1569I6 [Linear]
Linear Phase, DC Accurate, Low Power, 10th Order Lowpass Filter; 线性相位，直流精度，低功耗， 10阶低通滤波器
| 型号： | 1569I6 |
| 厂家： | 
Linear |
| 描述： | Linear Phase, DC Accurate, Low Power, 10th Order Lowpass Filter |
| 文件： | 总12页 (文件大小：192K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1569-6
Linear Phase, DC Accurate,
Low Power, 10th Order Lowpass Filter
tems. Furthermore, its root raised cosine response offers
the optimum pulse shaping for PAM data communica-
tions. The filter attenuation is 50dB at 1.5 • fCUTOFF, 60dB
at 2 • fCUTOFF, and in excess of 80dB at 6 • fCUTOFF. DC-
accuracy-sensitive applications benefit from the 5mV
maximum DC offset.
FEATURES
■
One External R Sets Cutoff Frequency
■
Root Raised Cosine Response
■
3mA Supply Current with a Single 3V Supply
■
Up to 64kHz Cutoff on a Single 3V Supply
■
10th Order, Linear Phase Filter in an SO-8
The LTC1569-6 sampled data filter does not require an
external clock yet its cutoff frequency can be set with a
single external resistor with a typical accuracy of 3.5% or
better. The external resistor programs an internal oscilla-
tor whose frequency is divided by either 1, 4 or 16 prior to
being applied to the filter network. Pin 5 determines the
divider setting. Thus, up to three cutoff frequencies can be
obtained for each external resistor value. Using various
resistor values and divider settings, the cutoff frequency
can be programmed over a range of six octaves. Alterna-
tively, the cutoff frequency can be set with an external
clock and the clock-to-cutoff frequency ratio is 64:1. The
ratio of the internal sampling rate to the filter cutoff
frequency is 128:1.
■
DC Accurate, VOS(MAX) = 5mV
■
Low Power Modes
■
Differential or Single-Ended Inputs
■
80dB CMRR (DC)
■
82dB Signal-to-Noise Ratio, VS = 5V
■
Operates from 3V to ±5V Supplies
U
APPLICATIO S
■
Data Communication Filters for 3V Operation
Linear Phase and Phase Matched Filters for I/Q
Signal Processing
Pin Programmable U Cutoff Frequency Lowpass Filters
■
■
DESCRIPTIO
The LTC1569-6 is fully tested for a cutoff frequency of
64kHz with a single 3V supply.
The LTC®1569-6 is a 10th order lowpass filter featuring
linear phase and a root raised cosine amplitude response.
The high selectivity of the LTC1569-6 combined with its
linear phase in the passband makes it suitable for filtering
both in data communications and data acquisition sys-
The LTC1569-6 features power saving modes and it is
available in an SO-8 surface mount package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Frequency Response, fCUTOFF = 64kHz/16kHz/4kHz
0
Single 3V Supply, 64kHz/16kHz/4kHz Lowpass Filter
–20
–40
1
2
8
7
+
–
V
IN
IN
OUT
V
OUT
IN
R
EXT
= 10k
1/4
3V
+
3V
1µF
V
LTC1569-6
GND
3.48k
2k
3
4
6
5
R
X
–60
3V
1µF
1/16
1/1
–
V
DIV/CLK
–80
100pF
EASY TO SET f
:
CUTOFF
–100
64kHz (10k/R
)
EXT
1
10
100
1000
f
=
CUTOFF
1569-6 TA01
1, 4 OR 16
FREQUENCY (kHz)
1569-6 TA01a
1
LTC1569-6
W
U
W W W
U
/O
ABSOLUTE AXI U RATI GS
PACKAGE RDER I FOR ATIO
(Note 1)
Total Supply Voltage................................................ 11V
Power Dissipation.............................................. 500mW
Operating Temperature
LTC1569C ............................................... 0°C to 70°C
LTC1569I............................................ –40°C to 85°C
Storage Temperature ............................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
TOP VIEW
NUMBER
+
IN
IN
1
2
3
4
8
7
6
5
OUT
–
+
LTC1569CS8-6
LTC1569IS8-6
V
GND
R
X
–
V
DIV/CLK
S8 PART
MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 150°C/W
15696
1569I6
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VS = 3V (V+ = 3V, V– = 0V), fCUTOFF = 64kHz, RLOAD = 10k unless otherwise specified.
