TL H 10557
LMF40
High
Performance
4th-Order
Switched-Capacitor
Butterworth
Low-Pass
Filter
December 1994
LMF40 High Performance 4th-Order
Switched-Capacitor Butterworth Low-Pass Filter
General Description
The LMF40 is a versatile easy to use precision 4th-order
Butterworth low-pass filter fabricated using National's high
performance LMCMOS process Switched-capacitor tech-
niques eliminate external component requirements and al-
low a clock-tunable cutoff frequency The ratio of the clock
frequency to the low-pass cutoff frequency is internally set
to 50-to-1 (LMF40-50) or 100-to-1 (LMF40-100) A Schmitt
trigger clock input stage allows two clocking options either
self-clocking (via an external resistor and capacitor) for
stand-alone applications or for tighter cutoff frequency con-
trol an external TTL or CMOS logic compatible clock can
be applied The maximally flat passband frequency re-
sponse together with a DC gain of 1 V V allows cascading
LMF40 sections together for higher-order filtering
Features
Y
Cutoff frequency range of 0 1 Hz to 40 kHz
Y
Cutoff frequency accuracy of
g
1 0% maximum
Y
Low offset voltage
g
100 mV maximum
g
5V supply
Y
Low clock feedthrough of 5 mV
P-P
typical
Y
Dynamic range of 88 dB typical
Y
No external components required
Y
8-pin mini-DIP or 14-pin wide-body small-outline pack-
ages
Y
4V to 14V single dual supply operation
Y
Cutoff frequency set by external or internal clock
Y
Pin-compatible with MF4
Applications
Y
Communication systems
Y
Instrumentation
Y
Automated control systems
Block and Connection Diagrams
TL H 10557 1
Pin numbers in parentheses are for the 14-pin package
Ordering Information
Industrial (
b
40 C
s
T
A
s
a
85 C)
Package
LMF40CIN-50 LMF40CIN-100
N08E
LMF40CIWM-50
M14B
LMF40CIWM-100
M14B
Military (
b
55 C
s
T
A
s
a
125 C)
LMF40CMJ-50 LMF40CMJ-100
J08A
Dual-In-Line Package
TL H 10557 2
Top View
Small-Outline-Wide-Body Package
TL H 10557 3
Top View
TRI-STATE
is a registered trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation
RRD-B30M115 Printed in U S A
Absolute Maximum Ratings
(Notes 1
2)
If Military Aerospace specified devices are required
please contact the National Semiconductor Sales
Office Distributors for availability and specifications
Supply Voltage (V
a
V
b
)
15V
Voltage at Any Pin
V
b
b
0 2V to V
a
a
0 2V
Input Current at Any Pin (Note 13)
5 mA
Package Input Current (Note 13)
20 mA
Power Dissipation (Note 14)
500 mW
Storage Temperature
b
65 C to
a
150 C
Lead Temperature
N Package Soldering (10 sec )
a
260 C
J Package Soldering (10 sec )
a
300 C
WM Package Vapor Phase (60 sec ) (Note 16)
a
215 C
WM Package Infrared (15 sec )
a
220 C
ESD Susceptibility (Note 12)
2000V
Pin 1 CLK IN
1700V
Operating Ratings
(Notes 1
2)
Temperature Range
T
MIN
s
T
A
s
T
MAX
LMF40CIN-50 LMF40CIN-100
LMF40CIWM-50
LMF40CIWM-100
b
40 C
s
T
A
s
a
85 C
LMF40CMJ-50 LMF40CMJ-100
b
55 C
s
T
A
s
a
125 C
Supply Voltage Range (V
a
b
V
b
)
4V to 14V
Filter Electrical Characteristics
The following specifications apply for f
CLK
e
500 kHz Boldface limits apply for T
A
e
T
J
e
T
MIN
to T
MAX
All other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
V
a
e a
5V V
b
e b
5V
f
CLK
Clock Frequency Range
(Note 17)
5
Hz (min)
2
MHz (max)
I
S
Supply Current
CMJ
3 5
7 0
mA (max)
CIN CIJ CIWM
3 5
5 0
mA (max)
H
O
DC Gain
R
Source
s
2 kX
a
0 05
a
0 05
dB (max)
b
0 15
b
0 20
dB (min)
f
CLK
f
c
Clock to Cutoff
Frequency Ratio
(Note 3)
LMF40-50
49 80
g
0 8%
49 80
g
1 0%
(max)
LMF40-100
99 00
g
0 8%
99 00
g
1 0%
(max)
D
f
CLK
f
c
D
T
Clock to Cutoff Frequency
Ratio Temperature
Coefficient
LMF40-50
5
ppm C
LMF40-100
5
ppm C
A
MIN
Stopband Attenuation
At 2 f
c
24 0
dB (min)
2
Filter Electrical Characteristics
(Continued)
The following specifications apply for f
CLK
e
500 kHz Boldface limits apply for T
A
e
T
J
e
T
MIN
to T
MAX
