8
FN6983.1
January 14, 2010
Detailed Description
The ISL54409, ISL54410 are +2.7 to +5.0V, Single Pole
Single Throw (SPST) audio switches that are negative
swing capable. The switch outputs (COM-, COM+) have
low OFF capacitance (4pF) that is capable of multiplexing
USB2.0 HS data and audio signals in a wired-OR
configuration for common connector applications (see
“Application Block Diagrams” on page 2). The ISL54409
features a low power shutdown mode while the ISL54410
features audio Click and Pop Elimination circuitry.
The ISL54409, ISL54410 are offered in a 8 Ld
2mmx2mm TDFN or 10 Ld 1.4x1.8mm
µTQFN packages.
Power Supply Considerations
The ISL54409, ISL54410 operates on a +2.7V to +5.0V
power supply. A 0.1
µF local decoupling capacitor placed
as closed as possible from the V
DD
pin to GND is highly
recommended for stable operation.
Audio Switches
The ISL54409, ISL54410 switches are designed to have
low THD+N from a signal range of -1V to +1V for audio
applications (see Figures 8 through 11). The
ON-resistance of the audio switches have a typical
resistance of 2.6Ω.
The analog signal range of the audio switches are
capable beyond -1V to +1V however, the ON-resistance
of the switches increases beyond it. The THD+N
performance deteriorates beyond a signal range of -1V to
+1V.
Audio/USB wired-OR Application
The ISL54409, ISL54410 allows the connection of an
audio codec and USB Controller to a common connector.
For audio mode of operation, the switch is closed to pass
low distortion audio from the codec to a headphone.
When the switch is open, USB2.0 HS data (480MBps) can
be transmitted to a host controller with minimal signal
degradation.
Since the USB device is always connected to the COM-
and COM+ pins on the ISL54409, ISL54410,
considerations must be taken to protect the USB
Controller when passing audio signals through the
switch. The USB2.0 specification requires the USB data
line to sustain a signal of -1V without damage to the
device. Audio signals from the codec may swing below
-1V in some applications. Since the USB Controller is
high impedance when not operating, exceeding -1V may
cause high leakage currents or damage sensitive devices
on the USB device. It is highly recommended to keep the
audio signal range within -1V to +1V.
USB V
BUS
Hot Plug Operation
The ISL54409, ISL54410 allows the hot plug operation of
the USB V
BUS
signal to operate the switch. This can be
accomplished by connecting CTRL to V
DD
at all times.
The V
BUS
signal from the USB Host is used to drive the
IN logic pin. Note from the “Absolute Maximum Ratings”
on page 5 that the IN pin must be kept below V
DD
.
Exceeding V
DD
by putting the 5V V
BUS
signal to the IN
pin will forward bias the ESD diode on the IN pin, which
will draw excessive diode current and result in a
damaged pin on the device. To prevent damage to the IN
pin, it is recommended to place a current limiting series
resistor or use a voltage divider to bring the voltage at
the IN pin below V
DD
. A 10kΩ series resistor will reduce
current significantly to prevent possible damage to the IN
pin. For further protection, a voltage divider with
R
T
=10kΩ will reduce the IN voltage below V
DD
with no
impact on logic threshold voltages (see Figure 5).
Low Power Shutdown/Click and Pop Mode
When the CTRL and IN pins are at logic “0”, the ISL54409
and ISL54410 enter into a disabled mode of operation. In
the disabled mode of operation, both switches are turned
OFF. For the ISL54409, the disabled mode is Low Power
Shutdown. The device is brought to a low powered state
and the I
cc
current is significantly reduced.
*Note: When placed in the Low Power Shutdown state,
the internal charge pumps that generate the negative
supply rails for negative signal swing capability are
turned off to reduce power consumption. With the
internal negative supply rail disabled the ISL54409 will
have poor isolation and crosstalk performance for
negative signal swings on the switch terminals. Negative
voltages will have a low impedance path to the other
switch terminals. It is not recommended to operate the
switch in Low Power Shutdown if the audio codec will
remain active when transmitting USB data on the COM-
and COM+ pins.
For the ISL54410, the disabled mode is Audio Click and
Pop Elimination. The switch input pins LIN and RIN have
their active Click and Pop circuitry enabled, which turns
on a typical 40Ω shunt resistance from the switch input
pin to GND. Some audio application requires DC biasing
the audio codec above ground for full output signal
swing. The audio signal must have the DC component
removed with a blocking capacitor at the headphone
load. This blocking capacitor is typically the source of
audible click and pop transients when the audio codec
powers up or down with the DC bias. The negative signal
swing capability of the audio switch allows the DC
blocking capacitor to be placed on input side of the
switch, which allows the Click and Pop Elimination
circuitry to discharge the DC blocking capacitor of any
transient currents, eliminating audio clicks and pops.
V
DD
GND
CTRL
0.1µF
COM-
COM+
LIN
RIN
IN
ISL54409
ISL54410
*R
T
*R
IN
V
BUS
= 5V
*R
IN
= 10k
Ω
*R
T
= Optional
FIGURE 5. USB V
BUS
HOT PLUG PROTECTION
ISL54409, ISL54410
