ISL54206 Datasheet, PDF (9/13 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

ISL54206
When a USB cable from a computer or USB hub is
connected at the common connector, the μprocessor will
sense the present of the 5V VBUS and drive the IN pin
voltage high. The ISL54206 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 VBUS voltage is no longer connected and
will drive the IN pin low and put the part back into the Audio
or Low Power Mode.
Low Power Mode
If the IN pin = Logic “0” 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 (high impedance). In
this state, the device draws typically 1nA of current.
USING THE COMPUTER VBUS VOLTAGE TO DRIVE THE
“IN” PIN
External IN Pull-Down Resistor
Rather than using a micro-processor to control the IN logic
pin you can directly drive the IN pin using the VBUS voltage
from the computer or USB hub. In order to do this you must
connected an external resistor from the IN pin to ground.
When a headphone or nothing is connected at the common
connector the external pull-down will pull the IN pin low
putting the ISL54206 in the Audio mode or Low Power mode
depending on the condition of the CTRL pin.
When a USB cable is connected at the common connector
the voltage at the IN pin will be driven to 5V and the part will
automatically go into the USB mode.
When the USB cable is disconnected from the common
connector the voltage at the IN pin will be pulled low by the
pull-down resistor and return to the Audio Mode or Low
Power Mode depending on the condition of the CTRL pin.
Note: The voltage at the IN pin can exceed the VDD voltage
by as much as 2.55V. This allows the VBUS voltage from a
computer or USB hub (4.4V to 5.25V) to drive the IN pin
while the V_DD voltage is in the range of 2.7V to 3.6V.
External IN Series Resistor
The ISL54206 contains a clamp circuit between IN and VDD.
Whenever the IN voltage is greater than the V_DD voltage by
more than 2.55V, current will flow through this clamp circuitry
into the V_DD power supply bus.
During normal USB operation, V_DD is in the range of 2.7V to
3.6V and IN (VBUS voltage from computer or USB hub) is in
the range of 4.4V to 5.25V, the clamp circuit is not active and
no current will flow through the clamp into the V_DD supply.
In a USB application, the situation can exist where the V_BUS
voltage from the computer could be applied at the IN pin
before the V_DD voltage is up to its normal operating voltage
range and current will flow through the clamp into the V_DD
power supply bus. This current could be quite high when
V_DD is OFF or at 0V and could potentially damage other
components connected in the circuit. In the application
circuit, a 22kΩ resistor has been put in series with the IN pin
to limit the current to a safe level during this situation.
It is recommended that a current limiting resistor in the range
of 10kΩ to 50kΩ be connected in series with the IN pin. It will
have minimal impact on the logic level at the IN pin during
normal USB operation and protect the circuit during the time
VBUS is present before VDD is up to its normal operating
voltage.
Note: No external resistor is required in applications where
the voltage at the IN pin will not exceed V_DD by more than
2.55V.
9
FN6409.0
December 18, 2006