ISL54205B Datasheet, PDF (9/16 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

ISL54205B
Application Block Diagram
22kΩ
V_BUS
COM -
V_DD
ISL54205B
LOGIC CIRCUITRY
4MΩ
4MΩ
CTRL
D-
D+
COM +
50kΩ L
R
50kΩ
GND
µCONTROLLER
USB
HIGH-SPEED
TRANSCEIVER
CODEC
Detailed Description
The ISL54205B device is a dual single pole/double throw
(SPDT) analog switch device that operates from a single DC
power supply in the range of 2.7V to 3.6V. It was designed to
function as a dual 2 to 1 multiplexer to select between USB
differential data signals and audio L and R stereo signals. It
comes in tiny µTQFN and TDFN packages for use in MP3
players, PDAs, cell phones, and other personal media
players.
The part consists of two 3Ω audio switches and two 5Ω 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
high-speed USB differential data signals with minimal edge
and phase distortion.
The ISL54205B was specifically designed for MP3 players,
cell phones and other personal media player 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. See “Application Block
Diagram” on page 9.
The ISL54205B incorporates 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 cell phone. The ISL54205B contains a logic control
pin (CTRL) that when driven low while V_BUS is low, opens all
switches and puts the part into a low power state, drawing
typically 1nA of I_DD current.
A detailed description of the two types of switches is
provided in the following sections. The USB transmission
and audio playback are intended to be mutually exclusive
operations.
9
Audio Switches
The two audio switches (L, R) are 3Ω switches that can pass
signals that swing below ground. Crosstalk between the
audio switches over the audio band is <-110dB.
Over a signal range of ±1V (0.707V_RMS) 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 32Ω headphone speaker load. See Figures 8,
9, 10, and 11 THD+N in the “Typical Performance Curves on
page 11.
These switches are uni-directional switches. The audio
drivers should be connected at the L and R 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).
The audio switches are active (turned ON) whenever the
V_BUS voltage is ≤ to V_DD + 0.2V or floating 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.
USB Switches
The two USB switches (D+, D-) are bidirectional switches
that can pass rail-to-rail signals. When powered with a 3.6V
supply these switches have a nominal r_(ON) of 4.6Ω over the
signal range of 0V to 400mV with a r_(ON) flatness of 0.4Ω.
The r_(ON) matching between the D+ and D- switches over
this signal range is only 0.06Ω ensuring minimal impact by
the switches to USB high speed signal transitions. As the
signal level increases the r_(ON) resistance increases. At
signal level of 3.3V the switch resistance is nominally 23Ω.
The USB switches were specifically designed to pass USB
2.0 high-speed (480Mbps) differential signals typically in the
range of 0V to 400mV. They have low capacitance and high
bandwidth to pass the USB high-speed signals with
FN6557.0
September 25, 2007