8
FN6409.0
December 18, 2006
and audio playback are intended to be mutually exclusive
operations.
Audio Switches
The two audio switches (L, R) are 3 switches that can pass
signals that swing below ground by as much as 1.5V. They
were designed to pass ground reference stereo signals with
minimal insertion loss and very low distortion. Crosstalk
between the audio switches over the audio band is < -110dB.
Over a signal range of ±1V (0.707Vrms) with V
DD
>2.7V,
these switches have an extremely low r
ON
resistance
variation. They can pass ground referenced audio signals
with very low distortion (<0.06% THD+N) when delivering
15.6mW into a 32
headphone speaker load. See Figures 8,
Figures 9, Figures 10, and Figures 11 THD+N performance
curves.
These switches are uni-directional switches. The audio
drivers should be connected at the L and R side of the switch
(pin 7 and pin 8) and the speaker loads should be connected
at the COM side of the switch (pin 3 and pin 4).
The audio switches are active (turned ON) whenever the IN
voltage is
0.5V and the CTRL voltage to 1.4V.
Note: Whenever the audio switches are ON the USB
transceivers need to be in the high impedance state or static
high or low state.
USB Switches
The two USB switches (D+, D-) are 5 bidirectional switches
that were designed to pass high-speed USB differential
signals in the range of ±0V to 400mV. These switches have
low capacitance and high bandwidth to pass USB
high-speed signals (480Mbps) with minimum edge and
phase distortion to meet USB 2.0 high-speed signal quality
specifications. See Figure 12 for High-speed Eye Pattern
taken with switch in the signal path.
The maximum signal range for the USB switches is from
-1.5V to V
DD
. The signal voltage at D- and D+ should not be
allow to exceed the V
DD
voltage rail or go below ground by
more than -1.5V.
The USB switches are active (turned ON) whenever the IN
voltage is
1.4V.
Note: Whenever the USB switches are ON the audio drivers
of the CODEC need to be at AC or DC ground or floating to
keep from interfering with the data transmission.
ISL54206 Operation
The discussion that follows will discuss using the ISL54206 in
the typical application shown in the block diagrams on page 7.
VDD SUPPLY
The DC power supply connected at VDD (pin 1) provides the
required bias voltage for proper switch operation. The part
can operate with a supply voltage in the range of 1.8V to
5.5V.
In a typical USB/Audio application for portable battery
powered devices the V
DD
voltage will come from a battery or
an LDO and be in the range of 2.7V to 3.6V. For best
possible USB full-speed operation (12Mbps) it is
recommended that the V
DD
voltage be 3.3V in order to get
a USB data signal level above 2.5V.
LOGIC CONTROL
The state of the ISL54206 device is determined by the
voltage at the IN pin (pin 2) and the CTRL pin (pin 10). Refer
to truth-table on page 2 of data sheet. These logic pins are
1.8V logic compatible when V
DD
is in the range of 2.7V to
3.6V and can be controlled by a standard
processor.
The CTRL pin is internally pulled low through a 4Mresistor to
ground and can be left floating or tri-stated by the µprocessor.
The CTRL control pin is only active when IN is logic “0”.
The IN pin does not have an internal pull-down resistor and
must not be allowed to float. It must be driven High or Low.
The voltage at the IN pin can exceed the V
DD
voltage by as
much as 2.55V. This allows the VBUS voltage from a
computer or USB hub (4.4V to 5.25V) to drive the IN pin
while the VDD voltage is in the range of 2.7V to 3.6V. An
external pull-down resistor is required from the IN pin to
ground when directly driving the IN pin with the computer
VBUS voltage. See the section titled “USING THE
COMPUTER VBUS VOLTAGE TO DRIVE THE “IN’ PIN”.
Logic control voltage levels:
IN = Logic “0” (Low) when IN
0.5V
IN = Logic “1” (High) when IN
1.4V
CTRL = Logic “0” (Low) when
0.5V or floating.
CTRL = Logic “1” (High) when
1.4V
Audio Mode
If the IN pin = Logic “0” and CTRL pin = Logic “1,” the part
will be in the Audio mode. In Audio mode the L (left) and R
(right) 3 audio switches are ON and the D- and D+ 5 USB
switches are OFF (high impedance).
When nothing is plugged into the common connector or a
headphone is plugged into the common connector, the
processor will sense that there is no voltage at the VBUS
pin of the connector and will drive and hold the IN control pin
of the ISL54206 low. As long as the CTRL = Logic “1,” the
ISL54206 part will be in the audio mode and the audio
drivers of the media player can drive the headphones and
play music.
USB Mode
If the IN pin = Logic “1” and CTRL pin = Logic “0” or Logic “1”
the part will go into USB mode. In USB mode, the D- and D+
5 switches are ON and the L and R 3 audio switches are
OFF (high impedance).
ISL54206
