ISL54065_0911 Datasheet, PDF (10/15 Pages) Intersil Corporation – Negative Signal Swing, Sub-ohm, Dual SPDT

ISL54065
on/off transients are AC coupled by the 220µF capacitor to
the speaker load causing a click and pop noise.
The ISL54065 has shunt switches on the NO and NC pins to
eliminate click and pop transients (see Figure 10). These
switches are driven complimentary to the main switch. When
NC is connected to COM, the shunt switch is active on the
NO pin (and vice versa). The shunt switches connect an
impedance (140Ω typical, see Figure 25) from the NO/NC
pin to ground to discharge any transients that may appear on
the NO or NC pins.
When the DC bias becomes active at the source, the NO
and NC terminals will also have a DC offset due to capacitor
dv/dt principle. The DC offset will be discharged through the
shunt impedance on the NO and NC terminals instead of the
speaker, eliminating click and pop noise. On the ISL54065,
the Click and Pop Circuitry is enabled when the CP pin is
logic high (>1.4V). The Click and Pop Circuitry may be
disabled by tying the CP pin low (<0.4V).
*Under high impedance loads (20kΩ) such as the input
impedance of pre-amplifiers, the COM terminal voltage may
rise due to small leakage currents charging the COM
capacitance. This is not seen when low impedance (32Ω)
loads such as headphones are used because the small
leakage currents does not result in significant potential drop
across the load. If the user desires to reduce the voltage
build up on the COM pin, a 1kΩ to ground may be placed on
the COM pin. This impedance is small enough to reduce the
voltage build up significantly while not increasing the power
dissipation dramatically. Current consumption considerations
will need to be taken for driving a smaller load impedance
under this scenario.
AUDIO
SOURCE A
220µF
NO
V+
C
R_SH
NC
220µF
AUDIO
SOURCE B
R_SH
COM
R_L
32Ω
EN
CP
µP
IN
GND
ISL54065
FIGURE 10. CLICK AND POP OPERATION
Click and Pop with Enable Pin
Click and pop elimination can be driven with the Enable pin
by setting it low. Having the Enable pin low turns OFF the
main switches (NO and NC) while the Click and Pop
Circuitry will be active. Transient voltages due to power
on/off from both sources will be shunted to ground. For
proper Click and Pop Elimination the Enable pin should be
driven high at least 200ms after any source transients occurs
to avoid audible transients at the speaker load.
Click and Pop with Input Select Pin
Click and pop elimination can also be driven with the Input
Select pin. When INx = 0, the NOx terminals are connected
to the shunt impedance. When INx = 1, the NCx terminals
are connected to the shunt impedance. In this situation, only
one of the source transient voltages will be shunted to
ground, depending on the Input Select state. The Input
Select pin should be driven 200ms after any source
transients occurs to prevent audible transients at the
speaker load.
Logic-Level Thresholds
This switch family is 1.8V CMOS compatible (0.45V V_OLMAX
and 1.35V V_OHMIN) over a supply range of 1.8V to 3.3V
(see Figure 16). At 3.3V the V_IL level is 0.5V maximum. This
is still below the 1.8V CMOS guaranteed low output
maximum level of 0.45V, but noise margin is reduced. At
3.3V the V_IH level is 1.4V minimum. While this is above the
1.8V CMOS guaranteed high output minimum of 1.35V
under most operating conditions the switch will recognize
this as a valid logic high.
The digital input stages draws a larger supply current
whenever the digital input voltage is not at one of the supply
rails. Driving the digital input signals from GND to V+ with a
fast transition time minimizes power dissipation. The
ISL54065 has been designed to minimize the supply current
whenever the digital input voltage is not driven to the supply
rails (0V to V+). For example driving the device with 2.85V
logic high while operating with a 4.2V supply the device
draws only 1µA of current.
High-Frequency Performance
In 50Ω systems, the ISL54065 has an ON switch -3dB
bandwidth of 60MHz (see Figure 21). The frequency
response is very consistent over a wide V+ range, and for
varying analog signal levels.
An OFF switch acts like a capacitor across the open
terminals and AC couples higher frequencies, resulting in
signal feed-through from a switch’s input to its output.
Off-Isolation is the resistance to this feed-through. Crosstalk
indicates the amount of feed-through from one switch
channel to another switch channel. Figure 22 details the high
Off-Isolation and Crosstalk rejection provided by this part. At
100kHz, Off-Isolation is about 60dB in 50Ω systems,
decreasing approximately 20dB per decade as frequency
10
FN6583.2
November 3, 2009