ISL54212 Datasheet, PDF (9/15 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

ISL54212
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
minimum edge and phase distortion to meet USB 2.0 high
speed signal quality specifications. See the high-speed eye
diagram in Figure 15.
The USB switches can also pass USB full-speed signals
(12Mbps) with minimal distortion and meet all the USB
requirements for USB 2.0 full-speed signaling. See the
full-speed eye diagrams in Figures 12, 13 and 14.
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 ≤0.5V.
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.
ISL54212 Operation
The sections that follow will discuss using the ISL54212 in the
typical application shown in the block diagram on page 8.
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 2.5V 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 ≥2.5V in order to get
a USB data signal level above 2.5V.
LOGIC CONTROL
The state of the ISL54212 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 the 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 µprocessor.
The CTRL pin is internally pulled low through a 4MΩ resistor to
ground and can be tri-stated by the µprocessor. The CTRL
control pin is only active when IN is logic “1”.
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.
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 “1” and CTRL pin = Logic “1,” the part
will be in the Audio mode. In Audio mode the L (left) and R
(right) 3Ω audio switches are ON and the D- and D+ 5Ω USB
switches are OFF.
When nothing is plugged into the common connector or a
headphone is plugged into the common connector, the
µprocessor 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 ISL54212 high. As long as the CTRL = Logic “1,” the
ISL54212 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 “0” and CTRL pin = Logic “0” or Logic “1”
the part will go into USB mode. In USB mode, the D- and D+
5Ω switches are ON and the L and R 3Ω audio switches are
OFF.
When a USB cable from a computer or USB hub is
connected at the common connector, the µprocessor will
sense the presence of the 5V V_BUS and drive the IN pin
voltage low. The ISL54212 part will go into the USB mode. In
USB mode, the computer or USB hub transceiver and the
MP3 player or cell phone USB transceiver are connected
and digital data will be able to be transmitted back and forth.
When the USB cable is disconnected, the μprocessor will
sense that the 5V V_BUS voltage is no longer connected and
will drive the IN pin high and put the part back into the Audio
or Low Power mode.
Low Power Mode
If the IN pin = Logic “1” and CTRL pin = Logic “0,” the part will
be in the Low Power mode. In the Low Power mode, the audio
switches and the USB switches are OFF. In this state, the
device draws typically 1nA of current.
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FN6556.0
September 18, 2007