MAX7410EUA+ Maxim Integrated Products, MAX7410EUA+ Datasheet - Page 8

IC FILTER LOWPASS 5TH 8UMAX

MAX7410EUA+

Manufacturer Part Number
MAX7410EUA+
Description
IC FILTER LOWPASS 5TH 8UMAX
Manufacturer
Maxim Integrated Products
Datasheet

Specifications of MAX7410EUA+

Filter Type
Butterworth, Lowpass Switched Capacitor
Frequency - Cutoff Or Center
15kHz
Number Of Filters
1
Max-order
5th
Voltage - Supply
4.5 V ~ 5.5 V
Mounting Type
Surface Mount
Package / Case
8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
Number Of Channels
Single
Cutoff Frequency
15 KHz
Supply Voltage (max)
5 V
Maximum Operating Temperature
+ 85 C
Minimum Operating Temperature
- 40 C
Mounting Style
SMD/SMT
Operating Supply Voltage
5 V
Supply Voltage (min)
4.5 V
For Use With
MAXFILTERBRD+ - BOARD EVAL MAX7408/7415/418-7425
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
5th-Order, Lowpass,
Switched-Capacitor Filters
The difference between Bessel and Butterworth filters
can be observed when a 1kHz square wave is applied
to the filter input (Figure 1, trace A). With the filter cutoff
frequencies set at 5kHz, trace B shows the Bessel filter
response and trace C shows the Butterworth filter
response.
Most switched-capacitor filters (SCFs) are designed with
biquadratic sections. Each section implements two filter-
ing poles, and the sections are cascaded to produce
higher-order filters. The advantage to this approach is
ease of design. However, this type of design is highly
sensitive to component variations if any section’s Q is
high. An alternative approach is to emulate a passive net-
work using switched-capacitor integrators with summing
and scaling. Figure 2 shows a basic 5th-order ladder filter
structure.
A switched-capacitor filter such as the MAX7409/
MAX7410/MAX7413/MAX7414 emulates a passive ladder
filter. The filter’s component sensitivity is low when com-
pared to a cascaded biquad design, because each
component affects the entire filter shape, not just one
pole-zero pair. In other words, a mismatched component
in a biquad design will have a concentrated error on its
respective poles, while the same mismatch in a ladder
filter design results in an error distributed over all poles.
8
Figure 1. Bessel vs. Butterworth Filter Response
_______________________________________________________________________________________
C
A
B
A: 1kHz INPUT SIGNAL
B: MAX7409 BESSEL FILTER RESPONSE; f
C: MAX7410 BUTTERWORTH FILTER RESPONSE; f
Background Information
200 s/div
C
= 5kHz
C
= 5kHz
2V/div
2V/div
2V/div
The MAX7409/MAX7410/MAX7413/MAX7414 family of
SCFs is designed for use with external clocks that have
a 50% ±10% duty cycle. When using an external clock
with these devices, drive CLK with a CMOS gate pow-
ered from 0 to V
clock adjusts the corner frequency of the filter as fol-
lows:
When using the internal oscillator, connect a capacitor
(C
capacitor determines the oscillator frequency as follows:
Minimize the stray capacitance at CLK so that it does
not affect the internal oscillator frequency. Vary the rate
of the internal oscillator to adjust the filter’s corner fre-
quency by a 100:1 clock-to-corner frequency ratio. For
example, an internal oscillator frequency of 100kHz
produces a nominal corner frequency of 1kHz.
The MAX7409/MAX7410/MAX7413/MAX7414’s input
impedance is effectively that of a switched-capacitor
resistor (see the following equation), and is inversely
proportional to frequency. The input impedance values
determined below represent the average input imped-
ance, since the input current is not continuous. As a
rule, use a driver with an output impedance less than
10% of the filter’s input impedance. Estimate the input
impedance of the filter using the following formula:
For example, an f
impedance of 4.8MΩ.
Figure 2. 5th-Order Ladder Filter Network
OSC
Input Impedance vs. Clock Frequencies
) between CLK and ground. The value of the
+
-
V
f
R
IN
OSC
S
Z
(kHz) = 30 x 10
IN
DD
C1
CLK
= 1 / ( f
f
. Varying the rate of the external
C
L2
= f
of 100kHz results in an input
C3
CLK
CLK
/ 100
x 2.1pF)
3
/ C
L4
OSC
C5
Clock Signal
External Clock
(pF)
Internal Clock
R
L

Related parts for MAX7410EUA+