PARAMETER
CONDITIONS
V = 5V, f
MIN
TYP
MAX
UNITS
Filter Gain
= 4.096MHz,
f
f
f
f
f
f
f
f
f
= 1280Hz = 0.02 • f
●
●
●
●
●
●
●
●
●
–0.05
–0.25
–0.65
–1.3
0.05
–0.15
–0.55
–1.0
–3.8
–60
–60
–62
–71
0.15
–0.05
–0.4
–0.7
–2.4
–40
–48
–50
–60
dB
dB
dB
dB
dB
dB
dB
dB
dB
S
CLK
IN
IN
IN
IN
IN
IN
IN
IN
IN
CUTOFF
CUTOFF
f
R
= 64kHz, V = 1.4V
= 10k, Pin 5 Shorted
,
= 12.8kHz = 0.2 • f
= 32kHz = 0.5 • f
CUTOFF
IN
P-P
EXT
CUTOFF
to Pin 4
= 51.2kHz = 0.8 • f
CUTOFF
= 64kHz = f
–5.3
CUTOFF
= 97.5kHz = 1.5 • f
= 97.5kHz = 1.5 • f
(LTC1569I)
(LTC1569C)
CUTOFF
CUTOFF
= 128kHz = 2 • f
= 192kHz = 3 • f
CUTOFF
CUTOFF
V = 2.7V, f
= 1MHz,
f
f
f
f
f
f
f
f
f
f
= 312Hz = 0.02 • f
CUTOFF
●
●
●
●
●
●
●
●
●
●
–0.12
–0.25
–0.65
–1.1
0.05
–0.15
–0.55
–0.9
–3.4
–54
–54
–60
–60
–66
0.16
–0.05
–0.4
–0.7
–3.2
–48
–50
–52
–55
–60
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
S
CLK
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
f
V
= 15.625kHz,
= 3125kHz = 0.2 • f
= 7812kHz = 0.5 • f
CUTOFF
CUTOFF
CUTOFF
CUTOFF
= 1V , Pin 6 Shorted
IN
P-P
to Pin 4, External Clock
= 12.5kHz = 0.8 • f
= 15.625kHz = f
–3.6
CUTOFF
= 23.44kHz = 1.5 • f
= 23.44kHz = 1.5 • f
(LTC1569I)
(LTC1569C)
(LTC1569I)
(LTC1569C)
CUTOFF
CUTOFF
= 31.25kHz = 2 • f
= 31.25kHz = 2 • f
= 46.88kHz = 3 • f
CUTOFF
CUTOFF
CUTOFF
Filter Phase
V = 2.7V, f
= 4MHz,
f
f
f
f
f
f
= 1250Hz = 0.02 • f
CUTOFF
–11
–111
82
–79
162
–91
Deg
Deg
Deg
Deg
Deg
Deg
S
CLK
IN
IN
IN
IN
IN
IN
f
= 62.5kHz, Pin 6
Shorted to Pin 4,
External Clock
= 12.5kHz = 0.2 • f
●
●
●
●
–114
79
–83
156
–108
85
–75
168
CUTOFF
CUTOFF
= 31.25kHz = 0.5 • f
CUTOFF
= 50kHz = 0.8 • f
CUTOFF
= 62.5kHz = f
CUTOFF
= 93.75kHz = 1.5 • f
CUTOFF
Filter Cutoff Accuracy
when Self-Clocked
R
= 10.24k from Pin 6 to Pin 7,
62.5kHz ±1%
EXT
V = 3V, Pin 5 Shorted to Pin 4
S
Filter Output DC Swing
(Note 6)
V = 3V, Pin 3 = 1.11V
2.1
3.9
8.5
V
V
S
P-P
P-P
●
●
1.9
3.7
V = 5V, Pin 3 = 2V
S
V
V
P-P
P-P
V = ±5V, Pin 5 Shorted to Pin 7, R
S
= 20k
V
LOAD
P-P
2
LTC1569-6
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VS = 3V (V+ = 3V, V– = 0V), fCLK = 4.096MHz, fCUTOFF = 64kHz, RLOAD = 10k unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output DC Offset
(Note 2)
R
R
= 10k, Pin 5 Shorted to Pin 7
= 10k, Pin 5 Shorted to Pin 7
V = 3V
±2
±6
±15
±5
±12
mV
mV
mV
EXT
S
V = 5V
S
V = ±5V
S
Output DC Offset
Drift
V = 3V
25
25
75
µV/°C
µV/°C
µV/°C
EXT
S
V = 5V
S
V = ±5V
S
Clock Pin Logic Thresholds
when Clocked Externally
V = 3V
S
Min Logical “1”
Max Logical “0”
2.7
0.5
V
V
V = 5V
S
Min Logical “1”
Max Logical “0”
4.0
0.5
V
V
V = ±5V
S
Min Logical “1”
Max Logical “0”
4.0
0.5
V
V
Power Supply Current
(Note 3)
f
= 256kHz (40k from Pin 6 to Pin 7,
V = 3V
3
4
5
mA
mA
CLK
S
Pin 5 Open, ÷ 4), f
= 4kHz
●
●
●
CUTOFF
V = 5V
S
3.5
4.5
5
6
mA
mA
V = 10V
S
7
