ISL54217_09 Datasheet, PDF (12/21 Pages) Intersil Corporation – USB 2.0 High-Speed x 2Channels/Stereo Audio Dual SP3T (Dual 3-to-1 Multiplexer)

ISL54217
Any signals connected at the USB2 signal lines will
momentarily get passed through to the COM outputs.
Delay time between C1 and C0 must be < 100ns and should
be controlled by logic control drivers with well behaved
monotonic transitions from High to Low and Low to High and
with typical logic family rise and fall times of 1ns to 6ns.
POWER
The power supply connected at VDD (pin 11) provides power
to the ISL54217 part. Its voltage should be kept in the range
of 2.7V to 4.6V. In a typical application V_DD will be in the
range of 2.7V to 4.3V and will be connected to the battery or
LDO of the MP3 player or cellphone.
A 0.01µF or 0.1µF decoupling capacitor should be
connected from the VDD pin to ground to filter out any power
supply noise from entering the part. The capacitor should be
located as close to the VDD pin as possible.
Before power-up and power-down of the ISL54217 part the
C1 and C0 control pins should be driven to ground or
tri-stated. This will put the switch in the ALL SWITCHES
OFF state, which turns all switches OFF and activate the
click and pop circuitry. This will minimize transients at the
speaker loads during power-up and power-down of the
ISL54217 device. See Figure 32 in the “Typical Performance
Curves” section.
AC COUPLED CLICK AND POP OPERATION
Single supply audio drivers have their signal biased at a DC
offset voltage, usually at 1/2 the DC supply voltage of the
driver. As this DC bias voltage comes up or goes down
during power-up or power-down of the driver, a transient can
be coupled into the speaker load through the DC blocking
capacitor (see the “Block Diagram” on page 9).
When a driver is OFF and suddenly turned ON the rapidly
changing DC bias voltage at the output of the driver will
cause an equal voltage at the input side of the switch due to
the fact that the voltage across the blocking capacitor cannot
change instantly. If the switch is in the Audio mode or there is
no low impedance path to discharge the blocking capacitor
voltage, before turning the audio switch ON, a transient
discharge will occur in the speaker, generating a click/pop
noise.
Proper elimination of a click/pop transient at the speaker
loads while powering up or down of the audio drivers
requires that the ISL54217 have its click/pop circuitry
activated by putting the part in the ALL SWITCHES OFF
mode. This allows the transients generated by the audio
drivers to be discharged through the click and pop shunt
circuitry.
Once the driver DC bias has reached VDD/2 and the
transient on the switch side of the DC blocking capacitor has
been discharged to ground through the click/pop shunt
circuitry, the audio switches can be turned ON and
connected through to the speaker loads without generating
any undesirable click/pop noise in the speakers.
With a typical DC blocking capacitor of 220µF and the
click/pop shunt circuitry designed to have a resistance of
20Ω to 70Ω, allowing a 100ms wait time to discharge the
transient before placing the switch in the Audio mode will
prevent the transient from getting through to the speaker
load. See Figures 30 and 31 in the “Typical Performance
Curves” section.
Typical Performance Curves T_A = +25°C, Unless Otherwise Specified
2.95
2.90
I_COM = 60mA
2.85
2.60
I_COM = 60mA
2.58
2.80
2.75
2.70
2.65
2.60
V_DD = 2.7V
2.55
2.50
V_DD = 3.6V
2.45
V_DD = 4.6V
-1.5
-1.0
-0.5
0
0.5
1.0
1.5
V_COM (V)
FIGURE 10. AUDIO ON-RESISTANCE vs SUPPLY VOLTAGE vs
SWITCH VOLTAGE
2.56
2.54
V_DD = 3.0V
V_DD = 3.3V
V_DD = 3.6V
2.52
V_DD = 4.0V
2.50
2.48
-1.5
-1.0
V_DD = 4.6V
-0.5
0
0.5
V_COM (V)
1.0
1.5
FIGURE 11. AUDIO ON-RESISTANCE vs SUPPLY VOLTAGE vs
SWITCH VOLTAGE
12
FN6817.3
May 4, 2009