ISL54405IRTZ-T Intersil, ISL54405IRTZ-T Datasheet - Page 11

• Manufacturer Part Number: ISL54405IRTZ-T
• Description: IC MUX STEREO 2:1 CD/MP3 16-TQFN
• Manufacturer: Intersil

Specifications of ISL54405IRTZ-T

• Function: Switch
• Circuit: 2 x SPDT
• Voltage Supply Source: Single Supply
• Voltage - Supply, Single/dual (±): 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

COM side (L,R) are activated and inoperable on the signal
side (L1, R1, L2, R2) of the switch. When DIR_SEL = Logic
“0” the C/P shunts are activated on the signal side (L1, R1,
L2, R2) and inoperable on the COM side (L, R).
Logic Levels:
AC/DC, DIR_SEL = Logic “0” (Low) when
AC/DC, DIR_SEL = Logic “1” (High) when
The AC/DC and DIR_SEL have internal pull-up resistors to
the internal 3.3V supply rail and can be driven high or
tri-stated (floated by the µprocessor). They should be driven
to ground for a logic “0” (Low). Note: For 5V applications, the
AC/DC and DIR_SEL pins should never be driven to the
external 5V rail. They need to be driven with 1.8V logic or 3V
logic circuit.
AC Coupled or DC Coupled Operation
The Audio CODEC drivers can be directly coupled to the
ISL54405 when the audio signals from the drivers are
ground referenced or do not have a significant DC offset
voltage, < 50mV. Otherwise the signal should be AC coupled
to the ISL54405 part.
CLICK AND POP OPERATION
The ISL54405 has special circuitry to eliminate click and
pops in the speakers during power-up and power-down of
the Audio CODEC Drivers and during removal and insertion
of headphones.
A different click and pop scheme is required depending on
whether the audio CODEC drivers are AC coupled or DC
coupled to the inputs of the ISL54405 part.
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 down of the driver a transient can be
coupled into the speaker load through the DC blocking
capacitor (see the “Application Block Diagrams” on page 8).
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 Audio mode or there is no
low impedance path to discharge the capacitor voltage at the
input of the switch, before turning on the switch, a transient
discharge will occur in the speaker, generating a Click and
pop noise.
Proper elimination of a click/pop transient at the speaker
load while powering up or down of the audio driver requires
that the ISL54405 have its C/P shunts activated on the
source side of the switch and then placed in Mute mode.
This allows the transient generated by the audio drivers to
be discharged through the Click and Pop shunt circuitry.
11
≤
≥
0.5V
1.4V or Floating.
ISL54405
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 C/P shunt circuitry,
the switches can be turned ON and connected through to the
speaker loads without generating an undesirable click/pop in
the speakers.
With a typical DC blocking capacitor of 220µF and the C/P
shunt circuitry designed to have a resistance of 40Ω,
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 25 and 26 in the “Typical Performance Curves”
beginning on page 13.
DC COUPLED CLICK AND POP OPERATION
The ISL54405 can pass ground referenced audio signals
which allows it to be directly connected to audio drivers that
output ground referenced audio signals, eliminating the need
for a DC blocking capacitor.
Audio drivers that swing around ground however do
generate some DC offset, from a few millivolts to tens of
millivolts. When switching between audio channels or muting
the audio signal these small DC offset levels of the drivers
can generate a transient that can cause un-wanted clicks
and pops in the speaker loads.
In a DC coupled application the C/P shunt resistors placed at
the source side of the switch have no effect in eliminating the
transients at the speaker loads when transitioning in and out
of the mute state or switching between channels. In fact
having these C/P shunts active on the source side only
increase un-neccesary power consumption. So, for DC
coupled connection the C/P shunt circuitry should not be
applied at the source (driver) side of the switch.
For DC coupled applications the ISL54405 has a special
soft-start feature that slowly ramps the DC offset voltage
from the audio driver to the speaker load when turning ON a
switch channel. The ramp rate at the load is determined by
the capacitor value connected at the CAP_SS pin.
Lab experimentation has shown that if you can slow the
voltage ramp rate at the speaker to < 10V/s, you can
eliminate click/pop noise in a speaker. A soft-start capacitor
value of 0.1µF provides for 4.5V/s ramp rate and is
recommended. See Figures 27 and 28 in the “Typical
Performance Curves” beginning on page 13.
See “MUTE to ON” section on page 10 for more detail of
how soft-start works.
Supply Sequencing and Overvoltage Protection
With any CMOS device, proper power supply sequencing is
required to protect the device from excessive input currents
which might permanently damage the IC. All I/O pins contain
ESD protection diodes or diode stacks from the pin to V
and to GND (see Figure 8). To prevent forward biasing these
June 5, 2008
FN6699.1
DD