MAX261BCNG Maxim Integrated Products, MAX261BCNG Datasheet - Page 20

• Manufacturer Part Number: MAX261BCNG
• Description: Active Filter Integrated Circuits (ICs)
• Manufacturer: Maxim Integrated Products

Specifications of MAX261BCNG

• Number Of Channels: 2
• Cutoff Frequency: 57 KHz
• Supply Voltage (max): 12.6 V
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Operating Supply Voltage: 5 V
• Supply Voltage (min): 4.74 V
• Package / Case: PDIP N
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

can also perform this last step. The desired f
are stated, and the appropriate digital coefficients are
supplied.
In some designs, such as very narrow band filters, sev-
eral second-order sections with identical center fre-
quency can be cascaded. The total Q of the resultant
filter is:
Q is the Q of each individual filter section, and N is the
number of sections. In Table 6, the total Q and band-
width are listed for up to five identical second-order
sections. B is the bandwidth of each section.
In high-order bandpass filters, stages with different f
and Qs are also often cascaded. When this happens,
the overall filter gain at the bandpass center frequency
is not simply the product of the individual gains
because f
specified, is different for each second-order section.
The gain of each section at the cascaded filter's center
frequency must be determined to obtain the total gain.
For all-pole filters the gain, H(f
section's f
obtain that section's gain, H(f
frequency:
H
where F
G
f
The gain of the other sections (2, 3, etc.) at f
determined the same way. The overall gain is:
H(f
For cascaded filters with zeros (f
gain adjustment factor for each stage is:
where F
Microprocessor Programmable
Universal Active Filters
20
Total Q
0
G
G
1
1
1
(f
for the first of the cascaded second-order sections.
, Q
1
0Bp
0BP
=
______________________________________________________________________________________
=
1
) = H
, and f
Q F
) = H(f
1
1Z
T
Q
1
= f
1
0

 
0
=
= f

 
, the frequency where each sections gain is
1
(
Z
01
F
is divided by an adjustment factor, G, to
(f
1
1
z1
01
2
01
2
0BP
(
/ f
−
2
−
/ f
) / G
are the gain adjustment factor, Q, and
1
OBP
) x H
/
0BP
1
F
Q
N
1
)
2
2
1

 
−
F
+
, and F
F

 
= Section 1’s Gain at f
2
1
1
(
2
1
(f
F
(
F


)
1
0BP
1
2
F
Z
−
/
1
) x etc.
2
1
Q
1
0BP
−
)
is the same as above.
0
1
2
)
), as each second-order
2 1 2
1
Z
+
Cascading Filters
), at the overall center

 


) such as elliptics, the
/
(
F
1
/
Q
1
)
2 1 2
0BP

 
0
/
s and Qs
0BP
0
is
s
The MAX260/MAX261/MAX262 can be operated with a
variety of power supply configurations, including +5V to
+12V single supply or ±2.5V to ±5V dual supplies.
When a single supply is used, V
tem ground and the filter's GND pin should be biased
at V
pled to the filter input or biased to V
shows circuit connections for single-supply operation.
When power supplies other than ±5V are used, CMOS
input logic levels (HIGH = V
required for WR, D0, D1, A0–A3, OLK
With ±5V supplies, either TTL or CMOS levels can be
used. Note, however, that power consumption at ±5V is
reduced if CLK
than TTL or 0 to 5V levels. Operation with +5V or ±2.5V
power lowers power consumption, but also reduces
bandwidth by approximately 25% compared to +12V or
±5V supplies.
Best performance is achieved if V
to ground with 4.7µF electrolytic (Tantalum is preferred.)
and 0.1µF ceramic capacitors. These should be located
as close to the supply pins as possible. The lead length
of the bypass capacitors should be shortest at the V
and V
should be bypassed to V
MAX260/MAX261/MAX262 outputs are designed to
drive 10kΩ loads. For the MAX261 and MAX262, all fil-
ter outputs swing to within 0.15V of each supply rail
with a 10kΩ load. In the MAX260 only, an internal sam-
ple-hold circuit reduces voltage swing at the N/HP/AP
output compared to LP and BR. N/HP/AP, therefore,
swings to within 1V (10kΩ load) of either rail on the
MAX260.
To ensure that the outputs are not driven beyond their
maximum range (output clipping), the peak amplitude
response, individual section gains (H
H
be carefully considered. It is especially important to
check unused outputs for clipping (i.e., the lowpass
output in a bandpass hookup), because overload at
any filter stage severely distorts the overall response.
The maximum signal swing with ±4.75V supplies and a
1.0V filter offset is approximately ±3.5V.
For example, lets assume a fourth-order lowpass filter is
being implemented with a Q of 2 using mode 1. With a
single 5V supply (i.e., ±2.5V with respect to chip GND)
the maximum output signal is ±2V (w.r.t. GND). Since in
OHP
+
/2. The input signal is then either capacitively cou-
), input signal level, and filter offset voltages must
-
pins. When using a single supply, V
A
and CLK
Output Swing and Clipping
-
as shown in Figure 16.
B
Application Hints
are driven with ±5V, rather
+
, LOW = GND or V
+
-
is connected to sys-
and V
Power Supplies
+
-
A
/2. Figure 16
are bypassed
, and CLK
OBP
+
and GND
, H
-
) are
OLP
B
+
.
,