MAX7490 Maxim, MAX7490 Datasheet - Page 14

• Manufacturer Part Number: MAX7490
• Description: Dual Universal Switched-Capacitor Filters
• Manufacturer: Maxim

Dual Universal Switched-Capacitor Filters
Mode 3A Design Equations
Note: When the passband gain error exceeds 1dB, the
use of capacitor C
the inverting input will reduce the gain error. The value
can best be determined experimentally. Typically, it
should be about 5pF/dB (C
14
Table 3. Suggested External Op Amps
Figure 8. Block Diagram of a 2nd-Order Section Showing the Input Offsets
______________________________________________________________________________________
MAX4281
MAX4322
MAX4130
MAX4490
PART
f
f
Q
H
H
H
H
H
O
n
OHP
OLP
OBP
ON
ON
=
=
=
1
R
R
2
f
f
100
CLK
100
(
CLK
2
(
3
f
=
=
at f
=
→
−
−
−
R
R
R
R
R
R
R
R
C
0
=
1
1
1
INV
COM
4
4
2
2
3
Hz
R
R
R
f
between the lowpass output and
R
CLK
H
4
L
2
)
=
V
OS1
R
/ )
R
C-MAX
2
G
L
GBW (MHz)
=



R
R
R
R
4
10
10
1
G
H
2
5
= 15pF).






R
R
2
1



N/HP
+
SLEW RATE (V/µs)
Σ
S
-
10.0
0.7
2.0
4.0
V
OS2
Switched-capacitor integrators generally exhibit higher
input offsets than discrete RC integrators. The larger
offset is mainly due to the charge injection of the
CMOS switches into the integrating capacitors. The
internal op amp offset also adds to the overall offset
value. Figure 8 shows the input offsets from a single
2nd-order section. Table 4 lists the formula for the out-
put offset voltage for various modes and output pins.
The MAX7490 operates from a single +5V supply, and
the MAX7491 operates from a single +3V supply.
Bypass V
V
age analog supplies. If dual supplies are required,
connect the COM pin to the system ground and the
GND pin to the negative supply. Figure 9 shows an
example of dual-supply operation. Single-supply and
dual-supply performances are equivalent. For dual-
supply operation, drive CLK, SHDN, and EXTCLK from
GND (which is now V-) to V
oscillator in dual-supply mode, C
to either GND or the actual ground voltage. Use the
MAX7490 for ±2.5V and use the MAX7491 for ±1.5V.
For most applications, a 0.1µF bypass capacitor from
COM to GND is sufficient. If the V
cant 60Hz energy, increase this capacitor to 1µF or
greater to provide better power-supply rejection.
DD
∫
should be isolated from other digital or high-volt-
DD
I SUPPLY/AMP (mA)
BP
to GND with at least a 0.1µF capacitor.
V
OS3
1.15
0.5
1.1
2.0
∫
DD
LP
. If using the internal
DD
OSC
Power Supplies
Offset Voltage
supply has signifi-
PIN-PACKAGE
can be returned
5 SOT23
5 SOT23
5 SOT23
5 SOT23