All other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
V
a
e a
5V V
b
e b
5V
(Continued)
V
OS
Unadjusted DC
Offset Voltage
LMF40-50
g
80
g
100
mV (max)
LMF40-100
g
80
g
100
mV (max)
V
O
Output Swing
R
L
e
5 kX
a
3 9
a
3 7
V (min)
b
4 2
b
4 0
V (max)
I
SC
Output Short Circuit
Source
90
mA
Current (Note 8)
Sink
2 2
mA
Dynamic Range
88
dB
(Note 4)
Additional Magnitude
Response Test Points
(Note 6)
LMF40-50
f
IN
e
12 kHz
b
7 50
g
0 26
b
7 50
g
0 30
dB (max)
f
IN
e
9 kHz
b
1 46
g
0 12
b
1 46
g
0 16
dB (max)
LMF40-100
f
IN
e
6 kHz
b
7 15
g
0 26
b
7 15
g
0 30
dB (max)
f
IN
e
4 5 kHz
b
1 42
g
0 12
b
1 42
g
0 16
dB (max)
Clock Feedthrough
Filter Output
5
mV
P P
V
IN
e
0V
Filter Electrical Characteristics
The following specifications apply for f
CLK
e
250 kHz Boldface limits
apply for T
A
e
T
J
e
T
MIN
to T
MAX
All other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
V
a
e a
2 5V V
b
e b
2 5V
f
CLK
Clock Frequency Range
(Note 17)
5
Hz (min)
1 0
MHz (max)
I
S
Supply Current
CMJ
2 1
4 0
mA (max)
CIN CIJ CIWM
2 1
3 0
mA (max)
H
O
DC Gain
R
S
s
2 kX
a
0 05
a
0 05
dB (max)
f
CLK
e
250 kHz
b
0 15
b
0 20
dB (min)
f
CLK
e
500 kHz
b
0 1
dB
f
CLK
f
c
Clock to Cutoff
Frequency Ratio
LMF40-50
f
CLK
e
250 kHz
49 80
g
0 8%
(max)
f
CLK
e
500 kHz
49 80
g
0 6%
LMF40-100
f
CLK
e
250 kHz
99 00
g
1 0%
99 00
g
1 2%
(max)
(Note 3)
f
CLK
e
500 kHz
99 00
g
1 2%
3
Filter Electrical Characteristics
(Continued)
The following specifications apply for f
CLK
e
250 kHz Boldface limits apply for T
A
e
T
J
e
T
MIN
to T
MAX
All other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
V
a
e a
2 5V V
b
e b
2 5V
(Continued)
D
f
CLK
f
c
D
T
Clock to Cutoff
Frequency Ratio
Temperature Coefficient
LMF40-50
5
ppm C
LMF40-100
5
ppm C
A
MIN
Stopband Attenuation
At 2 f
c
b
24 0
dB (min)
V
OS
Unadjusted DC
Offset Voltage
LMF40-50
g
80
g
100
mV (max)
LMF40-100
g
80
g
100
mV (max)
V
O
Output Swing
R
L
e
5 kX
a
1 4
a
1 2
V (min)
b
2 0
b
1 8
V (max)
I
SC
Output Short Circuit
Source
42
mA
Current (Note 8)
Sink
0 9
mA
Dynamic Range
81
dB
(Note 4)
Additional Magnitude Response
Test Points (Note 6)
LMF40-50
f
IN
e
6 kHz
b
7 50
g
0 26
b
7 50
g
0 30
dB (max)
f
IN
e
4 5 kHz
b
1 46
g
0 12
b
1 46
g
0 16
dB (max)
LMF40-100
f
IN
e
3 kHz
b
7 15
g
0 26
b
7 15
g
0 30
dB (max)
f
IN
e
2 25 kHz
b
1 42
g
0 12
b
1 42
g
0 16
dB (max)
Clock Feedthrough
Filter Output
5
mV
P P
V
IN
e
0V
Logic Input-Output Characteristics
The following specifications apply for V
b
e
0V unless otherwise
specified Boldface limits apply for T
A
e
T
J
e
T
MIN
to T
MAX
all other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
TTL CLOCK INPUT CLK R PIN
(Note 9)
TTL CLK R Pin Input Voltage
V
a
e a
5V
V
b
e b
5V
Logic ``1''
2 0
2 1
V (min)
Logic ``0''
0 8
0 8
V (max)
CLK R Input Voltage
V
a
e a
2 5V
V
b
e b
2 5V
Logic ``1''
2 0
2 0
V (min)
Logic ``0''
0 6
0 4
V (max)
Maximum Leakage Current
2 0
m
A
at CLK R Pin
SCHMITT TRIGGER
V
T
a
Positive Going Input
V
a
e a
10V
6 1
6 0
V (min)
Threshold Voltage
8 8
8 9
V (max)
CLK IN Pin
V
a
e a
5V
3 0
2 9
V (min)
4 3
4 4
V (max)
4
Logic Input-Output Characteristics
(Continued) The following specifications apply for V
b
e
0V unless
otherwise specified Boldface limits apply for T
A
e
T
J
e
T
MIN
to T
MAX
all other limits T
A
e
T
J
e
25 C
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 10)
(Note 11)
(Limit)
SCHMITT TRIGGER
(Continued)
V
T
b
Negative Going Input
V
a
e a
10V
1 4
1 3
V (min)
Threshold Voltage
3 8
3 9
V (max)
CLK IN Pin
V
a
e a
5V
0 7
0 6
V (min)
1 9
2 0
V (max)
V
T
a b
V
T
b
Hysteresis CLK IN Pin
V
a
e a
10V
2 3
2 1
V (min)
7 4
7 6
V (max)
V
a
e a
5V
1 1
0 9
V (min)
3 6
3 8
V (max)
Logical ``1'' Output
I
O
e b
10 mA
Voltage CLK R
V
a
e a
10V
9 1
9 0
V (min)
Pin
V
a
e a
5V
4 6
4 5
V (min)
Logical ``0'' Output
I
O
e b
10 mA
Voltage CLK R
V
a
e a
10V
0 9
1 0
V (max)
Pin
V
a
e a
5V
0 4
0 5
V (max)
