19-1416; Rev 0; 1/99
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
General Description
The MAX7480 8th-order, lowpass, Butterworth,
switched-capacitor filter (SCF) operates from a single
+5V supply. The device draws only 2.9mA of supply
current and allows corner frequencies from 1Hz to
2kHz, making it ideal for low-power post-DAC filtering
and anti-aliasing applications. The MAX7480 features a
shutdown mode, which reduces the supply current to
0.2µA.
Two clocking options are available: self-clocking
(through the use of an external capacitor) or external
clocking for tighter corner-frequency control. An offset
adjust pin allows for adjustment of the DC output level.
The MAX7480 Butterworth filter provides a maximally
flat passband response. The fixed response simplifies
the design task to selecting a clock frequency.
Features
o
8th-Order, Lowpass Butterworth Filter
o
Low Noise and Distortion: -73dB THD + Noise
o
Clock-Tunable Corner Frequency (1Hz to 2kHz)
o
100:1 Clock-to-Corner Ratio
o
+5V Single-Supply Operation
o
Low Power
2.9mA (Operating Mode)
0.2µA (Shutdown Mode)
o
Available in 8-Pin SO/DIP Package
o
Low Output Offset:
±5mV
MAX7480
Applications
ADC Anti-Aliasing
Post-DAC Filtering
PART
MAX7480ESA
MAX7480EPA
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 SO
8 Plastic DIP
Pin Configuration
TOP VIEW
V
SUPPLY
COM
1
IN
2
8
7
CLK
SHDN
OS
OUT
INPUT
0.1µF
Typical Operating Circuit
V
DD
IN
SHDN
OUT
OUTPUT
MAX7480
GND
3
6
5
V
DD
4
MAX7480
SO/DIP
CLOCK
CLK
GND
COM
OS
0.1µF
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
MAX7480
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ..............................................................-0.3V to +6V
IN, OUT, COM, OS, CLK ............................-0.3V to (V
DD
+ 0.3V)
SHDN........................................................................-0.3V
to +6V
OUT Short-Circuit Duration...................................................1sec
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SO (derate 5.88mW/°C above +70°C)................471mW
8-Pin DIP (derate 9.09mW/°C above +70°C) ...............727mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,
SHDN
=
V
DD
, f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
FILTER CHARACTERISTICS
Corner Frequency
Clock-to-Corner Ratio
Clock-to-Corner Tempco
Output Voltage Range
Output Offset Voltage
DC Insertion Gain with
Output Offset Removed
Total Harmonic Distortion
plus Noise
OS Voltage Gain to OUT
Input Voltage Range at OS
THD+N
A
OS
V
OS
Input, COM externally driven
COM Voltage Range
V
COM
Output, COM internally biased
Input Resistance at COM
Clock Feedthrough
Resistive Output Load Drive
Maximum Capacitive Load at
OUT
Input Leakage Current at COM
Input Leakage Current at OS
CLOCK
Internal Oscillator Frequency
Clock Input Current
Clock Input High
Clock Input Low
f
OSC
I
CLK
V
IH
V
IL
C
OSC
= 1000pF (Note 4)
V
CLK
= 0 or 5V
V
DD
- 0.5
0.5
40
53
±24
67
±40
kHz
µA
V
V
R
L
C
L
SHDN
= GND, V
COM
= 0 to V
DD
V
OS
= 0 to (V
DD
- 1V) (Note 3)
10
50
R
COM
V
DD
/ 2
- 0.5
V
DD
/ 2
- 0.2
75
V
OFFSET
V
IN
= V
COM
= V
DD
/ 2
V
COM
= V
DD
/ 2 (Note 2)
f
IN
= 200Hz, V
IN
= 4Vp-p,
measurement bandwidth = 22kHz
-0.1
0.25
±5
0.15
-73
1
V
COM
±0.1
V
DD
/ 2 V
DD
/ 2
+ 0.5
V
V
DD
/ 2 V
DD
/ 2
+ 0.2
125
10
1
500
±0.1
±0.1
±10
±10
kΩ
mVp-p
kΩ
pF
µA
µA
f
C
f
CLK
/ f
C
(Note 1)
0.001 to 2
100:1
10
V
DD -
0.25
±25
0.3
ppm/°C
V
mV
dB
dB
V/ V
V
kHz
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF from COM to GND,
SHDN
=
V
DD
, f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
POWER REQUIREMENTS
Supply Voltage
Supply Current
Shutdown Current
Power-Supply Rejection Ratio
SHUTDOWN
SHDN
Input High
SHDN
Input Low
SHDN
Input Leakage Current
V
SDH
V
SDL
V
SHDN
= 0 to V
DD
±0.1
V
DD
- 0.5
0.5
±10
V
V
µA
V
DD
I
DD
I
SHDN
PSRR
Operating mode, no load, IN = OS = COM
SHDN
= GND, CLK driven from 0 to V
DD
Measured at DC
4.5
2.9
0.2
60
5.5
3.5
1
V
mA
µA
dB
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX7480
FILTER CHARACTERISTICS
(V
DD
= +5V, filter output measured at OUT, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD
, V
COM =
V
OS =
V
DD
/2
,
f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
f
IN
= 0.5f
C
Insertion Gain Relative to
DC Gain
f
IN
= f
C
f
IN
= 2f
C
f
IN
= 3f
C
CONDITIONS
MIN
-0.1
-3.5
TYP
0.0
-3.0
-48
-76
-2.5
-43
-70
dB
MAX
UNITS
Note 1:
The maximum f
C
is defined as the clock frequency f
CLK
= 100
·
f
C
at which the peak SINAD drops to 68dB with a sinusoidal
input at 0.2f
C
.
