MAX1474 [MAXIM]
Miniature Electronically Trimmable Capacitor; 微型电子微调电容器
| 型号： | MAX1474 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Miniature Electronically Trimmable Capacitor |
| 文件： | 总8页 (文件大小：139K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1948; Rev 1; 3/01
Miniature Electronically Trimmable Capacitor
General Description
Features
The MAX1474 is a fine-line (geometry) electronically trim-
mable capacitor (FLECAP) programmable through a
simple digital interface. There are 32 programmable
capacitance values ranging from 6.4pF to 13.3pF in
0.22pF increments (Table 1). The quartz dielectric
capacitance is highly stable and exhibits a very low volt-
age coefficient. It has virtually no dielectric absorption
and has a very low temperature drift coefficient
(<33ppm/°C). The MAX1474 is programmed through two
digital interface pins, which have Schmidt triggers and
pulldown resistors to secure capacitance programming.
ꢀ Tiny SC70 Package (1.1mm x 2.2mm x 2.4mm)
ꢀ High-Performance Electronically Trimmable
Capacitance
ꢀ Very Simple Digital Interface
ꢀ Eliminates the Need for Mechanical Tuning
ꢀ Enabling Technology for Low-Cost Production
Line Automation
ꢀ Fully Static Operation After Programming
(No Switching)
Customization
Maxim can customize the MAX1474 for specific high-
volume applications. Contact Maxim for further informa-
tion.
Applications
Post-Trim of Low-Cost Regenerative Receivers
Ordering Information
PIN-
TOP
MARK
AAT
PART
TEMP. RANGE
Tunable RF Stages
PACKAGE
MAX1474AXT-T -40°C to +125°C 6 SC70-6
Low-Cost, Low-Temperature Drift Oscillators
Garage Door Openers
Keyless Entry
Functional Diagram
Industrial Wireless Control
Capacitive Sensor Trimming
RFID Tags
0.2pF
CP
CM
0.4pF
6pF
6pF
Pin Configuration
0.8pF
1.6pF
TOP VIEW
MAX1474
V
SS
V
DD
CP
1
2
3
6
5
4
CM
3.2pF
V
V
SS
DD
EN
DAT
EN
LOGIC INTERFACE
DAT
SC70
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Miniature Electronically Trimmable Capacitor
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
to V ..................................... -0.3V to +6V
Operating Temperature Range
DD
SS
All Other Pins ...................................(V - 0.3V) to (V
RMS Current into Any Pin....................................................50mA
+ 0.3V)
MAX1474AXT................................................-40°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
SS
DD
Continuous Power Dissipation (T = +70°C)
A
6-Pin SC70 (derate 3.1mW/°C above +70°C).............245mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL CHARACTERISTICS
Supply Voltage
2.7
5.5
10
V
Normal DC operation only, EN, DAT pins
During programming at 1MHz
Supply Current
µA
µA
Supply Current
200
CAPACITOR CHARACTERISTICS
Self-Resonant Frequency
Quality Factor
SRF
Q
15 DAT pulses
960
12
MHz
f = 315MHz
0
Absolute Accuracy
15
%
Capacitance Increments (Note 1)
Capacitance at 0 DAT Pulses (Note 1)
0.22
6.4
pF
pF
C
MIN
Capacitance Range (Note 1)
C
- C
6.9
33
pF
MAX
MIN
Temperature Drift
ppm/°C
DIGITAL CHARACTERISTICS
0.25 x
Low-Level Input Voltage
High-Level Input Voltage
V
V
V
IL
V
DD
0.75 x
V
IH
V
DD
Input Pulldown Resistor
50
kΩ
Input Leakage Current
200
µA
TIMING CHARACTERISTICS
Maximum Clock Rate on DAT
Minimum DAT High Pulse Width
Minimum Setup Time for DAT
Minimum Data Load Time
Minimum Reset Time
f
25
20
20
20
20
MHz
ns
DAT
t
DAT_HIGH
t
t
ns
SETUP
t
ns
LOAD
ns
RESET
Note 1: Measurements made at CP with CM = GND.
