Datasheet

LM49370

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SNAS356D –FEBRUARY 2007–REVISED MARCH 2012

Table 18. MIC_2 (0x0Ch) (continued)

Bits Field Description

2:1 MIC_ This selects the voltage as a reference to the internal and external microphones. Only one bias pin is driven

BIAS_ at once depending on the INT_EXT bit setting found in the MIC_1 (0x0Bh) register. MIC_BIAS_VOLTAGE

VOLTAGE should be set to '11' only if A_V

> 3.4V. In OCL mode, MIC_BIAS_VOLTAGE = '00' (EXT_BIAS = 2.0V)

should not be used to generate the EXT_BIAS supply for a cellular headset external microphone. Please refer

to Table 19 for more detail.

MIC_BIAS_VOLTAGE EXT_BIAS/INT_BIAS

2.0V

2.5V

2.8V

3.3V

3 BUTTON_TYPE If set, the LM49370 assumes that the button (if used) in the headset is in series (series push button) with the

microphone, opening the circuit when pressed. The default is for the button to be in parallel (parallel push

button), shorting out the microphone when pressed.

5:4 BUTTON_ This sets the time used for debouncing the pushing of the button on a headset with a parallel push button.

DEBOUNCE_

BUTTON_DEBOUNCE_TIME Time (ms)

TIME

In OCL mode there is a trade-off between the external microphone supply voltage (EXT_MIC_BIAS -

OCL_VCM_ VOLTAGE) and the maximum output power possible from the headphones. A lower

OCL_VCM_VOLTAGE gives a higher microphone supply voltage but a lower maximum output power from the

headphone amplifiers due to the lower OCL_VCM_VOLTAGE - A_V

Table 19. External MIC Supply Voltages in OCL Mode

Available Recommended Supply to Microphone

A_V

EXT_MIC_BIAS

OCL_VCM_VOLT = 1.5V OCL_VCM_VOLT = 1.2V

> 3.4V 3.3V 1.8V 2.1V

2.9V to 3.4V 2.8V 1.3V 1.6V

2.8V to 2.9V 2.5V 1.0V 1.3V

2.7V to 2.8V 2.5V - 1.3V

Product Folder Links: LM49370