12 pF

SEND

/END

MIC

-

+

-

+

PULSE

GENERATOR

LDO

(2.3V/2/6V)

MR_COMP

SEND/END

LP8727

www.ti.com

SNVS898A – OCTOBER 2012 – REVISED MAY 2013

SEND/END BUTTON AND MICROPHONE REMOVAL DETECTION

The LP8727 supports SEND/END button and microphone removal detection features by monitoring voltage on ID

pin. When the microphone is connected to ID pin, it is biased by RES output through an external 2.2 k

Ω resistor.

In the event of removal of the microphone, the voltage on ID pin will go as high as the bias voltage which is

typically 2.3V, and this event will be detected by a comparator. The threshold for microphone removal detection

will be set to 90% of the bias voltage.

Headset accessories have a push button switch (SEND/END) between the ID pin and GND. In case that

SEND/END button is pressed, the voltage on ID pin will drop down to GND potential, and an internal comparator

is used to detect this event. The typical threshold of SEND/END button detection is set to 10% of the bias

voltage.

Both cases will generate interrupts to the host processor.

MICROPHONE LOW-POWER MODE

When the microphone is connected, it is powered from RES output through an external 2.2 k

Ω (typ.) resistor. In

case that the microphone is connected but not active, the LP8727 allows reducing the power dissipation at the

microphone, while it is still supporting SEND/END button and microphone removal detection.

During the microphone low-power mode, the internal 200 k

Ω resistor will be turned on for immediate microphone

removal detection, and RES output will cycling ON and OFF with a short period of time for SEND/END detection.

The microphone low-power mode is enabled by MIC_LP bit, and interrupts will be generated by SEND/END and

MR_COMP events.

Figure 3. MIC Low-Power Operation

EXPDET LDO

The EXPDET is overvoltage protected LDO output for low-voltage USB transceiver on the processor, or it can be

used as a startup trigger signal for the PMU.

The EXPDET LDO is directly powered from VBUS and can withstand up to 28V. The typical output voltage is set

to 4.85V and it is designed to supply up to 50 mA. For stable operation, a 1

μF ceramic capacitor is required at

the output.

Copyright © 2012–2013, Texas Instruments Incorporated

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Product Folder Links: LP8727