SILICON DESIGNS, INC
Model 1221
LOW NOISE ANALOG ACCELEROMETER
SENSOR: Capacitive Micromachined
Nitrogen Damped
Hermetically Sealed
___
Low Noise: 5 g/Hz typical for
2g Full Scale Version
Internal Temperature Sensor
±4V Differential Output or
0.5V to 4.5V Single Ended Output
Fully Calibrated
Responds to DC & AC Acceleration
-55 to +125 °C Operation
+5 VDC, 8 mA Power (typical)
Non-Standard g Ranges Available
Integrated Sensor & Amplifier
LCC or J-Lead Surface
Mount Package
Serialized for Traceability
Pin Compatible with Model 1210
'(6&5,37,21
ORDERING INFORMATION
Full Scale
Acceleration
±2 g
±5 g
±10 g
±25 g
±50 g
±100 g
±200 g
±400 g
Hermetic Packages
20 pin LCC
20 pin JLCC
1221L-002
1221J-002
1221L-005
1221J-005
1221L-010
1221J-010
1221L-025
1221J-025
1221L-050
1221J-050
1221L-100
1221J-100
1221L-200
1221J-200
1221L-400
1221J-400
The Model 1221 is a low-cost, integrated accelerometer for use in zero to medium frequency instrumentation
applications that require extremely low noise. The 2g version is ideally suited for seismic applications. Each
miniature, hermetically sealed package combines a micro-machined capacitive sense element and a custom
integrated circuit that includes a sense amplifier and differential output stage. It is relatively insensitive to temperature
changes and thermal gradients. Each device is marked with a serial number on its bottom surface for traceability.
An optional calibration test sheet (1221-TST) is also available which lists the measured bias, scale factor, linearity, operating
current and frequency response.
23(5$7,21
The Model 1221 produces two analog output voltages which vary with acceleration as shown in the figure below. The
outputs can be used either in differential or single ended mode referenced to +2.5 volts. Two reference voltages, +5.0
and +2.5 volts (nominal), are required; the output scale factor is ratiometric to the +5 volt reference voltage, and both
outputs at zero acceleration are equal to the +2.5 volt reference. The sensitive axis is perpendicular to the bottom
of the package, with positive acceleration defined as
a force pushing on the bottom of the package.
$33/,&$7,216
Seismic Monitoring
Earthquake Detection
Security Systems
Machine Control
Modal Analysis
Instrumentation
Appliances
Robotics
Crash Testing
Vibration Monitoring
Vibration Analysis
Vehicle Dynamics
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 1]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
Model 1221 Low Noise Analog Accelerometer
6,*1$/'(6&5,37,216
VDD and GND (power): Pins (9,11,14) and (2,5,6,18,19) respectively. Power (+5 Volts DC) and ground.
AOP and AON (output): Pins 12 and 16 respectively. Analog output voltages proportional to acceleration. The AOP voltage
increases (AON decreases) with positive acceleration; at zero acceleration both outputs are nominally equal to the +2.5 volt
reference. The device experiences positive (+1g) acceleration with its lid facing up in the earth’s gravitational field. Either
output can be used individually or the two outputs can be used differentially but differential mode is recommended for both
lowest noise and highest accuracy operation. Voltages can be measured ratiometrically to VR for good accuracy without
requiring a precision reference voltage. (See plot.)
DV (input): Pin 4. Deflection Voltage. Normally left open. A test input that applies an electrostatic force to the sense element,
simulating a positive acceleration. The nominal voltage at this pin is ½ VDD. DV voltages higher than required to bring the
output to positive full scale may cause device damage.
VR (input): Pin 3. Voltage Reference. Tie directly to VDD for ratiometric measurements or to a +5V reference for better absolute
accuracy. A 0.1F bypass capacitor is recommended at this pin.
2.5 Volt (input): Pin 17. Voltage Reference. Tie to a resistive voltage divider from +5 volts or to a +2.5 volt reference voltage.
IT (output): Pin 8. Temperature dependent current source. (May be tied to VDD; see full description on page 5).
3(5)250$1&( - by Model:
MODEL NUMBER
VDD=VR=5.0 VDC, TC=25°C.
1221x-002 1221x-005 1221x-010 1221x-025 1221x-050 1221x-100 1221x-200 1221x-400
Input Range
±2
Frequency Response (Nominal, 3 dB) 0 - 400
2000
Sensitivity (Differential) 1
Output Noise (Differential, RMS, typical)
5
Max. Mechanical Shock (0.1 ms)
3(5)250$1&( - all Models:
±5
±10
±25
±50
±100
±200
±400
g
0 - 600 0 - 1000 0 - 1500 0 - 2000 0 - 2500 0 - 3500 0 - 4000
Hz
800
400
160
80
40
20
10
mV/g
7
10
25
50
100
200
400
g/(root Hz)
2000
g
Note 1: Single ended sensitivity is half of values shown.
