9

November 25, 2008

data connector into a single shared connector, thereby

saving space and component cost. “Typical Application

Block Diagrams” on page 8 of this functionality are shown in

Figures 8 and 9.

The ISL54215 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

cellular phone. The ISL54215 also contains a logic control

pin (CTRL) that when driven Low while IN is Low, opens all

switches and puts the part into a low power state, drawing

Detailed descriptions of the two types of switches are

provided in the following sections.

Audio Switches

The two audio switches (L, R) are 2.5

Ω 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 over a ±1V

signal range.

Crosstalk between the audio channels is -100dB over the

audio band. Crosstalk between the audio channel and USB

channel is -95dB at 100kHz. These switches have excellent

OFF-isolation, 115dB, over the audio band with a 32

Ω load.

variation. They can pass ground referenced audio signals with

very low distortion (<0.05% THD+N) when delivering 15.6mW

into a 32

Ω headphone speaker load. See Figures 10 through

13 for THD+N performance curves.

These switches are bi-directional switches. In typical

applications, the audio drivers would be connected at the L

and R side of the switch (pins 6 and 7) and the speaker

loads would be connected at the COM side of the switch

(pins 3 and 4).

The audio switches are active (turned ON) whenever the IN

voltage is

≤ 0.5V or floating and the CTRL voltage ≥ to 1.4V.

USB Switches

The two USB switches (D+, D-) are bidirectional switches

that can pass rail-to-rail signals. When powered with a 3.3V

signal range is only 0.05

Ω ensuring minimal impact by the

switches to USB high speed signal transitions. As the signal

level of 3.3V, the switch resistance is nominally 25

Ω.

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 Figure 14.

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 Figure 15

for Full-speed Eye Pattern taken with switch in the signal path.

The maximum signal range for the USB switches is from

by more than -1.5V.

The USB switches are active (turned ON) whenever the IN

voltage is

≥ to 1.4V.

ISL54215 Operation

The following will discuss using the ISL54215 in the “Typical

Application Block Diagrams” on page 8 shown in Figures 8

and 9.

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 5.0V.

In a typical USB/Audio application for portable 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

a USB data signal level above 2.5V.

LOGIC CONTROL

The state of the ISL54215 device is determined by the

voltage at the IN pin (pin 2) and the CTRL pin (pin 10).

the range of 2.7V to 3.6V and can be controlled by a

standard microprocessor. The part has three states or

modes of operation. The Audio Mode, USB Mode and the

Low Power Mode. Refer to the “Truth Table” on page 2.

The IN and CTRL pins are internally pulled low through a

4M

Ω resistor to ground and can be left floating or tri-stated

by the µprocessor. The CTRL control pin is only active when

IN is logic “0”.

Logic control voltage levels:

CTRL = Logic “0” (Low) when

≤ 0.5V or Floating.

CTRL = Logic “1” (High) when

≥ 1.4V

Audio Mode

If the IN 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) 2.5

Ω audio switches are ON and the D- and D+ 5Ω

switches are OFF (high impedance).

ISL54215