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3.5 mm Headset Jack: Device Specification

In this document

To achieve compatibility with the 3.5 mm plug headset specification, devices that include a 4 conductor 3.5 mm audio jack must meet the following specifications. For Android compatibility requirements, refer to the Analog audio ports section of the Android CDD.


Function Device Support
Stereo Audio Out Required
Audio in (Mic) Required
Ground Required

Software mapping

Function Device Support Description
Function A control event Required Input event: KEY_MEDIA


Function D control event Required Input event: KEY_VOICECOMMAND


Function B control event Required Input event: KEY_VOLUMEUP

Android key: VOLUME_UP

Function C control event Required Input event: KEY_VOLUMEDOWN

Android key: VOLUME_DOWN

Headset insertion detection Required Input event: SW_JACK_PHYSICAL_INSERT 7
Headset type detection Mic Input event: SW_MICROPHONE_INSERT 4
No Mic Input event: SW_HEADPHONE_INSERT 2
Headset speaker impedance Required Headphone (low) Failure mode is to indicate headphones so limitation would be on
Required Line In (high) Input event: SW_LINEOUT_INSERT 6


Function Device Support Description
4 conductor 3.5 mm jack Required
CTIA pinout order (LRGM) Required 3 Pin & Mono Plug Compatible
OMTP pinout order (LRMG) Optional but strongly recommended
Headset detect sequence Required Plug insert notification must be triggered only after all contacts on plug are touching their relevant segments (this prevents unreliable headset detection due to slow insertion.



Function Device Support Notes
Maximum output voltage drive 150mV >= 150mV on 32 ohm

Test conditions: EN50332-2

Mic bias resistance Required Flexible on detection method used and microphone bias resistor selection. Require that all button resistance value ranges specified below be detected and related to their respective function
Mic bias voltage 1.8V - 2.9V To guarantee compatibility to common microphone capsules.

Function impedance and threshold detection

Devices must detect the following resistor ladder on the accessories. The accessories will be tested to the standardized circuit diagram in the diagram illustrated earlier (Reference Headset Test Circuit) where the total impedance is measured from MIC terminal to GND when a button is pressed with 2.2V mic bias applied through 2.2 kOhm resistor. This is the same effective resistance as the button detection circuit with the microphone in parallel with the button resistor.

Button Impedance Level Device Support Notes
70 ohm or less Required [Function A]
110 - 180 ohm Required [Function D]
210 - 290 ohm Required [Function B]
360 - 680 ohm Required [Function C]
Headset Speaker Impedance Level Device Support Notes
Low Threshold Detection Required Headphone (low) < 1 Kohm
High Threshold Detection Required Line In (high) > 5 Kohm
4-Segment Plug Detection Resistance (between 3rd and 4th segment) Device Support Notes
4-Segment Plug Threshold Required Resistance >= 100 ohms
3-Segment Plug Threshold Required Resistance < 100 ohms