MAX7421CUA Maxim Integrated Products, MAX7421CUA Datasheet - Page 11

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MAX7421CUA

Manufacturer Part Number
MAX7421CUA
Description
Active Filter
Manufacturer
Maxim Integrated Products
Datasheet

Specifications of MAX7421CUA

Number Of Channels
1
Cutoff Frequency
30 KHz
Supply Voltage (max)
5.5 V
Maximum Operating Temperature
+ 70 C
Minimum Operating Temperature
0 C
Mounting Style
SMD/SMT
Operating Supply Voltage
5 V
Supply Voltage (min)
4.5 V
Package / Case
uMAX-8
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
MAX7421CUA
Manufacturer:
MAXIM/美信
Quantity:
20 000
Figure 3. Bessel vs. Butterworth Filter Response
When using the internal oscillator, the capacitance
(C
where
k=87x10
MAX7418/MAX7421/MAX7422/MAX7425
and
k=110X10
MAX7419/MAX7420/MAX7423/ MAX7424.
Since C
capacitance at CLK so that it does not affect the inter-
nal oscillator frequency. Varying the rate of the internal
oscillator adjusts the filter’s corner frequency by a
100:1 clock-to-corner frequency ratio. For example, an
internal oscillator frequency of 2.2kHz produces a nom-
inal corner frequency of 2.2MHz.
The MAX7418–MAX7425s’ input impedance is effective-
ly that of a switched-capacitor resistor (see the following
equation), and is inversely proportional to frequency.
The input impedance values determined by the equa-
tion represent the average input impedance, since the
input current is not continuous. As a rule, use a driver
with an output resistance less than 10% of the filter’s
input impedance.
OSC
Input Impedance vs. Clock Frequencies
) on CLK determines the oscillator frequency:
OSC
3
for the
3
A
B
C
A: 1kHz INPUT SIGNAL
B: MAX7419 BESSEL FILTER RESPONSE; f
C: MAX7420 BUTTERWORTH FILTER RESPONSE; f
for the
is in the low picofarads, minimize the stray
f OSC (kHz)
______________________________________________________________________________________
200μs/div
=
C OSC (pF)
k
C
= 5kHz
C
Internal Clock
= 5kHz
2V/div
2V/div
2V/div
Switched-Capacitor Filters
Estimate the input impedance of the filter by using the
following formula:
where f
The MAX7418–MAX7425 have a shutdown mode that is
activated by driving SHDN low. In shutdown mode, the
filter supply current reduces to 0.2µA, and the output of
the filter becomes high impedance. For normal opera-
tion, drive SHDN high or connect to V
COM sets the common-mode input voltage and is
biased at midsupply with an internal resistor-divider. If
the application does not require offset adjustment, con-
nect OS to COM. For applications in which offset
adjustment is required, apply an external bias voltage
through a resistor-divider network to OS, as shown in
Figure 4. For applications that require DC level shifting,
adjust OS with respect to COM. (Note: Do not leave OS
unconnected.) The output voltage is represented by
these equations:
where (V
OS is added at the output stage. See the Electrical
Figure 4. Offset Adjustment Circuit
0.1μF
CLOCK
INPUT
5th-Order, Lowpass,
Offset (OS) and Common-Mode (COM)
CLK
V
IN
SUPPLY
= clock frequency and C
- V
V
V
OUT
COM
COM
IN
CLK
Applications Information
Z
IN
) is lowpass filtered by the SCF and
Low-Power Shutdown Mode
=
=
MAX7418–
MAX7425
=
(
V
V
GND
V
IN
DD
DD
(f
2
CLK
(
typical
SHDN
V
COM
OUT
1
×
COM
OS
Input Adjustment
C )
0.1μF
0.1μF
IN
)
)
IN
DD
+
OUTPUT
= 1pF.
V
.
OS
50k
50k
50k
11

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