8
mA
mA
f
= 4.096MHz (10k from Pin 6 to Pin 7,
V = 3V
8
9
mA
mA
mA
mA
CLK
S
Pin 5 Shorted to Pin 4, ÷ 1), f
= 64kHz
●
●
11
13
CUTOFF
V = 5V
S
V = 10V
S
12
mA
mA
●
17
Clock Feedthrough
Wideband Noise
THD
Pin 5 Open
0.1
95
80
64
mV
RMS
Noise BW = DC to 2 • f
µV
RMS
CUTOFF
f
= 3kHz, 1.5V , f
= 32kHz
dB
IN
P-P CUTOFF
Clock-to-Cutoff
Frequency Ratio
Max Clock Frequency
(Note 4)
V = 3V
5
5
7
MHz
MHz
MHz
S
V = 5V
S
V = ±5V
S
Min Clock Frequency
(Note 5)
V = 3V, 5V, T < 85°C
V = ±5V
S
1.5
3
kHz
kHz
S
A
Input Frequency Range
Aliased Components <–65dB
0.9 • f
Hz
CLK
Note 1: Absolute maximum ratings are those values beyond which the life
of a device may be impaired.
Note 4: The maximum clock frequency is arbitrarily defined as the
frequency at which the filter AC response exhibits >1dB of gain peaking.
Note 2: DC offset is measured with respect to Pin 3.
Note 5: The minimum clock frequency is arbitrarily defined as the frequecy
at which the filter DC offset changes by more than 5mV.
Note 6: For more details refer to the Input and Output Voltage Range
paragraph in the Applications Information section.
Note 3: If the internal oscillator is used as the clock source and the divide-
by-4 or divide-by-16 mode is enabled, the supply current is reduced as
much as 40% relative to the divide-by-1 mode.
3
LTC1569-6
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Passband Gain and Group Delay
vs Frequency
Gain vs Frequency
1
0
40
36
32
28
24
20
10
–10
–30
–50
–70
–90
–1
–2
–3
–4
2.5
10
100
1000
0.2
1
10
80
FREQUENCY (kHz)
FREQUENCY (kHz)
1569-6 G01
1569-6 GO2
THD vs Input Frequency
THD vs Input Voltage
–50
–55
–60
–65
–70
–75
–80
–85
–90
–60
–65
–70
–75
–80
–85
–90
V
= 3V
S
PIN 3 = 1.11V
V
= 5V
S
V
= 5V
S
PIN 3 = 2V
PIN 3 = 2V
V
= 1.5V
P-P
IN
f
f
= 3kHz
IN
f
= 32kHz
CUTOFF
+
= 32kHz
CUTOFF
IN TO OUT
+
IN TO OUT
0
5
10
15
20
25
30
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
INPUT FREQUENCY (kHz)
INPUT VOLTAGE (V
)
P-P
1569-6 G03
1569-6 G04
3V Supply Current
5V Supply Current
±5V Supply Current
14
12
10
8
10
9
11
10
9
8
DIV-BY-1
DIV-BY-1
DIV-BY-1
7
8
6
7
EXT CLK
EXT CLK
EXT CLK
5
6
4
DIV-BY-16
5
6
DIV-BY-4
DIV-BY-16
DIV-BY-4
DIV-BY-16
DIV-BY-4
3
4
4
2
3
0.1
1
10
100
0.1
1
10
100
0.1
1
f
10
100
f
(kHz)
f
(kHz)
(kHz)
CUTOFF
CUTOFF
CUTOFF
1569-6 G07
1569-6 G05
1569-6 G06
4
LTC1569-6
U
U
U
PIN FUNCTIONS
IN+/IN– (Pins 1, 2): Signals can be applied to either or
both input pins. The DC gain from IN+ (Pin 1) to OUT
(Pin 8)is1.0, andtheDCgainfromPin2toPin8is–1. The
input range, input resistance and output range are de-
scribed in the Applications Information section. Input
voltages which exceed the power supply voltages should
be avoided. Transients will not cause latchup if the current
into/out of the input pins is limited to 20mA.
