LTC1569CS8-7 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC1569CS8-7 Datasheet PDF : 12 Pages
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LTC1569-7
APPLICATIONS INFORMATION
Self-Clocking Operation
The LTC1569-7 features a unique internal oscillator which
sets the filter cutoff frequency using a single external
resistor. The design is optimized for VS = 3V, fCUTOFF =
128kHz, where the filter cutoff frequency error is typically
<1% when a 0.1% external 10k resistor is used. With
different resistor values and internal divider settings, the
cutoff frequency can be accurately varied from 2kHz to
150kHz/300kHz (single 3V/5V supply). As shown in
Figure 1, the divider is controlled by the DIV/CLK (Pin 5).
Table 1 summarizes the cutoff frequency vs external
resistor values for the divide-by-1 mode.
In the divide-by-4 and divide-by-16 modes, the cutoff
frequencies in Table 1 will be lowered by 4 and 16
respectively. When the LTC1569-7 is in the divide-by-4
and divide-by-16 modes the power is automatically
1 IN+
OUT 8
2 IN–
V+ 7
LTC1569-7
3 GND
RX 6
4 V– DIV/CLK 5
fCUTOFF = 128kHz (10k/REXT)
1, 4 OR 16
REXT
DIVIDE-BY-16
V+
DIVIDE-BY-4
100pF
V–
DIVIDE-BY-1
1569-7 F01
Figure 1
1.010
1.008
1.006
1.004
VS = 3V
VS = 5V
VS = 10V
1.002
1.000
0.998
0.996
0.994
0.992
0.990
–50 –25 0
25 50 75 100
TEMPERATURE (°C)
1569-7 F03
Figure 3. Filter Cutoff vs Temperature,
Divide-by-1 Mode, REXT = 10k
reduced. This results in a 60% power savings with a single
5V supply.
Table1. fCUTOFF vs REXT, VS = 3V, TA = 25°C, Divide-by-1 Mode
REXT
Typical fCUTOFF
Typical Variation of fCUTOFF
3844Ω
320kHz
±3.0%
5010Ω
256kHz
±2.5%
10k
128kHz
±1%
20.18k
64kHz
±2.0%
40.2k
32kHz
±3.5%
The power reduction in the divide-by-4 and divide-by-16
modes, however, effects the fundamental oscillator fre-
quency. Hence, the effective divide ratio will be slightly
different from 4:1 or 16:1 depending on VS, TA and REXT.
Typically this error is less than 1% (Figures 4 and 6).
1.04
1.03
REXT = 5k
REXT = 10k
1.02
REXT = 20k
REXT = 40k
1.01
1.00
0.99
0.98
0.97
0.96
2
4
6
8
10
VSUPPLY (V)
1569-7 F02
Figure 2. Filter Cutoff vs VSUPPLY,
Divide-by-1 Mode, TA = 25°C
4.08
REXT = 5k
REXT = 10k
REXT = 20k
REXT = 40k
4.04
4.00
3.96
2
4
6
8
10
VSUPPLY (V)
1569-7 F04
Figure 4. Typical Divide Ratio in the
Divide-by-4 Mode, TA = 25°C
6
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