ISL54212 Datasheet, PDF (8/15 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

Application Block Diagram
ISL54212
VBUS
IN
COM-
VDD
ISL54212
LOGIC CIRCUITRY
4MΩ
CTRL
D-
D+
COM+
50kΩ L
R
50kΩ
GND
LOGIC CONTROL VIA MICRO-PROCESSOR
µCONTROLLER
USB
HIGH-SPEED
TRANSCEIVER
CODEC
Detailed Description
The ISL54212 device is a dual single pole/double throw
(SPDT) analog switch device that can operate from a single
DC power supply in the range of 2.5V to 5.5V. 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 ISL54212 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. Typical application block
diagram of this functionality is shown above.
The ISL54212 has a single logic control pin (IN) that selects
between the audio switches and the USB switches. This pin
can be driven Low or High to switch between the audio
CODEC drivers and USB transceiver of the MP3 player or
cellphone. The ISL54212 also contains a logic control pin
(CTRL) that when driven Low while IN is High, opens all
switches and puts the part into a low power state, drawing
typically 1nA of I_DD current.
8
A detailed description of the two types of switches is
provided in the sections following. 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 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 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
(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 ≥1.4V and the CTRL voltage to ≥1.4V.
Note: Whenever the audio switches are ON the USB
transceivers need to be in the high impedance.
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
FN6556.0
September 18, 2007