Unless otherwise specified VDD=VR=5.0 VDC, TC=25°C, Differential Mode.
PARAMETER
MIN
Cross Axis Sensitivity
Bias Calibration Error 2
Bias Temperature Shift
(TC= -55 to +125°C) 2
UNITS
-002
-005 thru -200
-002
-005 thru -200
Scale Factor Calibration Error 2, 3
Scale Factor Temperature Shift (TC= -55 to +125°C) 2
-002 thru -050
Non-Linearity
-100 & -200
(-90 to +90% of Full Scale) 2, 3
-400
Power Supply Rejection Ratio
Output Impedance
Operating Voltage
Operating Current (IDD+IVR) 2
Mass: ‘L’ package (add 0.06 grams for ‘J’ package)
Note 2: Tighter tolerances available on special order.
TYP
MAX
UNITS
2
2
1
100
50
1
3
4
2
300
200
2
250
0.5
1.0
2.0
%
-250
% of span
(ppm of span)/°C
%
ppm/°C
0.3
0.5
% of span
1.0
25
dB
90
Ohms
4.75
5.0
5.25
Volts
8
10
mA
0.62
grams
Note 3: 100g and greater versions are tested from -65 to +65g.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 2]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
Model 1221 Low Noise Analog Accelerometer
$%62/87(0$;,0805$7,1*6 *
Case Operating Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55 to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55 to +125°C
Acceleration Over-range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000g for 0.1 ms
Voltage on VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to 6.5V
Voltage on Any Pin (except DV) to GND 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to VDD+0.5V
Voltage on DV to GND 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±15V
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mW
Note 4: Voltages on pins other than DV, GND or VDD may exceed 0.5 volt above or below the supply voltages provided the current is limited to 1 mA..
Note 5: The application of DV voltages higher than required to bring the output to positive full scale may cause device damage.
* NOTICE: Stresses greater than those listed above may cause permanent damage to the device. These are stress ratings only.
Functional operation of the device at or above these conditions is not implied. Exposure to absolute maximum rating conditions
for extended periods may affect device reliability.
PINOUT
RECOMMENDED CONNECTIONS
(LCC & JLCC PACKAGES)
The 2.5V reference input (pin 17) may be driven from either a precision voltage source by the capacitively bypassed
resistive divider shown above.
DEFLECTION VOLTAGE (DV) TEST INPUT: This test input applies an electrostatic force to the sense element,
simulating a positive acceleration. It has a nominal input impedance of 32 k6 and a nominal open circuit voltage of
½ VDD. For best accuracy during normal operation, this input should be left unconnected or connected to a voltage
source equal to ½ of the VDD supply. The change in differential output voltage (AOP - AON) is proportional to the
square of the difference between the voltage applied to the DV input (VDV) and ½ VDD. Only positive shifts in the
output voltage may be generated by applying voltage to the DV input. When voltage is applied to the DV input, it
should be applied gradually. The application of DV voltages greater than required to bring the output to positive full
scale may cause device damage. The proportionality constant (k) varies for each device and is not characterized.
∆ ( A O P − A O N ) ≈ k (V D V − 21 V D D )
2
ESD and LATCH-UP CONSIDERATIONS: The model 1221 accelerometer is a CMOS device subject to damage
from large electrostatic discharges. Diode protection is provided on the inputs and outputs but care should be
exercised during handling to assure that the device is placed only on a grounded conductive surface. Individuals and
tools should be grounded before coming in contact with the device. Do not insert the model 1221 into (or remove it
from) a powered socket.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 3]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
Model 1221 Low Noise Analog Accelerometer
%,$667$%,/,7<&216,'(5$7,216
Bias temperature hysteresis can be minimized by temperature cycling your model 1221 accelerometer after it has
been soldered to your circuit board. If possible, the assembled device should be exposed to ten cycles from -40 to
+85°C minimum (-55 to +125°C recommended). The orientation to the Earth's gravitational field during temperature
cycling should preferrably be in the same orientation as it will be in the final application. The accelerometer does not
need to have power applied during this temperature cycling.
3$&.$*(',0(16,216
DIM
A
B
C
D
E
F
G
H
J
K
L
*M
N
P
R
S
*T
*U
NOTES:
1. *
2.
3.
4.
5.
