-120

-100

-80

-60

-40

-20

0

10

100

1000

10000

100000

FREQUENCY (Hz)

LM48310

SNAS430D – NOVEMBER 2007 – REVISED MAY 2013

www.ti.com

Figure 30. Crosstalk vs Frequency

DIFFERENTIAL AMPLIFIER EXPLANATION

As logic supplies continue to shrink, system designers are increasingly turning to differential analog signal

handling to preserve signal to noise ratios with restricted voltage signs. The LM48310 features a fully differential

speaker amplifier. A differential amplifier amplifies the difference between the two input signals. Traditional audio

power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction of SNR relative to

differential inputs. The LM48310 also offers the possibility of DC input coupling which eliminates the input

coupling capacitors. A major benefit of the fully differential amplifier is the improved common mode rejection ratio

(CMRR) over single ended input amplifiers. The increased CMRR of the differential amplifier reduces sensitivity

to ground offset related noise injection, especially important in noisy systems.

POWER DISSIPATION AND EFFICIENCY

The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the

LM48310 is attributed to the region of operation of the transistors in the output stage. The Class D output stage

acts as current steering switches, consuming negligible amounts of power compared to their Class AB

counterparts. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET on-

resistance, along with switching losses due to gate charge.

SHUTDOWN FUNCTION

The LM48310 features a low current shutdown mode. Set SD = GND to disable the amplifier and reduce supply

current to 0.01µA.

Switch SD between GND and VDD for minimum current consumption is shutdown. The LM48310 may be disabled

with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.1µA value.

The LM48310 shutdown input has and internal pulldown resistor. The purpose of this resistor is to eliminate any

unwanted state changes when SD is floating. To minimize shutdown current, SD should be driven to GND or left

floating. If SD is not driven to GND or floating, an increase in shutdown supply current will be noticed.

AUDIO AMPLIFIER POWER SUPPLY BYPASSING/FILTERING

Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass

capacitors as close to the device as possible. Typical applications employ a voltage regulator with 10µF and

0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing

of the LM48310 supply pins. A 1µF capacitor is recommended.

12

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