Note 2:
DC insertion gain is defined as
∆V
OUT
/
∆V
IN
.
Note 3:
OS voltages above V
DD
- 1V saturate the input and result in a 75µA typical input leakage current.
Note 4:
f
OSC
(kHz)
≅
53
·
10
3
/ C
OSC
(pF).
_______________________________________________________________________________________
3
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
MAX7480
Typical Operating Characteristics
(V
DD
= +5V, f
CLK
= 100kHz,
SHDN
= V
DD
, V
COM
= V
OS
= V
DD
/ 2, T
A
= +25°C, unless otherwise noted.)
FREQUENCY RESPONSE
MAX7480 toc01
PASSBAND FREQUENCY RESPONSE
MAX7480 toc02
PHASE RESPONSE
f
C
= 1kHz
80
PHASE SHIFT (DEGREES)
160
240
320
400
480
560
MAX7480 toc03
MAX7480-09
MAX7480-06
20
0
-20
GAIN (dB)
-40
-60
-80
-100
-120
0
f
C
= 1kHz
0.5
0
-0.5
GAIN (dB)
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
f
C
= 1kHz
0
640
0
202
404
606
808
1010
0
400
800
1200
1600
2000
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT FREQUENCY (kHz)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX7480 toc04
SUPPLY CURRENT vs. TEMPERATURE
MAX7480 toc05
DC OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
2.0
V
IN
= V
COM
1.5
DC OFFSET VOLTAGE (mV)
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
3.00
NO LOAD
2.95
SUPPLY CURRENT (mA)
2.90
2.85
2.80
2.75
2.70
3.00
NO LOAD
2.95
SUPPLY CURRENT (mA)
2.90
2.85
2.80
2.75
2.70
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
SUPPLY VOLTAGE (V)
-40
-20
0
20
40
60
80
100
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
OFFSET VOLTAGE vs. TEMPERATURE
MAX7401 toc07
INTERNAL OSCILLATOR FREQUENCY vs.
C
OSC
CAPACITANCE
MAX7480 toc08
NORMALIZED INTERNAL OSCILLATOR
FREQUENCY vs. SUPPLY VOLTAGE
1.05
NORMALIZED OSCILLATOR FREQUENCY
1.04
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
0.95
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
SUPPLY VOLTAGE (V)
C
OSC
= 530pF
1.0
V
IN
= V
COM
= V
DD
/ 2
0.5
OFFSET VOLTAGE (mV)
1000
100
FREQUENCY (kHz)
0
10
-0.5
1
-1.0
0.1
-1.5
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
0.01
0.1
1
10
CAPACITANCE (nF)
100
1000
4
_______________________________________________________________________________________
8th-Order, Lowpass, Butterworth,
Switched-Capacitor Filter
Typical Operating Characteristics (continued)
(V
DD
= +5V, f
CLK
= 100kHz,
SHDN
= V
DD
, V
COM
= V
OS
= V
DD
/ 2, T
A
= +25°C, unless otherwise noted.)
MAX7480
NORMALIZED OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX7480 toc10
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. INPUT SIGNAL AMPLITUDE
-10
-20
-30
THD+N (dB)
-40
-50
-60
-70
A
B
NO LOAD
(SEE TABLE A)
MAX7480 toc11
1.03
NORMALIZED OSCILLATOR FREQUENCY
C
OSC
= 530pF
1.02
1.01
1
0.99
0.98
0
-80
0.97
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
-90
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
AMPLITUDE (Vp-p)
Table A. THD+N vs. Input Signal
Amplitude Test Conditions
TRACE
A
B
f
IN
(Hz)
400
200
f
C
(kHz)
2
1
f
CLK
(kHz)
200
100
MEASUREMENT
BANDWIDTH (kHz)
22
22
_______________________________________________________________________________________
5
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