LTC6603 Linear Technology, LTC6603 Datasheet - Page 22

• Manufacturer Part Number: LTC6603
• Description: Dual Adjustable Lowpass Filter
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
LTC6603
gramming the LTC6603 for the lowest cutoff frequency
(LPF1 = ‘0’, LFP0 = ‘0’) reduces the supply current by
about 60%. Power supply current vs. cutoff frequency
for various bandwidth settings is shown in the “Typical
Performance Characteristics” section. The LTC6603 can
be programmed through the serial interface to enter into
a low power shutdown mode. The power supply current
during shutdown is less than 235μA.
Supply Current vs. Noise Tradeoff
The passband of the LTC6603 is determined by the master
clock frequency (which is set by R
oscillator is used), LPF1 and LPF0. The LTC6603 is op-
timized for use with R
and 30.9k to set the internal oscillation frequency from
12.36MHz to 80MHz. The lowpass corner frequency is
proportional to the clock frequency (internal or external).
22
Figure 14. f
100
10
10k
LPF1 = 0
LPF0 = 0
FILTER CUTOFF FREQUENCY (Hz)
CLK
100k
Table 7. Total Input Referred Integrated Noise Voltage (Passband Gain = 24dB)
BIAS
vs Filter Cutoff Frequencies
having a value between 200k
LPF1
1M
LPF1 = 0
LPF0 = 1
0
0
1
LPF1 = 1
BIAS
when the internal
6603 F14
10M
LPF0
0
1
X
To extend the fi lter’s operational frequency range, the
master clock is divided down before reaching the fi lter.
LPF1 and LPF0 set the division ratio of the lowpass clock.
Figure 14 shows the possible cutoff frequencies versus
f
more than one possible choice of bandwidth settings for
some cutoff frequencies. Figure 15 shows supply current
as a function of the fi lter cutoff frequency, LPF1 and LPF0.
Note that the higher bandwidth setting always gives the
minimum supply current for a given cutoff frequency. The
input referred integrated noise voltage for a passband
gain of 24dB is shown in Table 7. Note that the noise is
higher for the higher bandwidth settings. This creates a
tradeoff between supply current and noise. For a given
cutoff frequency, using the highest possible bandwidth
setting gives the minimum supply current at the expense
of higher noise.
CLK
, LPF1 and LPF0. Overlapping frequency ranges allow
Figure 15. Supply Current vs Filter Cutoff Frequency
180
160
140
120
100
80
60
40
20
0
10k
T
V
CLKCNTL PIN FLOATING
GAIN = 0dB
A
S
= 25°C
= 3V
LPF1 = 0
LPF0 = 0
Noise Voltage
FILTER CUTOFF FREQUENCY (Hz)
–81dBm
–80dBm
–76dBm
100k
LPF1 = 0
LPF0 = 1
1M
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LPF1 = 1
6603 F15
10M
6603f