to the video output of the device. In order to detect a TV load, the OPA361-Q1 is briefly turned off, ideally during the first vertical sync pulse. For the detection, a simple pull-up resistor to the processor logic supply is used on the output of the OPA361-Q1. The voltage level is pulled LOW if the TV (or other video equipment) is connected, or HIGH if nothing is connected. A GPIO in the processor can be used to read this logic level and decide if a video load is connected. Figure 5-8 shows a scope plot with the TV disconnected and Figure 5-9 shows a scope plot with the TV connected; the upper line in both figures is the disable pulse. Figure 5-10 shows a circuit drawing using the TV-detect signal to disable or enable the OPA361-Q1.

Figure 5-8 Output of OPA361-Q1 Pulled Up To 1.8V During Disable: TV Disconnected

Figure 5-9 Output of OPA361-Q1 Pulled Down: TV Connected.

Figure 5-10 Using TV-Detect Signal to Disable/Enable the OPA361-Q1

Disabling the OPA361-Q1 also disconnects the internal feedback resistors’ path to GND, and therefore there is no current flowing from the logic supply through the pull-up resistor to GND if no video load is connected; this helps to conserve battery life. The typical leakage when the output is pulled high and OPA361-Q1 is disabled is only about 300pA.

The following functionality can be achieved by implementing TV-detection:

• Automatic video start by polling the video line periodically.
• Automatic video stop if the TV (or other equipment) is disconnected.

Proper implementation allows to significantly simplify the user interface.

For more information, see Application Report SBOA109, OPA361-Q1 and TV Detection, available for download at www.ti.com.