isl54205b Intersil Corporation, isl54205b Datasheet - Page 10

• Manufacturer Part Number: isl54205b
• Description: Mp3/usb 2.0 High Speed Switch With Negative Signal Handling
• Manufacturer: Intersil Corporation

minimum edge and phase distortion to meet USB 2.0 high
speed signal quality specifications. See high-speed eye
diagram in the “Typical Performance Curves” on page 12,
Figure 12.
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
full-speed eye diagram in the “Typical Performance Curves”
on page 13, Figure 13.
The maximum signal range for the USB switches is from
-1.5V to V
allowed to exceed the V
by more than -1.5V.
The USB switches are active (turned ON) whenever the
V
low, so when V
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.
ISL54205B Operation
The discussion that follows will discuss using the ISL54205B
in the “Application Block Diagram” on page 9.
LOGIC CONTROL
The state of the ISL54205B device is determined by the
voltage at the VBUS pin (pin 2) and the CTRL pin (pin 10).
Refer to “Truth Table” on page 2.
The VBUS pin and CTRL pin are internally pulled low
through 4M
CTRL control pin is only active when V
Logic Control Voltage Levels:
V
Floating.
V
CTRL = Logic “0” (Low) when
CTRL = Logic “1” (High) when
Audio Mode
If the VBUS pin = Logic “0” 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
switches are OFF (high impedance). In a typical application,
V
connected to the battery or LDO of the MP3 player or cell
phone. When a headphone is plugged into the common
connector, nothing gets connected at the VBUS pin (it is
floating) and as long as the CTRL = Logic “1,” the
ISL54205B part remains in the audio mode and the audio
drivers of the player can drive the headphones and play
music.
BUS
BUS
BUS
DD
will be in the range of 2.7V to 3.6V and will be
voltage is
= Logic “0” (Low) when V
= Logic “1” (High) when V
DD
Ω
. The signal voltage at D- and D+ should not be
resistors to ground and can be left floating. The
BUS
≥
to V
is floating, the USB switches are OFF.
DD
DD
+ 0.8V. V
voltage rail or go below ground
10
≤
≥
BUS ≤
0.5V or floating.
BUS ≥
1.4V
BUS
V
V
BUS
is internally pulled
DD
DD
is logic “0”.
+ 0.8V
+ 0.2V or
ISL54205B
USB Mode
If the VBUS pin = Logic “1” 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 (high impedance). When a USB cable from a computer or
USB hub is connected at the common connector, the voltage at
the VBUS pin will be driven to be in the range of 4.4V to 5.25V.
The ISL54205B 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 ISL54205B
automatically turns the D+ and D- switches OFF.
Low Power Mode
If the VBUS 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.
EXTERNAL VBUS SERIES RESISTOR
The ISL54205B contains a clamp circuit between VBUS and
VDD. Whenever the VBUS voltage is greater than the VDD
voltage by more than 2.55V, current will flow through this clamp
circuitry into the V
During normal USB operation, V
3.6V and V
circuit is not active and no current will flow through the clamp
into the V
In a USB application, the situation can exist where the V
voltage from the computer could be applied at the VBUS pin
before the V
range and current will flow through the clamp into the V
power supply bus. This current could be quite high when V
OFF or at 0V and could potentially damage other components
connected in the circuit. In the application circuit, a 22k
resistor has been put in series with the VBUS pin to limit the
current to a safe level during this situation.
It is recommended that a current limiting resistor in the range of
10k
have minimal impact on the logic level at the VBUS 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
V
POWER
The power supply connected at VDD (pin 1) provides power to
the ISL54205B part. Its voltage should be kept in the range of
2.7V to 3.6V when used in a USB/Audio application to ensure
you get proper switching when the V
lower limit of 4.4V.
BUS
Ω
to 50k
will not exceed V
DD
BUS
Ω
DD
supply.
be connected in series with the VBUS pin. It will
voltage is up to its normal operating voltage
is in the range of 4.4V to 5.25V. The clamp
DD
power supply bus.
DD
by more than 2.55V.
DD
is in the range of 2.7V to
BUS
voltage is at its
September 25, 2007
Ω
DD
FN6557.0
BUS
DD
is