2
_______________________________________________________________________________________
Miniature Electronically Trimmable Capacitor
Typical Operating Characteristics
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
CAPACITANCE vs. VOLTAGE
(DIFFERENTIAL)
CAPACITANCE vs. VOLTAGE
(SINGLE ENDED)
CAPACITANCE vs. TEMPERATURE
16.0
15.6
15.2
14.8
14.4
14.0
11.10
11.05
11.00
10.95
10.90
11.00
10.99
10.98
10.97
10.96
10.95
10.94
10.93
10.92
10.91
10.90
DAT = 31 PULSES
DAT = 31 PULSES,
SEE FIGURE 3a.
DAT = 31 PULSES,
CC
SEE FIGURE 3b.
V
= +5V,
V
= +3.3V
CC
V
= +5V
CC
0
1
2
3
4
5
-40 -15
10
35
60
85
110 125
-5 -4 -3 -2 -1
0
1
2
3
4
5
VOLTAGE (V)
TEMPERATURE (°C)
VOLTAGE (V)
EFFECTIVE CAPACITANCE
vs. FREQUENCY
QUALITY FACTOR vs. FREQUENCY
QUALITY FACTOR vs. CAPACITANCE
20
39
36
33
30
27
24
21
18
15
12
9
100
10
1
18
16
31 DAT PULSES
14
12
10
8
15 DAT PULSES
0 DAT PULSES
6
4
2
6
0
50 200 350 500 650 800 950 1100
FREQUENCY (MHz)
10
100
1000
6
7
8
9
10 11 12 13 14
FREQUENCY (MHz)
CAPACITANCE (pF)
SMITH CHART:
0 DAT PULSES
SELF-RESONANT
FREQUENCY vs. DAT PULSES
1200
1150
1100
1050
f
1
1000
950
900
850
800
0
4
8
12 16 20 24 28 32
DAT PULSES
f = 1200MHz
1
_______________________________________________________________________________________
3
Miniature Electronically Trimmable Capacitor
Typical Operating Characteristics (continued)
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
DD
SS
A
SMITH CHART:
15 DAT PULSES
SMITH CHART:
31 DAT PULSES
f
1
f
1
f = 962MHz
1
f = 848MHz
1
Pin Description
PIN
1
NAME
FUNCTION
Capacitor Pin Connected to High-Impedance Node. See Detailed Description.
Positive Supply Pin. Connect a 0.01µF capacitor to V
CP
2
V
.
SS
DD
3
EN
Programming Enable Pin. Has an internal 50kΩ pulldown resistor to V
.
SS
4
DAT
Programming Data Pin. Has an internal 50kΩ pulldown resistor to V
.
SS
5
V
Negative Supply Pin
SS
6
CM
Capacitor Pin Connected to Low-Impedance Node. See Detailed Description.
0.42pF to 10.9pF in 0.34pF steps. If one terminal is
Detailed Description
grounded, and the capacitance is measured to ground,
the parasitics inherent in the package will become
lumped with the switched array, allowing tuning from
6.4pF to 13.3pF in 0.22pF steps. When using the
MAX1474, it is recommended for optimal performance
to connect the CM terminal to the lowest impedance
node (i.e., ground or supply if possible) and CP to the
higher impedance node (i.e., the resonant node in a
ground-referenced LC tank circuit).
The MAX1474 consists of a binary-weighted array of
capacitors that can be switched in and out of parallel to
provide 32 monotonic steps. The switches implement-
ed allow the DC bias of either terminal of the capacitor
to be anywhere from ground to the supply voltage.
There is no inherent polarity. The signal swing range is
limited to 300mV above V
and 300mV below V
.
SS
DD
Therefore, if a large-signal swing range is desired, care
must be taken to bias the terminal(s) requiring high
swing capability near midsupply.
Digital Interface
The digital interface sets the desired capacitance
value. There are only two pins, EN and DAT, required
for this operation. EN is an active-high control signal.
If the capacitance is measured differentially from one
terminal to the other, the greatest min/max ratio of the
binary array can be realized, allowing tuning from
4
_______________________________________________________________________________________
Miniature Electronically Trimmable Capacitor
While EN is asserted, the internal counter counts posi-
tive edges of DAT. The number of sequential pulses on
DAT determines the capacitance setting. As EN is de-
asserted, the counter value is latched into the capaci-
tance control registers first, and then the counter is set
to zero. The programmed capacitance value then
appears between CP and CM. During the period when
EN is asserted, the capacitance value between CP and
CM stays unchanged. Figure 1 is a digital timing dia-
gram.
