Datasheet

LTC6602
20
6602fc
APPLICATIONS INFORMATION
Figure 13. Two Filters in a Master/Slave Configuration
If the lowpass cutoff frequency varies then the Figure 12b
circuit must be used.
The output common mode voltage is equal to the voltage
of the V
OCM
pin. The V
OCM
pin is biased to one half of the
supply voltage by an internal resistive divider (see Block
Diagram). To alter the common mode output voltage, V
OCM
can be driven with an external voltage source or resistor
network. If external resistors are used, it is important to
note that the internal 1.6k resistors can vary ±30% (their
ratio varies only ±1%). The filter outputs can also be AC
coupled.
The LTC6602 can be interfaced to an A/D converter by pull-
ing CLKCNTL (Pin 5) to V+
D
. This configures CLKIO (Pin 15)
as a clock output, which can be used to drive the clock
input of the A/D converter. This allows the A/D converter
to be synchronized with the filter sampling clock, avoiding
“beat frequencies” and simplifying the board layout. Any
routing attached to the CLKIO pin should be as short as
possible, in order to minimize ringing.
Similarly, two LTC6602s can be connected in a master/
slave configuration as shown in Figure 13. This results
in four matched filter channels, all synchronized to the
same clock. The master has its CLKCNTL pin pulled to
V+
D
, configuring its CLKIO pin as an output, while the
slave has its CLKCNTL pin pulled to ground, configuring
its CLKIO pin as an input.
Output Drive
The filter outputs can drive 1k and/or 50pF loads connected
to AC ground with a 0.5V to 2.5V signal (corresponding
to a 4V
P-P
differential signal). For differential loads (loads
connected between +OUTA and –OUTA or +OUTB and
–OUTB) the outputs can produce a 4V
P-P
signal across 2k
and/or 25pF. For smaller signal amplitudes, the outputs can
drive correspondingly heavier loads. For larger capacitive
loads, an external 50Ω series resistor is recommended
for each output.
V+
IN
V+
A
V+
D
+INA
–INA
CLKCNTL
CLKIO
GND
LTC6602
MASTER
V
OUT1
V
IN1
0.1µF
+
–
+
–
+
–
+
–
6602 F13
+OUTA
–OUTA
R
BIAS
3.3V
LTC6602
SLAVE
V
OUT2
V
IN2
0.1µF
+OUTA
–OUTA
3.3V
V+
IN
V+
A
V+
D
+INA
–INA
CLKCNTL
CLKIO
GND
R
BIAS
R
BIAS
R
BIAS