LM49150, LM49150TLEVAL

SNAS439C – AUGUST 2008 – REVISED MAY 2013

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Table 8. Volume Control Table (continued)

Volume Step

xG4(1)

xG3

xG2

xG1

xG0

Gain (dB)(2)

30

1

1

1

0

1

15.00

31

1

1

1

1

0

16.50

32

1

1

1

1

1

18.00

SHUTDOWN FUNCTION

The LM49150 features the following shutdown controls.

Bit B4 (GAMP_SD) of the SHUTDOWN CONTROL register controls the gain amplifiers. When GAMP_SD = 1, it

disables the gain amplifiers that are not in use. For example, in Modes 1, 4 and 5, the Mono inputs are in use, so

the Left and Right input gain amplifiers are disabled, causing the IDD to be minimized.

Bit B0 (PWR_On) of the SHUTDOWN CONTROL register is the global shutdown control for the entire device.

Set PWR_On = 0 for normal operation. PWR_On = 1 overrides any other shutdown control bit.

OUTPUT MODE CONTROL

In the LM49150 OUTPUT MODE CONTROL register (Table 4), Bit B5 (EP Bypass) controls the operation of the

Earpiece Bypass path. If EP Bypass = 0, it would act under normal output mode operation set by bits B3, B2, B1,

and B0. If EP Bypass = 1, it overrides the B3, B2, B1, and B0 Bits and enables the Receiver Bypass path, a

class AB amplifier, to the speaker output.

Bit B4 (HPR_SD) of the OUPUT MODE CONTROL register controls the right headphone shutdown. If HPR_SD

= 1, the right headphone output is disabled.

DIFFERENTIAL AMPLIFIER EXPLANATION

The LM49150 features a differential input stage, which offers improved noise rejection compared to a single-

ended input amplifier. Because a differential input amplifier amplifies the difference between the two input

signals, any component common to both signals is cancelled. An additional benefit of the differential input

structure is the possible elimination of the DC input blocking capacitors. Since the DC component is common to

both inputs, and thus cancelled by the amplifier, the LM49150 can be used without input coupling capacitors

when configured with a differential input signal.

SINGLE-ENDED INPUT CONFIGURATION

The left and right stereo inputs of the LM49150 are configured for single-ended sources (see Figure 1).

INPUT CAPACITOR SELECTION

Input capacitors may be required for some applications, or when the audio source is single-ended. Input

capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of

the audio source and the bias voltage of the LM49150. The input capacitors create a high-pass filter with the

input resistors RIN. The -3dB point of the high-pass filter is found using Equation 1 below.

f = 1 / 2

πRINCIN (Hz)

Where

•

value of RIN is given in the Electrical Characteristics Table.

(1)

High-pass filtering the audio signal helps protect the speakers. When the LM49150 is using a single-ended

source, power supply noise on the ground is seen as an input signal. Setting the high-pass filter point above the

power supply noise frequencies, 217Hz in a GSM phone, for example, filters out the noise such that it is not

amplified and heard on the output. Capacitors with a tolerance of 10% or better are recommended for impedance

matching and improved CMRR and PSRR.

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