ISL54205A Datasheet, PDF (8/14 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

ISL54205A
Application Block Diagram
22kΩ
V_BUS
COM -
V_DD
ISL54205A
LOGIC CIRCUITRY
4MΩ
4MΩ
CTRL
D-
D+
COM +
50kΩ L
R
50kΩ
GND
μCONTROLLER
USB
HIGH-SPEED
TRANSCEIVER
CODEC
Detailed Description
The ISL54205A 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 ISL54205A 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. A typical application
block diagram of this functionality is shown above.
The ISL54205A 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 ISL54205A 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 sections below. The USB transmission and
audio playback are intended to be mutually exclusive
operations.
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 (0.707Vrms) 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 32Ω headphone speaker load. See Figures 8,
9, 10, and 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
(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 or static
high or low state.
USB Switches
The two USB switches (D+, D-) are 5Ω bidirectional switches
that are designed to pass high-speed USB differential
signals in the range of 0V to 400mV. The 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 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
allowed to exceed the V_DD voltage rail or go below ground
by more than -1.5V.
8
FN6342.1
December 7, 2006