DIV/CLK (Pin 5): DIV/CLK serves two functions. When the
internal oscillator is enabled, DIV/CLK can be used to
engage an internal divider. The internal divider is set to 1:1
whenDIV/CLKisshortedtoV– (Pin4). Theinternaldivider
is set to 4:1 when DIV/CLK is allowed to float (a 100pF
bypass to V– is recommended). The internal divider is set
to 16:1 when DIV/CLK is shorted to V+ (Pin 7). In the
divide-by-4 and divide-by-16 modes the power supply
current is reduced by as much as 40%.
GND (Pin 3): The GND pin is the reference voltage for the
filter and should be externally biased to 2V (1.11V) to
maximize the dynamic range of the filter in applications
usingasingle5V(3V)supply. Forsinglesupplyoperation,
the GND pin should be bypassed with a quality 1µF
ceramic capacitor to V– (Pin 4). The impedance of the
circuit biasing the GND pin should be less than 2kΩ as the
GND pin generates a small amount of AC and DC current.
For dual supply operation, connect Pin 3 to a high quality
DCground. Agroundplaneshouldbeused. Apoorground
will increase DC offset, clock feedthrough, noise and
distortion.
V–/V+ (Pins 4, 7): For 3V, 5V and ±5V applications a
quality 1µF ceramic bypass capacitor is required from V+
(Pin 7) to V– (Pin 4) to provide the transient energy for the
internal clock drivers. The bypass should be as close as
possible to the IC. In dual supply applications (Pin 3 is
grounded), an additional 0.1µF bypass from V+ (Pin 7) to
GND (Pin 3) and V– (Pin 4) to GND (Pin 3) is recom-
mended.
When the internal oscillator is disabled (RX shorted
to V–) DIV/CLK becomes an input pin for applying an
external clock signal. For proper filter operation, the clock
waveform should be a squarewave with a duty cycle as
close as possible to 50% and CMOS voltages levels (see
Electrical Characteristics section for voltage levels). DIV/
CLK pin voltages which exceed the power supply voltages
should be avoided. Transients will not cause latchup if the
faultcurrentinto/outoftheDIV/CLKpinislimitedto40mA.
RX (Pin6):ConnectinganexternalresistorbetweentheRX
pinandV+ (Pin7)enablestheinternaloscillator. Thevalue
oftheresistordeterminesthefrequencyofoscillation. The
maximum recommended resistor value is 40k and the
minimum is 3.8k. The internal oscillator is disabled by
shorting the RX pin to V– (Pin 4). (Please refer to the
Applications Information section.)
OUT (Pin 8): Filter Output. This pin can drive 10kΩ and/or
40pF loads. For larger capacitive loads, an external 100Ω
series resistor is recommended. The output pin can ex-
ceed the power supply voltages by up to ±2V without
latchup.
ThemaximumvoltagedifferencebetweenGND(Pin3)and
V+ (Pin 7) should not exceed 5.5V.
5
LTC1569-6
W
BLOCK DIAGRA
+
IN
IN
1
2
3
4
8
7
6
5
OUT
10TH ORDER
LINEAR PHASE
FILTER NETWORK
–
+
V
R
EXT
POWER
CONTROL
GND
R
X
DIVIDER/
BUFFER
–
V
DIV/CLK
PRECISION
OSCILLATOR
1569-6 BD
U
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APPLICATIONS INFORMATION
Table1. fCUTOFF vs REXT, VS = 3V, TA = 25°C, Divide-by-1 Mode
Self-Clocking Operation
R
Typical f
Typical Variation of f
±3.0%
EXT
CUTOFF
CUTOFF
The LTC1569-6 features a unique internal oscillator which
sets the filter cutoff frequency using a single external
resistor. The design is optimized for VS = 3V, fCUTOFF
3844Ω*
5010Ω*
10k
N/A
N/A
±2.5%
=
64kHz
32kHz
16kHz
±1%
64kHz, 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 1kHz to
64kHz. 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.
20.18k
40.2k
±2.0%
±3.5%
*R values less than 10k can be used only in the divide-by-16 mode.
EXT
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 LTC1569-6 is in the divide-by-4
and divide-by-16 modes the power is automatically re-
duced. This results in up to a 40% power savings.