Output Source Current
CLK R to V
b
CLK R Pin
V
a
e a
10V
4 9
3 7
mA (min)
V
a
e a
5V
1 6
1 2
mA (min)
Output Sink Current
CLK R to V
a
CLK R Pin
V
a
e a
10V
4 9
3 7
mA (min)
V
a
e a
5V
1 6
1 2
mA (min)
Note 1
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur DC and AC electrical specifications do not apply when operating
the device beyond its specified operating range
Note 2
All voltages are specified with respect to ground
Note 3
The filter's cutoff frequency is defined as the frequency where the magnitude response is 3 01 dB less than the DC gain of the filter
Note 4
For
g
5V supplies the dynamic range is referenced to 2 62 V
rms
(3 7V peak) where the wideband noise over a 20 kHz bandwidth is typically 100 mV
rms
for
the LMF40 For
g
2 5V supplies the dynamic range is referenced to 0 849 V
rms
(1 2V peak) where the wideband noise over a 20 kHz bandwidth is typically
75 mV
rms
for the LMF40
Note 5
The specifications for the LMF40 have been given for a clock frequency (f
CLK
) of 500 kHz at
g
5V and 250 kHz at
g
2 5V Above this clock frequency the
cutoff frequency begins to deviate from the specified error band of
g
0 8% over the temperature range but the filter still maintains its magnitude characteristics
See Application Information Section 1 4
Note 6
The filter's magnitude response is tested at the cutoff frequency f
c
f
S
e
2 f
c
and at these other two additional frequencies
Note 7
For simplicity all logic levels have been referenced to V
b
e
0V (except for the TTL input logic levels) The logic levels will scale accordingly for
g
5V and
g
2 5V supplies
Note 8
The short circuit source current is measured by forcing the output that is being tested to its maximum positive swing and then shorting that output to the
negative supply The short circuit sink current is measured by forcing the output that is being tested to its maximum negative voltage and then shorting that output
to the positive supply These are worst case conditions
Note 9
The LMF40 is operated with symmetrical supplies and L Sh is tied to ground
Note 10
Typicals are at T
J
e
25 C and represent the most likely parametric norm
Note 11
Guaranteed to National's AOQL (Average Outgoing Quality Level)
Note 12
Human body model 100 pF discharged through a 1 5 kX resistor
Note 13
When the input voltage (V
IN
) at any pin exceeds the power supply voltages (V
IN
k
V
b
or V
IN
l
V
a
) the absolute value of the current at that pin should
be limited to 5 mA or less The 20 mA package input current limits the number of pins that can exceed the power supply voltages with 5 mA current limit to four
Note 14
The maximum power dissipation must be de-rated at elevated temperatures and is dictated by T
JMAX
i
JA
and the ambient temperature T
A
The
maximum allowable power dissipation is PD
e
(T
JMAX
b
T
A
) i
JA
or the number given in the Absolute Maximum Ratings whichever is lower For the LMF40
T
JMAX
e
125 C and the typical junction-to-ambient thermal resistance when board mounted is 67 C W for the LMF40CIN 62 C W for the LMF40CIJ and
LMF40CMJ and 78 C W for the LMC40CIWM
Note 15
In popular usage the term cutoff frequency defines that frequency at which a filter's gain drops 3 01 dB below its DC value Equations (2) and (3) and
design example 2 1 however use the term cutoff frequency (f
b
) to define that frequency at which a filter's gain drops by a variable amount as determined from the
given design specifications
Note 16
See AN-450 ``Surface Mounting Methods and Their Effect on Product Reliability'' for other methods of soldering surface mount devices or see the section
titled ``Surface Mount'' in the
Linear Data Book
Note 17
The nominal ratio of the clock frequency to the low-pass cutoff frequency is internally set to 50-to-1 (LMF40-50) or 100-to-1 (LMF40-100)
5
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