Datasheet

13Maxim Integrated
Digitally-Programmed, Dual
2nd-Order Continuous Lowpass Filter
MAX270/MAX271
Applications Information
Power-Supply Configurations
The MAX270/MAX271 power supplies must be properly
bypassed. Best performance is achieved if V+ and V- are
bypassed to GND with 4.7µF electrolytic (tantalum is pre-
ferred) and 0.1µF ceramic capacitors in parallel. These
should be as close as possible to the chip supply pins.
Single supplies in the range of 4.75V to 16V may be
used to power the MAX270/MAX271 as shown in Figure
4. Digital logic may be referenced to V- (system ground),
but will not maintain TTL compatibility. CMOS (rail-to-
rail) logic recommended. For µP-mode operation with a
single supply, the MAX270 A0 pin must be configure with
a voltage divider (Figure 4).
Lowest quiescent current in shutdown mode is achieved
when A0 is either at V+ or V-.
Independent f
C
Programming Without a µP
Figure 6 shows how filter sections A and B may be pro-
grammed to different cutoff frequencies without the use
of a µP. The MAX690 µP supervisory circuit provides the
proper programming sequence when the circuit is pow-
ered up by controlling the 74HC373 data buffer and the
MAX270 addressing pin to load independent f
C
data for
filters A and B.
Figure 4. Power-Supply Configurations
V+
A0
(MAX270)
SINGLE-SUPPLY OPERATION
GND
V-
4.7kI
10kI
PIN-STRAP
MODE
µP
MODE
0V
+5V
+5V
10k
I
4.7kI 4.7µF 0.1µF
0.1µF
4.7µF
+5V
MAX270
V+
BIPOLAR-SUPPLY OPERATION
GND
V-
4.7µF 0.1µF
0.1µF
4.7µF
+5V
-5V
MAX270
MAX271