ISL54400 Datasheet, PDF (10/15 Pages) Intersil Corporation – Low Voltage, Dual SPDT, USB/Audio Switches with Negative Signal Capability

ISL54400, ISL54401, ISL54402
Application Block Diagram
V_BUS
D-/L
V_DD
ISL54400
V_TERM
D-
D+
D+/R
L
R
USB
FULL-SPEED
TRANSCEIVER
CODEC
GND
Detailed Description
The ISL5440X family of devices are dual single pole/double
throw (SPDT) analog switches that operate from a single
power supply. They were designed to function as dual 2 to 1
multiplexers to select between USB differential data signals
and audio L and R stereo signals. They come in tiny µTQFN
and TDFN packages for use in MP3 players, PDAs,
cellphones, and other personal media players.
All devices in this family consist of two 1Ω normally closed
(NC) audio switches and two 5Ω normally open (NO) USB
switches. The audio switches can accept signals that swing
below ground. They were designed to pass audio left and
right stereo signals, that are ground referenced, with minimal
distortion. The USB switches were designed to pass
full-speed USB differential data signals with minimal edge
and phase distortion.
The ISL54400 and ISL54401 were specifically designed for
MP3 players, personal media players and cellphone
applications that need to combine the audio headphone jack
and the USB data connector into a single shared connector,
thereby saving space and component cost. A typical
application block diagram of this functionality is shown
above. The ISL54400 and ISL54401 incorporate circuitry for
the detection of the USB V_BUS voltage, which is used to
switch between the audio CODEC drivers and USB
transceiver of the MP3 player or cellphone. The ISL54400
contains additional circuitry to generate the required USB
V_TERM of 3.3V for use with the USB speed setting pull-up
resistor.
The ISL54402 is an audio/data switch and its functionality is
typical of a standard dual SPDT device.
A detailed description of the two types of switches and of
each part type in the ISL5440x family are provided in the
sections below. The USB transmission and audio playback
are intended to be mutually exclusive operations.
10
Audio Switches
The two NC (normally closed) audio switches (L, R, NCx)
are 1Ω switches that can pass signals that swing below
ground. Crosstalk between the audio switches is < -110dB
and has a -3dB bandwidth of 394MHz.
The recommended maximum signal range is from -1.5V to
1.5V. You can apply positive signals greater than 1.5V but
the R_ON resistance of the switch increases rapidly above
1.5V. The audio signal should not be allowed to exceed the
V_DD rail or swing more negative than -1.5V.
Over a signal range of ±1V these switches have an
extremely low R_ON flatness. They can pass ground
referenced audio signals with very low distortion (<0.01%
THD+N) when delivering 12mW into a 32Ω headphone
speaker load. See Figures 8 and 9 THD+N performance
curves.
These switches are uni-directional switches. The audio
sources should be connected at the NC side of the switch
(pins 7 and 8) and the speaker loads should be connected at
the COM side of the switch (pins 3 and 4).
For the ISL54400 and ISL54401 parts the audio switches are
active (turned ON) whenever the V_BUS voltage is ≤ to V_DD +
0.2V. The V_BUS pin is internally pulled low through a
pulldown resistor allowing the V_BUS pin to float. When the
V_BUS pin is floating the audio switches are ON.
Note: Whenever the audio switches are ON the USB
transceivers connected at D- and D+ (pins 8 and 9) need to
be in the high impedance state or static high or low state to
keep from interfering with the audio transmission.
For the ISL54402 part the NC1 audio switch is active (turned
ON) whenever logic pin IN1 (pin 10) is LOW. The NC2 audio
switch is active (turned ON) whenever the logic pin IN2
(pin 2) is LOW. Unlike the ISL54400 and ISL54401 parts
FN6240.3
July 12, 2006