LTC1164-5_15 Datasheet, PDF (8/16 Pages) Linear Technology – Low Power 8th Order Pin Selectable Butterworth or Bessel Lowpass Filter

LTC1164-5
PI FU CTIO S
Power Supply (Pins 4, 12)
The V⁺ (Pin 4) and the V ^– (Pin 12) should be bypassed with
a 0.1µF capacitor to an adequate analog ground. The
filter’s power supplies should be isolated from other
digital or high voltage analog supplies. A low noise linear
supply is recommended. Using a switching power supply
will lower the signal-to-noise ratio of the filter. The supply
during power-up should have a slew rate less than 1V/µs.
When V⁺ is applied before V ^–, and V ^– can be more positive
than ground, a signal diode must be used to clamp V ^–.
Figures 1 and 2 show typical connections for dual and
single supply operation.
V_IN
V⁺
0.1µF
1
14
2
13
3
12
4
11
LTC1164-5
5
10
6
9
7
8
V^–
*
0.1µF
1k
CLOCK SOURCE
GND
+
DIGITAL SUPPLY
* OPTIONAL (SEE TEXT)
V_OUT
1164-5 F01
Figure 1. Dual Supply Operation for f_CLK/f_CUTOFF = 100:1
Clock Input (Pin 11)
Any TTL or CMOS clock source with a square-wave output
and 50% duty cycle (±10%) is an adequate clock source
for the device. The power supply for the clock source
should not be the filter’s power supply. The analog ground
for the filter should be connected to clock’s ground at a
single point only. Table 1 shows the clock’s low and high
level threshold value for a dual or single supply operation.
A pulse generator can be used as a clock source provided
the high level ON time is greater than 0.5µs. Sine waves are
not recommended for clock input frequencies less than
100kHz, since excessively slow clock rise or fall times
generate internal clock jitter (maximum clock rise or fall
time ≤1µs). The clock signal should be routed from the
right side of the IC package to avoid coupling into any input
or output analog signal path. A 1k resistor between clock
source and Pin 11 will slow down the rise and fall times of
the clock to further reduce charge coupling, Figures 1
and 2.
Table 1. Clock Source High and Low Threshold Levels
POWER SUPPLY
Dual Supply > ±3.4V
Dual Supply ≤ ±3.4V
Single Supply V⁺ > 6.8V, V ^– = 0V
Single Supply V⁺ < 6.8V, V ^– = 0V
HIGH LEVEL
≥ V ⁺/3
≥ V ⁺/3
≥ V ⁺• 0.65
≥ V ⁺/3
LOW LEVEL
≤ 0.5V
≤ V ^– + 0.5V
≤ 0.5V + 1/2V ⁺
≤ 0.5V
V_IN
5V ≤ V⁺ ≤16V
10k
10k
1
14
2
13
0.1µF
3
12
4 _LTC1164-5 11
1k
5
10
CLOCK SOURCE
6
9
7
8
GND
+
DIGITAL SUPPLY
+
1µF
V_OUT
1164-5 F02
Figure 2. Single Supply Operation for f_CLK/f_CUTOFF = 100:1
Analog Ground (Pins 3, 5)
The filter performance depends on the quality of the
analog signal ground. For either dual or single supply
operation, an analog ground plane surrounding the pack-
age is recommended. The analog ground plane should be
connected to any digital ground at a single point. For dual
supply operation, Pins 3 and 5 should be connected to the
analog ground plane. For single supply operation Pins 3
and 5 should be biased at 1/2 supply and they should be
bypassed to the analog ground plane with at least a 1µF
capacitor (Figure 2). For single 5V operation at the highest
f_CLK of 1MHz, Pins 3 and 5 should be biased at 2V. This
minimizes passband gain and phase variations (see Typi-
cal Performance Characteristics curves: Maximum Pass-
band for Single 5V, 50:1; and THD + Noise vs RMS Input
for Single 5V, 50:1).
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