+
IN
IN
OUT
1
2
8
7
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).
–
+
V
R
LTC1569-6
GND
EXT
3
4
6
5
.
R
X
DIVIDE-BY-16
DIVIDE-BY-4
100pF
+
–
V
V
–
V
DIV/CLK
The cutoff frequency is easily estimated from the equation
in Figure 1. Examples 1 and 2 illustrate how to use the
graphs in Figures 2 through 7 to get a more precise
estimate of the cutoff frequency.
64kHz (10k/R
)
EXT
f
=
CUTOFF
DIVIDE-BY-1
1, 4 OR 16
1569-6 F01
Figure 1
Example 1: LTC1569-6, REXT = 20k, VS = 3V, divide-by-16
mode,DIV/CLK(Pin 5)connectedtoV+ (Pin7),TA =25°C.
6
LTC1569-6
U
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APPLICATIONS INFORMATION
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 64kHz • (10k/20k)
• (1/16) = 2kHz.
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 64kHz • (10k/10k)
• (1/1) = 64kHz.
For a more precise fCUTOFF estimate, use Table 1 to get
a value of fCUTOFF when REXT = 20k and use the graph
in Figure 6 to find the correct divide ratio when VS = 3V
and REXT = 20k. Based on Table 1 and Figure 6, fCUTOFF
= 32kHz • (20.18k/20k) • (1/16.02) = 2.01kHz.
For a more precise fCUTOFF estimate, use Figure 2 to
correct for the supply voltage when VS = 5V. From
Table 1 and Figure 2, fCUTOFF = 64k • (10k/10k) • 0.970
= 62.1kHz.
The oscillator is sensitive to transients on the positive
supply. The IC should be soldered to the PC board and the
PCB layout should include a 1µF ceramic capacitor be-
tween V+ (Pin 7) and V– (Pin 4) , as close as possible to
theICtominimizeinductance. Avoidparasiticcapacitance
on RX and avoid routing noisy signals near RX (Pin 6). Use
From Table 1, the part-to-part variation of fCUTOFF will
be ±2%. From the graph in Figure 7, the 0°C to 70°C
drift of fCUTOFF will be –0.2% to 0.2%.
Example 2: LTC1569-6, REXT = 10k, VS = 5V, divide-by-1
mode,DIV/CLK(Pin 5)connectedtoV– (Pin4),TA =25°C.
1.04
1.010
R
R
R
R
= 5k
V
V
V
= 3V
= 5V
= 10V
EXT
EXT
EXT
EXT
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
S
S
S
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
= 10k
= 20k
= 40k
2
4
6
8
10
–50
–25
0
25
50
75
100
V
(V)
TEMPERATURE (°C)
SUPPLY
1569-6 F02
1569-6 F03
Figure 3. Filter Cutoff vs Temperature,
Divide-by-1 Mode, REXT = 10k
Figure 2. Filter Cutoff vs VSUPPLY
Divide-by-1 Mode, TA = 25°C
,
4.08
4.04
4.00
3.96
1.010
R
R
R
R
= 5k
V
V
V
= 3V
= 5V
= 10V
EXT
EXT
EXT
EXT
S
S
S
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
= 10k
= 20k
= 40k
2
4
6
8
10
–50
–25
0
25
50
75
100
V
(V)
TEMPERATURE (°C)
SUPPLY
1569-6 F04
1569-6 F05
Figure 5. Filter Cutoff vs Temperature,
Divide-by-4 Mode, REXT = 10k
Figure 4. Typical Divide Ratio in the
Divide-by-4 Mode, TA = 25°C
7
LTC1569-6
APPLICATIONS INFORMATION
U
W U U
16.32
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
R
R
R
R
= 5k
V
V
V
= 3V
= 5V
= 10V
EXT
EXT
EXT
EXT
S
S
S
= 10k
= 20k
= 40k
16.16
16.00
15.84
2
4
6
8
10
–50
–25
0
25
50
75
100
V
(V)
TEMPERATURE (°C)
SUPPLY
1569-6 F06
1569-6 F07
Figure 6. Typical Divide Ratio in the
Divide-by-16 Mode, TA = 25°C
Figure 7. Filter Cutoff vs Temperature,
Divide-by-16 Mode, REXT = 10k
a ground plane connected to V– (Pin 4) for single supply
applications. Connect a ground plane to GND (Pin 3) for
dual supply applications and connect V– (Pin 4) to a
copper trace with low thermal resistance.
input signal at IN+ should be centered around the DC
voltageatIN–. TheinputcanalsobeACcoupled, asshown
in the Typical Applications section.