INCHES
MILLIMETERS
MIN
MAX
MIN
MAX
0.342 0.358
8.69
9.09
0.346 0.378
8.79
9.60
0.050 0.060
1.27
1.52
0.095 0.115
2.41
2.92
0.075 0.095
1.91
2.41
0.050 BSC
1.27 BSC
0.022 0.028
0.56
0.71
0.050 TYP
1.27 TYP
0.004 x 45°
0.10 x 45°
0.010 R TYP
0.25 R TYP
0.016 TYP
0.41 TYP
0.048 TYP
1.23 TYP
.050
.070
1.27
1.78
.012
.020
0.30
0.51
0.03 R TYP
0.76 R TYP
45° MINIMUM
0.085 TYP
2.16 TYP
0.175 TYP
4.45 TYP
DIMENSIONS 'M', 'T' & 'U' LOCATE ACCELERATION SENSING ELEMENT’S CENTER OF MASS .
LID IS ELECTRICALLY TIED TO TERMINAL 19 (GND).
CONTROLLING DIMENSION: INCH.
TERMINALS PLATED 60 MICRO-INCHES MIN GOLD OVER 80 MICRO-INCHES MIN NICKEL.
PACKAGE: 90% MINIMUM ALUMINA (BLACK), LID: SOLDER SEALED KOVAR.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 4]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
Model 1221 Low Noise Analog Accelerometer
,17(51$/7(03(5$785(6(16,1*
The model 1221 accelerometer contains a temperature
dependent current source that is output on pin 8. This signal is
useful for measuring the internal temperature of the
accelerometer so that any previously characterized bias and
scale factor temperature dependence, for a particular
accelerometer, can be corrected. The nominal output current
at 25°C is 500 A and the nominal sensitivity is 1.5 A/°C. It
is up to the user to characterize each device’s exact output
current versus temperature over the range it is to be used.
Fluctuations in VDD & VR have little effect on the temperature
reading. A reduction of 0.10 V to both VDD & VR will reduce the
current about 1 A which corresponds to less than a 1°C
change in reading.
With a single resistor RT = 2K between IT (pin 8) and GND, as shown in Figure 1, the output voltage VT will vary between
+0.76 and +1.3 volts from -55 to +125°C, which equates to a sensitivity of +3 mV/°C.
[
[
V T ≈ R T (5 0 0 µ A ) + (1.5 µA )(T − 2 5 )
]]
∆V T
= R T (1.5 µ A )
∆T
If a greater voltage change versus temperature or
a lower signal source impedance is needed, the
circuit in Figure 2 can be used. With VOFF = -5V,
gain resistor RG = 15.0K and offset resistor ROFF =
7.32K, the output voltage VT will vary between +4.5
and +0.5 Volts from -55 to +125°C, which equates
to a sensitivity of -29 mV/°C.
V OFF
+ (5 00 µA ) + (1.5 µ A )( T − 2 5 )
VT ≈ −RG
R OFF
[
R OFF =
]
− V OFF
[
]
V T
(
)
R G + (5 0 0 µA ) + (1.5 µA ) T − 2 5
RG =
− ∆V T
(1.5 µA )( ∆ T )
∆V T
= − R G (1.5 µA )
∆T
Figure 3 shows the voltage compliance of the
temperature dependent current source (IT) at
room temperature. The voltage at pin 8 must
be kept in the 0 to +3V range in order to
achieve proper temperature readings.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 5]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
Model 1221 Low Noise Analog Accelerometer
62/'(5,1*5(&200(1'$7,216
Reflow using a hotplate is the preferred method for assembling the model 1221 surface mount accelerometer to your
Printed circuit board. Sn62 or Sn63 type solder is recommended. Hand soldering using a fine tipped soldering iron is
possible but difficult without a steady hand and some form of visual magnification due to the small size of the connections.
When using the hand solder iron method, it’s best to purchase the J-Leaded version (1221J) for easier visual inspection
of the finished solder joints.
Pre-Tinning of Accelerometer Leads is Recommended: To prevent gold migration embrittlement of the solder joints,
it is best to pre-tin the accelerometer leads. The solder bath method of pre-tinning is not recommended due to the high
degree of heat the interior of the device gets subjected to which may cause permanent shifts in the bias and scale factor.
Instead, we recommend tinning one lead at a time, to prevent excessive heating of the accelerometer, using a fine-tipped
solder iron and solder wire.
Hotplate Attach Method using Solder Paste or Solder Wire: Apply solder to the circuit board’s pads using Sn62 or Sn63
solder paste or pre-tin the pads using solder and a fine tipped soldering iron. If pre-tinning with an iron, apply flux to the
tinned pads prior to placing the components. Place the accelerometer in its proper position onto the pasted or tinned pads
then place the entire assembly onto a hotplate that has been pre-heated to 200°C. Leave on hotplate only long enough
for the solder to flow on all pads (DO NOT OVERHEAT!)
