ISL54206A_1010 Datasheet, PDF (10/20 Pages) Intersil Corporation – MP3/USB 2.0 High Speed Switch with Negative Signal Handling

ISL54206A
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 (0.707V_RMS) 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, Figures 9, Figures 10, and
Figures 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 ≤0.5V and the CTRL voltage to ≥1.4V.
Note: Whenever the audio switches are ON, the USB
transceivers need to be in the high impedance state or
static high or low state.
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 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
high-speed eye diagram 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, Figures 12 thru 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 allowed 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 ≥1.4V.
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.
USB Switch Cell Off-Isolation
Due to the unique internal architecture of the ISL54206A
part, the USB switch cell has limited off-isolation to a
negative signal at the COM side of the part.
When driving an audio signal into the L and R inputs a
small negative voltage will appear at the D- and D+ lines
as the audio signal transitions below ground. With a USB
transceiver connected at the D-/D+ pins and with a 32Ω
headphone connected at the COM pins Table 1 shows the
negative voltage generated at the D-/D+ lines as you
increase the audio amplitude across the headphone load.
AUDIO SIGNAL
AMPLITUDE
800mV_P-P
880mV_P-P
1.08V_P-P
2V_P-P
2.25V_P-P
4V_P-P
TABLE 1.
D-/D+ VOLTAGE (V)
+25°C
+85°C
-0.22
-0.27
-0.24
-0.3
-0.3
-0.34
-0.41
-0.44
-0.47
-0.5
-0.83
-0.85
The USB specification (USB Specification Rev 2.0,
Chapter 7, Section 7.1.1) states that a USB transceiver
must be able to tolerate a -1V signal at its D-/D+
differential inputs. The data in the table shows that the
-1V level is never exceeded during audio operation and
should have no impact on the long-term reliability of
the USB transceiver.
ISL54206A Operation
The following discussion discusses using the ISL54206A
in the typical application shown in the block diagrams
on page 9.
V_DD 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 ISL54206A 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. 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 left floating or tri-stated by
10
FN6515.3
October 28, 2010