For inverting single-ended filtering, connect IN+ to GND or
to quiet DC reference voltage. Apply the signal to IN–. The
DCgainfromIN– toOUTis–1,assumingIN– isreferenced
to IN+ and OUT is reference to GND.
Input and Output Voltage Range
The input signal range includes the full power supply
range. The output range is typically (V– + 50mV) to (V+ –
0.8V) when using a single 3V supply with the GND (Pin 3)
voltage set to 1.11V. In other words, the output range is
typically 2.1VP-P for a 3V supply. Similarly, the output
range is typically 3.9VP-P for a single 5V supply when the
GND (Pin 3) voltage is 2V. For ±5V supplies, the output
Refer to the Typical Performance Characteristics section
to estimate the THD for a given input level.
Dynamic Input Impedance
TheuniqueinputsamplingstructureoftheLTC1569-6has
a dynamic input impedance which depends on the con-
figuration, i.e., differential or single-ended, and the clock
frequency. The equivalent circuit in Figure 8 illustrates the
input impedance when the cutoff frequency is 64kHz. For
other cutoff frequencies replace the 125k value with
125k • (64kHz/fCUTOFF).
When driven with a single-ended signal into IN– with IN+
tied to GND, the input impedance is very high (~10MΩ).
When driven with a single-ended signal into IN+ with IN–
tiedtoGND,theinputimpedanceisa125kresistortoGND.
When driven with a complementary signal whose com-
mon mode voltage is GND, the IN+ input appears to have
125k to GND and the IN– input appears to have –125k to
GND. To make the effective IN– impedance 125k when
driven differentially, place a 62.5k resistor from IN– to
GND. For other cutoff frequencies use 62.5k • (64kHz/
range is typically 8.5VP-P
.
The LTC1569-6 can be driven with a single-ended or
differential signal. When driven differentially, the voltage
between IN+ and IN– (Pin 1 and Pin 2) is filtered with a DC
gain of 1. The single-ended output voltage OUT (Pin 8) is
referenced to the voltage of the GND (Pin 3). The common
mode voltage of IN+ and IN– can be any voltage that keeps
the input signals within the power supply range.
For noninverting single-ended applications, connect IN–
to GND or to a quiet DC reference voltage and apply the
input signal to IN+. If the input is DC coupled then the DC
gain from IN+ to OUT will be 1. This is true given IN+ and
OUT are referenced to the same voltage, i.e., GND, V– or
some other DC reference. To achieve the distortion levels
shown in the Typical Performance Characteristics the
8
LTC1569-6
U
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APPLICATIONS INFORMATION
fCUTOFF), asshownintheTypicalApplicationssection. The
typical variation in dynamic input impedance for a given
clock frequency is ±10%.
DC Accuracy
DC accuracy is defined as the error in the output voltage
after DC offset and DC gain errors are removed. This is
similar to the definition of the integral nonlinearity in A/D
converters.Forexample,aftermeasuringvaluesofVOUT(DC)
vs VIN(DC) for a typical LTC1569-6, a linear regression
shows that VOUT(DC) = VIN(DC) • 0.99854 + 0.00134V is the
straight line that best fits the data. The DC accuracy
describes how much the actual data deviates from this
straightline(i.e.,DCERROR=VOUT(DC) –(VIN(DC) •0.99854
+ 0.00134V). In a 12-bit system with a full-scale value of
2V, the LSB is 488µV. Therefore, if the DCERROR of the
filter is less than 488µV over a 2V range, the filter has
12-bit DC accuracy. Figure 9 illustrates the typical DC
accuracy of the LTC1569-6 on a single 5V supply.
Wideband Noise
The wideband noise of the filter is the RMS value of the
device’s output noise spectral density. The wideband
noise data is used to determine the operating signal-to-
noise at a given distortion level. The wideband noise is
nearly independent of the value of the clock frequency and
excludes the clock feedthrough. Most of the wideband
noise is concentrated in the filter passband and cannot be
removed with post filtering (Table 2). Table 3 lists the
typical wideband noise for each supply.