Solder Iron Attach Method using Solder Paste: Apply solder paste to the circuit board’s pads where the accelerometer
will be attached. Place the accelerometer in its proper position onto the pasted pads. Press gently on the top of the
accelerometer with an appropriate tool to keep it from moving and heat one of the corner pads, then an opposite corner
pad with the soldering iron. Make sure the accelerometer is positioned so all 20 of its connections are centered on the
board’s pads. Once the two opposite corner pads are soldered, the part is secure to the board and you can work your way
around soldering the remaining 18 connections. Allow the accelerometer to cool in between soldering each pin to prevent
overheating.
Solder Iron Attach Method using Solder Wire: Solder pre-tin two opposite corner pads on the circuit board where the
accelerometer will be attached. Place the accelerometer in its proper position onto the board. Press gently on the top of
the accelerometer and heat one of the corner pads that was tinned and the part will drop down through the solder and seat
on the board. Do the same at the opposite corner pad that was tinned. Make sure the accelerometer is positioned so all
20 of its connections are centered on the board’s pads. Once the two opposite corner pads are soldered, the part is secure
to the board and you can work your way around soldering the remaining 18 connections. Allow the accelerometer to cool
in between soldering each pin to prevent overheating.
LCC & JLCC Solder Contact Plating Information: The plating composition and thickness for the solder pads and
castellations on the “L” suffix (LCC) package are 100 to 225 micro-inches thick of gold (Au) over 80 to 350 micro-inches
thick of nickel (Ni) over a minimum of 5 micro-inches thick of moly-manganese or tungsten refractory material. The leads
for the “J” suffix (JLCC) package are made of CDA102 copper (Cu) have the same gold over nickel plating thicknesses
as for the LCC pads.
Recommended Solder Pad Pattern: The recommended solder pad size and shape for both the LCC and J-LCC
packages is shown in the diagram and table below. These dimensions are recommendations only and may or may not
be optimum for your particular soldering process.
DIM
A
B
C
D
E
F
G
inch
.230
.430
.100
.033
.050
.013
.120
mm
5.84
10.92
2.54
0.84
1.27
0.33
3.05
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 6]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05
APPLICATION NOTE
Model 1221 Accelerometer
$'',1*$6,1*/((1'('287387727+(02'(/
',))(5(17,$/287387$&&(/(520(7(5
R1 = R2 = 5.00K ±0.5% for precision 2.50V ref.
C1 = C2 = 0.01 F ceramic
R3, R4, R5 & R6 = 20k6 to 50k6
R3 = R5 to within 0.1% for common mode rejection
R4 = R6 to within 0.1% for common mode rejection
R4 / R3 ratio accurate to within 0.1% for gain control
R6 / R5 ratio accurate to within 0.1% for gain control
To achieve the highest resolution and lowest noise performance from your model 1221 accelerometer module,
it should be connected to your voltage measurement instrument in a differential configuration using both the AOP and AON
output signals. If your measurement instrument lacks differential input capability or you desire to use a differential input
capable instrument in single ended mode, then the circuit above can be used to preserve the low noise performance of
the model 1221 while using a single ended type connection.
This circuit converts the ± 4 Volt differential output of the model 1221 accelerometer, centered at +2.5 Volts, to
a single ended output centered about ground (0.0 Volts). It provides the advantage of low common mode noise by
preventing the ground current of the model 1221 from causing an error in the voltage reading.
The op-amp should be located as close as possible to your voltage monitoring equipment so that the majority of
the signal path is differential. Any noise present along the differential path will affect both wires to the same degree and
the op-amp will reject this noise because it is a common mode signal. The op-amp type is not critical; a A741 or ¼ of a
LM124 can be used. Both plus and minus supplies are needed for the op-amp to accommodate the positive and negative
swings of the single ended output signal.
The gain of the op-amp is determined by the ratio R4/R3 (where R4=R6 and R3=R5). If R3 through R6 are all the
same value, the gain equals 1 and the output swing will be ± 4 Volts single ended with respect to ground. To obtain a ±
5 Volt single ended output, set R4/R3 = R6/R5 = 5/4 = 1.25. The single ended output of the op-amp will be centered at
ground if R4 and C3 are tied to ground; using some other fixed voltage for this reference can shift the output. The value
of the optional capacitors C3 and C4 (C3=C4) can be selected to roll off the frequency response to the frequency range
of interest.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. 1445 NW Mall Street, Issaquah, WA 98027-5344
web site: www.silicondesigns.com
[page 7]
Phone: 425-391-8329
Fax: 425-391-0446
Aug 05