The FLECAP zero step differential capacitance is low,
typically 0.42pF. The parasitic capacitances are the
reason for the 6pF of input capacitance and the
decrease in range when configured as a single-ended
capacitor. The MAX1474 is an excellent choice in appli-
cations where only differential capacitance matters.
Table 1. Capacitance Values
TYPICAL
VALUES
(CM = GND)
(pF)
TYPICAL
VALUES
(DIFFERENTIAL)
(pF)
NUMBER OF
PULSES ON
DAT
Q Enhancement Circuit
Since the capacitors have the multiplexer series resis-
tance associated with them, the quality factor of the
trimmable capacitors is not high. For example, a 10pF
capacitor only has a theoretical Q of about 10 at
315MHz with 5Ω series resistance. As in Figure 2, an
impedance transformer-like circuit is needed to over-
come this low Q. With this circuit, a much higher Q is
achievable using high-Q external capacitors. This con-
figuration allows a tuning range of approximately
314MHz to 319MHz with 160kHz steps when resonated
with a 27nH inductor. Figure 2 shows a Q enhancement
circuit.
0
6.41
6.63
0.424
0.769
1.11
1.45
1.79
2.13
2.47
2.81
3.13
3.48
3.82
4.16
4.49
4.84
5.18
5.52
5.84
6.18
6.53
6.87
7.20
7.54
7.88
8.22
8.55
8.89
9.24
9.58
9.91
10.25
10.59
10.93
1
2
6.86
3
7.09
4
7.31
5
7.54
6
7.78
7
8.00
8
8.22
9
8.45
Startup Sequence
The MAX1474 must be programmed before use. When
powered up, the following sequence must occur:
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
8.67
8.90
9.12
• Deassert both EN and DAT.
• Assert EN.
9.34
9.57
• Send pulses on DAT. The total number of pulses
9.77
determines the capacitance value (Table 1).
10.02
10.25
10.47
10.67
10.87
11.10
11.33
11.57
11.80
12.02
12.24
12.46
12.68
12.91
13.14
13.33
• Deassert EN.
Applications Information
The MAX1474 offers users a wide range of applica-
tions, including trimming of regenerative receivers,
oscillators, RFID tags, and capacitive sensors. A
capacitive sensor is usually made of two capacitors.
One capacitor (CM) changes with the sensed function,
such as pressure, acceleration, or humidity. The sec-
ond capacitor (CR) is used as a reference capacitance
that does not vary with the sensed function. In most
applications, it is needed to detect the difference
between these capacitance values. Due to manufactur-
ing tolerances, there are normally offsets between CM
and CR, which can easily be nulled out by the FLECAP
as shown in Figure 4.
To increase the adjustment capacitance range, several
FLECAPs can be placed in parallel. Several capacitors
can be tied together to increase the number of steps or
the resolution, as shown in Figures 5a and 5b.
_______________________________________________________________________________________
5
Miniature Electronically Trimmable Capacitor
Test Circuits/Timing Diagrams
EN
DAT
t
LOAD
t
SETUP
t
COUNT
RESET
t
SETUP
t
DAT_HIGH
Figure 1. Digital Timing Diagram
CAPACITANCE METER
f = 1MHz
CM
0.01µF
2MΩ
12pF
CP
C : 9.3 TO
IN
V
GEN
9.6pF
35pF
C: 6.41 TO
13.33pF
MAX1474
V
V
DD
SS
EN
DAT
Figure 2. Q Enhancement Circuit
Figure 3a. Capacitance vs. Voltage (Single Ended)
6
_______________________________________________________________________________________
Miniature Electronically Trimmable Capacitor
Test Circuits/Timing Diagrams (continued)
CAPACITANCE METER
C
FIXED
0.01µF
2MΩ
0.01µF
CP
V
CM
V
V
GEN1
MAX1474
GEN1
V
MAX1474
MAX1474
V
DD
SS
+ V
= V
DD
GEN1
GEN2
EN
DAT
Figure 5b. Increasing Capacitance Range and Resolution
Figure 3b. Capacitance vs. Voltage (Differential)
Chip Information
CR
TRANSISTOR COUNT: 634
CM
CS
MAX1474
Figure 4. Electronic Offset Trimming
CP
V
CM
V
DD
SS
MAX1474
EN
DAT
CP
V
CM
V
DD
SS
MAX1474
EN
DAT
Figure 5a. Increasing Capacitance Range
_______________________________________________________________________________________
7
Miniature Electronically Trimmable Capacitor
Package Information
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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