10

FN6581.0

February 25, 2009

The minimum recommended supply voltage is 1.8V. It is

important to note that the input signal range, switching times,

and ON-resistance degrade at lower supply voltages. Refer

to the “Electrical Specifications” tables, beginning on page 3,

and “Typical Performance Curves”, beginning on page 11,

for details.

V+ and GND also power the internal logic and level shifters.

The level shifters convert the input logic levels to V+ and

GND signals levels to drive the analog switch gate terminals.

A high frequency decoupling capacitor placed as close to the

V+ and GND pin as possible is recommended for proper

operation of the switch. A value of 0.1µF is highly

recommended.

Negative Signal Capability

The ISL54062 contains circuitry that allows the analog input

signal to swing below ground. The device has an analog

signal range of 6.5V below V+ up to the V+ rail (see

example, if V+ = 5V, then the analog input signal range is

from -1.5V to +5V. If V+ = 2.7V then the range is from -3.8V

to +2.7V.

Click and Pop Operation

The ISL54062 contains circuitry that prevents audible click

and pop noises that may occur when audio sources are

powered on or off. Single supply audio sources are biased at

a DC offset that can generate transients during power on/off.

A DC blocking capacitor is needed to remove the DC bias at

the speaker load. For 32

Ω headphones, a 220µF capacitor is

typically used to preserve the audio bandwidth. The power

on/off transients are AC coupled by the 220µF capacitor to

the speaker load causing a click and pop noise.

The ISL54062 has shunt switches on the NO and NC pins to

eliminate click and pop transients (see Figure 10). These

switches are driven complimentary to the main switch. When

NC is connected to COM, the shunt switch is active on the

NO pin (and vice versa). The shunt switches connect an

impedance (140

Ω typical, see Figure 24) from the NO/NC

pin to ground to discharge any transients that may appear on

the NO or NC pins.

When a DC bias becomes active at the source, the NO and

NC terminals will also have a DC offset due to capacitor

dv/dt principle. The DC offset will be discharged through the

shunt impedance on the NO and NC terminals instead of the

speaker, eliminating click and pop noise.

*Under high impedance loads such as the input impedance

of pre-amplifiers (20k

Ω), the COM terminal voltage may rise

due to small leakage currents charging the COM

capacitance. This is not seen when low impedance loads

such as headphones (32

Ω) are used because the small

leakage currents does not result in significant potential drop

across the load. If the user desires to reduce the voltage

build up on the COM pin, a 1k

Ω resistor to ground may be

placed on the COM pin. This impedance is small enough to

reduce the voltage build up significantly while not increasing

the power dissipation dramatically. Current consumption

considerations will need to be taken for driving a smaller

load impedance under this scenario.

Click and Pop Elimination with INx Pin

Audio click and pop elimination can be driven with the Input

Select (INx) pin. When INx = 0, the NOx terminals are

connected to the shunt impedance. When INx = 1, the NCx

terminals are connected to the shunt impedance. In this

situation, only one of the source transient voltages will be

shunted to ground, depending on the Input Select state. The

Input Select pin should be driven 200ms after any source

transients occurs to prevent audible transients at the

speaker load.

Logic-Level Thresholds

is still below the 1.8V CMOS guaranteed low output

maximum level of 0.45V, but noise margin is reduced to

While this is above the 1.8V CMOS guaranteed high output

minimum of 1.35V, under most operating conditions the

switch will recognize this as a valid logic high.

The digital input stages draw supply current whenever the

digital input voltage is not at one of the supply rails. Driving

the digital input signals from GND to V+ with a fast transition

time minimizes power dissipation. The ISL54062 has been

designed to minimize the supply current whenever the digital

input voltage is not driven to the supply rails (0V to V+). For

example, driving the device with 2.85V logic high while

operating with a 4.2V supply the device draws only 1µA of

current.

IN

COM

220µF

32

Ω

NO

NC

V+

GND

C

AUDIO

SOURCE A

220µF

AUDIO

SOURCE B

ISL54062

FIGURE 10. CLICK AND POP OPERATION

ISL54062