Table 2. Wideband Noise vs Supply Voltage, Single 3V Supply
Bandwidth
DC to f
Total Integrated Noise
DC Offset
80µV
95µV
CUTOFF
RMS
RMS
DC to 2 • f
The output DC offset of the LTC1569-6 is trimmed to less
CUTOFF
than ±5mV. The trimming is performed with VS = 1.9V,
DC to f
110µV
RMS
CLK
–1.1V with the filter cutoff frequency set to 4kHz (REXT
=
10k, DIV/CLKshortedtoV+). ToobtainoptimumDCoffset
performance, appropriate PC layout techniques should be
used. The filter IC should be soldered to the PC board. The
power supplies should be well decoupled including a 1µF
ceramic capacitor from V+ (Pin 7) to V– (Pin 4). A ground
plane should be used. Noisy signals should be isolated
from the filter input pins.
Table 3. Wideband Noise vs Supply Voltage, fCUTOFF = 64kHz
Total Integrated Noise
Power Supply
DC to 2 • f
CUTOFF
3V
95µV
RMS
5V
100µV
105µV
RMS
RMS
±5V
Clock Feedthrough
When the power supply is 3V, the output DC offset should
change less than ±2mV when the clock frequency varies
from 64kHz to 4096kHz. When the clock frequency is
fixed, the output DC offset will typically change by less
than ±3mV (±15mV) when the power supply varies from
3V to 5V (±5V) in the divide-by-1 mode. In the divide-by-
4ordivide-by-16modes,theoutputDCoffsetwilltypically
change less than –9mV (–27mV) when the power supply
varies from 3V to 5V (±5V). The offset is measured with
respect to GND (Pin 3).
ClockfeedthroughisdefinedastheRMSvalueoftheclock
frequency and its harmonics that are present at the filter’s
OUT pin (Pin 8). The clock feedthrough is measured with
IN+ and IN– (Pins 1 and 2) grounded and depends on the
PCboardlayoutandthepowersupplydecoupling. Table 4
shows the clock feedthrough (the RMS sum of the first 11
harmonics) when the LTC1569-6 is self-clocked with
R
EXT =10k, DIV/CLK(Pin5)open(divide-by-4mode). The
clock feedthrough can be reduced with a simple RC post
filter.
Aliasing
Table 4. Clock Feedthrough
Power Supply
Feedthrough
Aliasing is an inherent phenomenon of sampled data
filters. In lowpass filters significant aliasing only occurs
when the frequency of the input signal approaches the
sampling frequency or multiples of the sampling fre-
3V
0.1mV
0.3mV
0.9mV
RMS
RMS
RMS
5V
±5V
9
LTC1569-6
U
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APPLICATIONS INFORMATION
quency. The LTC1569-6 samples the input signal twice
every clock period. Therefore, the sampling frequency is
twice the clock frequency and 128 times the filter cutoff
frequency. Input signals with frequencies near 2 • fCLK
± fCUTOFF will be aliased to the passband of the filter and
appear at the output unattenuated.
488
244
0
–
IN
+
2
+
–
IN – GND
125k
i =
–
+
8
OUT
125k
–244
V
= 5V
EXT
= 25°C
S
125k
R
= 10k
+
1
IN
–
+
T
A
–488
–1.5 –1.0 –0.5
0
0.5
1.0
1.5
3
GND
V
DC (V)
1569-6 F06
IN
1569-6 F09
Figure 8
Figure 9
U
TYPICAL APPLICATIO S
Single 3V, AC Coupled Input,
64kHz Cutoff Frequency
Single 3V Operation, AC Coupled Input,
64kHz Cutoff Frequency
0.1µF
1
2
8
7
+
–
32µs
28µs
24µs
V
IN
IN
OUT
V
IN
OUT
R
= 10k
3V
EXT
+
3V
1µF
V
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
10k 20k 30k 40k 50k 60k 70k
LTC1569-6
GND
3.48k
2k
3
4
6
5
