MAX7408EUA+ Maxim Integrated Products, MAX7408EUA+ Datasheet - Page 9

• Manufacturer Part Number: MAX7408EUA+
• Description: IC FILTER LOWPASS 5TH 8UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX7408EUA+

• Filter Type: Elliptic, 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

Figure 2. Elliptic Filter Response
These SCFs are designed for use with external clocks
that have a 40% to 60% duty cycle. When using an
external clock, drive the CLK pin with a CMOS gate
powered from 0 to V
clock adjusts the corner frequency of the filter:
When using the internal oscillator, the capacitance
(C
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 100kHz produces a
nominal corner frequency of 1kHz.
The MAX7408/MAX7411/MAX7412/MAX7415’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 by the equation 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
PASSBAND
is in the low picofarads, minimize the stray
f OSC (kHz)
_______________________________________________________________________________________
f
C
DD
f
C
f
C
. Varying the rate of the external
=
TRANSITION RATIO =
f
S
=
f
100
CLK
RIPPLE
f
C OSC (pF)
S
k
STOPBAND
FREQUENCY
Clock Signal
f
f
C
External Clock
S
Internal Clock
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
Estimate the input impedance of the filter by using the
following formula:
where f
The MAX7408/MAX7411/MAX7412/MAX7415 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 imped-
ance. For normal operation, drive SHDN high or con-
nect to V
COM sets the common-mode input voltage and is
biased at mid-supply with an internal resistor-divider. If
the application does not require offset adjustment, con-
nect OS to COM. For applications where offset adjust-
ment is required, apply an external bias voltage
through a resistor-divider network to OS, as shown in
Figure 3. 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 3. Offset Adjustment Circuit
0.1µF
CLOCK
INPUT
CLK
Offset (OS) and Common-Mode (COM)
V
SUPPLY
DD
IN
= 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
=
=
MAX7408
MAX7411
MAX7412
MAX7415
(
V
V
V
GND
(f
IN
DD
DD
2
CLK
−
(
typical
1
×
V
SHDN
COM
COM
OUT
C )
OS
Input Adjustment
IN
0.1µF
0.1µF
)
)
IN
+
= 1pF.
V
OUTPUT
OS
50k
50k
50k
9