In today’s automotive electronics, engineers are incorporating more functions inspired by personal electronics. As a result, audio jacks are starting to appear in cars nowadays. They could be used for rear-seat entertainment, detachable navigation units or automotive-grade tablets. Oftentimes, passengers like to use their own headsets when viewing individualized content. Not only does it maintain their privacy, but it also frees the driver from distractions as the passenger is viewing the content.
The audio jack used for these wired headphones is a standard 3.5mm connector. In the past, these audio jacks have been three-conductor jacks with a tip, ring and sleeve pin. As the industry moves forward, more advanced audio entertainment systems are implementing key press and voice command features that require a microphone input. The system then needs to support four-conductor jacks with a tip, two rings and sleeve pin. However, supporting a microphone presents a different issue for system designers because there are two types of four-pole jacks on the market with different microphone and ground locations.
With current market solutions, designers are typically required to hardwire the ground to one of the pins of the connector, rendering the other headset configuration unsupported. This leaves potential end-users of the system with incompatible headsets and an unpleasant realization that they can’t listen to their own audio.
Another desired feature for in-car headsets is a keypad with buttons, which would be compatible with all headsets. These would have common options like volume up, volume down and a mute key. A typical headset will have a resistor network associated with the keys. When the user presses a key, it creates a voltage divider network between the MICBIAS output of the codec and the system ground. This will be a measurable voltage on the SLEEVE/RING2 pin. A system designer looking to support these keys currently has two options: Find a codec with the appropriate detection means and key press “buckets” or use an appropriate external ADC with all of the associated hand calculations for the resistor divider and voltage network.
High-performance audio jack switches, like the TS3A225E, help solve these issues by automatically detecting any configuration of audio headset and routing the ground and microphone lines to the appropriate pin. By looking at the resistor network created by the headset’s speakers and mic (or lack of mic), the switch series is able to determine where the ground line and microphone are located. Once the location has been determined, the microphone connection from the codec is automatically routed to the appropriate pin, allowing the system to support every headset on the market. TI’s latest audio jack switch, the TS3A227E, integrates the key press detection, easing system design by automatically detecting the standard industry keys and reporting this information back to the host.
By incorporating audio jack switches, automotive system designers can be ready to meet the latest challenges and enhance the overall experience of tomorrow’s end user.