R
X
1µF
–
V
DIV/CLK
1569-6 TA02
64kHz
n = 1
10k
f
=
CUTOFF
(
)(
R
)
EXT
n = 1, 4, 16 FOR PIN 5 AT
+
0
40k 50k 60k 70k 80k 90k 100k 110k 120k 130k 140k 150k
FREQUENCY (Hz)
GROUND, OPEN, V
1569-6 TA02a
10
LTC1569-6
U
TYPICAL APPLICATIO S
Single 3V Supply Operation, DC Coupled,
16kHz Cutoff Frequency
Single 5V Operation, 50kHz Cutoff Frequency,
DC Coupled Differential Inputs with Balanced Input Impedance
1
2
8
7
+
–
1
2
8
7
+
–
+
–
V
V
V
IN
IN
OUT
V
IN
IN
IN
OUT
V
OUT
IN
IN
OUT
R
= 10k
3V
R
EXT
= 12.8k
5V
IN
EXT
+
+
3V
1µF
V
5V
1µF
V
LTC1569-6
GND
3.48k
2k
LTC1569-6
GND
80.6k
3
LT®1460-2.5
(SOT-23)
3
4
6
5
6
5
R
R
OUT
GND
X
X
1µF
1µF
4
–
–
V
DIV/CLK
V
DIV/CLK
1569-6 TA03
100pF
64kHz
n = 4
10k
64kHz
n = 1
10k
1569-6 TA04
f
=
f
~
CUTOFF
CUTOFF
(
)(
R
)
(
)(
)
12.8k
EXT
n = 1, 4, 16 FOR PIN 5 AT
n = 1, 4, 16 FOR PIN 5 AT
+
+
GROUND, OPEN, V
GROUND, OPEN, V
±5V Supply Operation, DC Coupled Filter
with External Clock Source
1
2
8
7
+
–
V
IN
IN
OUT
V
OUT
CUTOFF CLK
IN
f
= f /64
+
5V
V
0.1µF
LTC1569-6
GND
3
6
5
R
–5V
X
0.1µF
4
–
5V
0V
V
DIV/CLK
–5V
f
≤ 5MHz
CLK
1569-6 TA05
1µF
Pulse Shaping Circuit for Single 3V Operation,
128kbps 2-Level Data, 64kHz Cutoff Filter
2-Level, 128kbps Eye Diagram
3V
20k
1
8
+
IN
OUT
V
OUT
128ksps
DATA
LTC1569-6
–
7.32k*
R
EXT
= 10k
3V
2
3
7
6
+
3V
1µF
IN
V
20k
3.48k
2k
GND
R
X
1µF
4
5
–
V
DIV/CLK
1569-6 TA06
* SEE APPLICATIONS INFORMATION, “INPUT AND OUTPUT VOLTAGE RANGE”
2µs/DIV
1569-6 TA08
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LTC1569-6
TYPICAL APPLICATIO S
U
Pulse Shaping Circuit for Single 3V Operation,
200kbps (100ksps) 4-Level Data, 64kHz Cutoff Filter
4-Level, 200kbps (100ksps) Eye Diagram
3V
20k
1
8
+
IN
OUT
V
OUT
D1
D0
LTC1569-6
–
2.49k*
9.31k*
100ksps
DATA
R
EXT
= 10k
3V
2
3
7
6
+
3V
1µF
IN
V
3.48k
2k
20k
GND
R
X
1µF
4
5
–
V
DIV/CLK
1569-6 TA06
* SEE APPLICATIONS INFORMATION, “INPUT AND OUTPUT VOLTAGE RANGE”
2µs/DIV
1569-6 TA09
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
(0.254 – 0.508)
7
5
8
6
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
3
4
2
SO8 1298
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1064-3
Linear Phase, Bessel 8th Order Filter
Linear Phase, 8th Order Lowpass Filter
Linear Phase, 8th Order Lowpass Filter
Low Power, Linear Phase Lowpass Filter
Linear Phase, 8th Order Lowpass Filter
Universal, 8th Order Active RC Filter
f
f
f
f
f
/f
= 75/1 or 150/1, Very Low Noise
CLK CUTOFF
LTC1064-7
/f
= 50/1 or 100/1, f
= 100kHz
CUTOFF(MAX)
CLK CUTOFF
LTC1069-7
/f
= 25/1, f
= 200kHz, SO-8
CUTOFF(MAX)
CLK CUTOFF
LTC1164-7
/f
= 50/1 or 100/1, I = 2.5mA, V = 5V
CLK CUTOFF
S
S
LTC1264-7
/f
= 25/1 or 50/1, f
= 200kHz
CLK CUTOFF
CUTOFF(MAX)
LTC1562/LTC1562-2
f
f
= 150kHz (LTC1562)
= 300kHz (LTC1562-2)
CUTOFF(MAX)
CUTOFF(MAX)
LTC1563-2/LTC1563-3
LTC1569-7
Active RC, 4th Order Lowpass
f
f
= 300kHz, Very Low Noise
CUTOFF(MAX)
CUTOFF(MAX)
Linear Phase DC Accurate, 10th Order
= 300kHz, No Clock Required
15696f LT/TP 0500 4K • PRINTED IN THE USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
LINEAR TECHNOLOGY CORPORATION 1999
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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