LM48822TL datasheet(14/22 Pages) NSC

14 / 22 page

SHUTDOWN FUNCTION

The LM48822 features three shutdown controls. Bits B6

(SDL) and B1 (SDR) of the MODE CONTROL register control

the left and right channels, respectively. Set the control bits

to 1 to disable the corresponding channel. When SDR = 1 and

SDL = 0, the right channel is disabled, the right and left inputs

are summed and output as a mono signal on the OUTL. When

SDL = 1 and SDR = 0, the left channel is disabled, while only

the right input signal is output on OUTR. Setting both SDL and

SDR = 1 disables both channels, while the charge pump re-

mains active. Bit B7 (SHDN) of the VOLUME CONTROL

Set SHDN = 1 to disable the entire device; both amplifiers and

charge pump are disabled. Set SHDN = 0 for normal opera-

tion. SHDN = 1 overrides any other shutdown control bit.

MUTE FUNCTION

Set bits B2 (MUTE_LEFT) and B0 (MUTE_RIGHT) of the

MODE CONTROL register to 1 to mute the respective chan-

nels. Set MUTE_LEFT and MUTE_RIGHT to 0 for normal

operation.

SD_BIAS FUNCTION

The LM48822 BIAS is controlled through the I2C interface. Set

bit B5 (SD_BIAS) of the MODE CONTROL register to 1 to

enable the LM48822 BIAS. BIAS provides the voltage for both

the amplifiers and the charge pump. When enabled, V

BIAS will

track V

DD for VDD < 3V. Once VDD exceeds 3V, VBIAS remains

fixed at 3V, limiting the output swing of the device the 6V

P-P.

Set SD_BIAS = 0 to disable BIAS. Disabling BIAS allows the

amplifier and charge pump to track V

DD, increasing output

swing; however, a slight degradation in PSSR will occur. Limit

DD to 4.2V or less when BIAS is disabled.

PROPER SELECTION OF EXTERNAL COMPONENTS

Power Supply Bypassing/Filtering

Proper power supply bypassing is critical for low noise per-

formance and high PSRR. Place the supply bypass capaci-

tors as close to the supply pins as possible. Place a 1

μF

ceramic capacitors from V

DD to GND. Additional bulk capac-

itance may be added as required.

Charge Pump Capacitor Selection

Use low ESR ceramic capacitors (less than 100m

Ω) for opti-

mum performance.

Charge Pump Flying Capacitor (C1)

The flying capacitor (C1) affects the load regulation and out-

put impedance of the charge pump. A C1 value that is too low

results in a loss of current drive, leading to a loss of amplifier

headroom. A higher valued C1 improves load regulation and

lowers charge pump output impedance to an extent. Above

2.2

μF, the R

DS(ON) of the charge pump switches and the ESR

of C1 and C2 dominate the output impedance. A lower value

capacitor can be used in systems with low maximum output

power requirements.

Charge Pump Flying Capacitor (C2)

The value and ESR of the hold capacitor (C2) directly affects

the ripple on CPV

SS. Increasing the value of C2 reduces out-

put ripple. Decreasing the ESR of C2 reduces both output

ripple and charge pump output impedance. A lower value ca-

pacitor can be used in systems with low maximum output

power requirements.

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 LM48822. The input capacitors create a high-

pass filter with the input resistors R

IN. The -3dB point of the

high pass filter is found using Equation (1) below.

f = 1 / 2

πR

INCIN

(Hz)

(1)

Where the value of R

IN is given in the Electrical Characteris-

tics Table.

High pass filtering the audio signal helps protect the speakers.

When the LM48822 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 fre-

quencies, 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 recommend-

ed for impedance matching and improved CMRR and PSRR.

SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION

The LM48822 is compatible with single-ended sources. Fig-

ure 7 shows the typical single-ended applications circuit.

30061056

FIGURE 7. Single-Ended Input Configuration

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