MAX7401ESA+T Maxim Integrated Products, MAX7401ESA+T Datasheet - Page 7

• Manufacturer Part Number: MAX7401ESA+T
• Description: IC FILTER LOWPASS 8-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of MAX7401ESA+T

• Filter Type: Bessel, Lowpass Switched Capacitor
• Frequency - Cutoff Or Center: 5kHz
• Number Of Filters: 1
• Max-order: 8th
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX7401/MAX7405 Bessel filters provide low over-
shoot and fast settling responses. Both parts operate
with a 100:1 clock-to-corner frequency ratio and a 5kHz
maximum corner frequency.
Lowpass Bessel filters such as the MAX7401/MAX7405
delay all frequency components equally, preserving the
shape of step inputs (subject to the attenuation of the
higher frequencies). Bessel filters settle quickly—an
important characteristic in applications that use a multi-
plexer (mux) to select an input signal for an analog-to-
digital converter (ADC). An anti-aliasing filter placed
between the mux and the ADC must settle quickly after
a new channel is selected.
Figure 1 shows the difference between Bessel and
Butterworth filters when a 1kHz square wave is applied
to the filter input. 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 8th-order ladder filter
structure.
_______________Detailed Description
PIN
1
2
3
4
5
6
7
8
NAME
SHDN
COM
GND
OUT
CLK
V
OS
IN
DD
_______________________________________________________________________________________
Common Input. Biased internally at mid-supply. Bypass externally to GND with a 0.1µF capacitor. To over-
ride internal biasing, drive with an external supply.
Filter Input
Ground
Positive Supply Input: +5V for MAX7401, +3V for MAX7405
Filter Output
Offset Adjust Input. To adjust output offset, bias OS externally. Connect OS to COM if no offset adjustment is
needed. Refer to
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to V
Clock Input. To override the internal oscillator, connect to an external clock; otherwise, connect an external
capacitor (C
Background Information
OSC
) from CLK to GND to set the internal oscillator frequency.
Offset and Common-Mode Input Adjustment section.
8th-Order, Lowpass, Bessel,
Switched-Capacitor Filters
Figure 1. Bessel vs. Butterworth Filter Response
Figure 2. 8th-Order Ladder Filter Network
FUNCTION
+
-
V
R1
IN
C
A
B
A: 1kHz INPUT SIGNAL
B: BESSEL FILTER RESPONSE; f
C: BUTTERWORTH FILTER RESPONSE; f
L1
C2
L3
C4
200 s/div
DD
C
Pin Description
= 5kHz
L5
for normal operation.
C6
C
= 5kHz
L7
C8
2V/div
2V/div
2V/div
R2
V
0
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