LM4666, LM4666SDBD

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SNAS189A – MAY 2004 – REVISED MAY 2013

The rising and falling edges are necessarily short in relation to the minimum pulse width (160ns), having

approximately 2ns rise and fall times, typical, depending on parasitic output capacitance. The inductive nature of

the transducer load can also result in overshoot on one or both edges, clamped by the parasitic diodes to GND

other components in the system and cause interference. It is essential to keep the power and output traces short

and well shielded if possible. Use of ground planes, beads, and micro-strip layout techniques are all useful in

preventing unwanted interference.

As the distance from the LM4666 and the speakers increase the amount of EMI radiation will increase since the

output wires or traces acting as antenna become more efficient with length. What is acceptable EMI is highly

application specific. Ferrite chip inductors placed close to the LM4666 may be needed to reduce EMI radiation.

The value of the ferrite chip is very application specific.

POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply

applications employ a voltage regulator with a 10µF and a 0.1µF bypass capacitors that increase supply stability.

These capacitors do not eliminate the need for bypassing on the supply pin of the LM4666. A 1µF tantalum

capacitor is recommended.

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the LM4666 contains shutdown circuitry that reduces

current draw to less than 0.01µA. The trigger point for shutdown is shown as a typical value in the Electrical

Characteristics Tables and in the Shutdown Hysteresis Voltage graphs found in the Typical Performance

Characteristics section. It is best to switch between ground and supply for minimum current usage while in the

shutdown state. While the LM4666 may be disabled with shutdown voltages in between ground and supply, the

idle current will be greater than the typical value. Increased THD may also be observed with voltages less than

The LM4666 has an internal resistor connected between GND and Shutdown pins. The purpose of this resistor is

to eliminate any unwanted state changes when the Shutdown pin is floating. The LM4666 will enter the shutdown

state when the Shutdown pin is left floating or if not floating, when the shutdown voltage has crossed the

threshold. To minimize the supply current while in the shutdown state, the Shutdown pin should be driven to

GND or left floating. If the Shutdown pin is not driven to GND, the amount of additional resistor current due to the

internal shutdown resistor can be found by Equation 1 below.

(1)

With only a 0.5V difference, an additional 8.3µA of current will be drawn while in the shutdown state.

GAIN SELECTION FUNCTION

The LM4666 has fixed selectable gain to minimize external components, increase flexibility and simplify design.

high level. For a differential gain of 12dB, the Gain Select pin should be permanently connected to GND or driven

to a logic low level. The gain of the LM4666 can be switched while the amplifier is in PLAY mode driving a load

with a signal without damage to the IC. The voltage on the Gain Select pin should be switched quickly between

typical threshold voltages for the Gain Select function, refer to the Gain Threshold Voltages graph in the Typical

Performance Characteristics section.

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