Maxim MAX1450EAP, MAX1450CAP, MAX1450C-D Datasheet
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General Description
The MAX1450 sensor signal conditioner is optimized for
piezoresistive sensor calibration and temperature compensation. It includes an adjustable current source for
sensor excitation and a 3-bit programmable-gain amplifier (PGA). Achieving a total typical error factor within
1% of the sensor’s inherent repeatability errors, the
MAX1450 compensates offset, full-span output (FSO), offset tempco, FSO tempco, and FSO nonlinearity of silicon
piezoresistive sensors via external trimmable resistors,
potentiometers, or digital-to-analog converters (DACs).
The MAX1450 is capable of compensating sensors that
display close error distributions with a single temperature point, making it ideal for low-cost, medium-accuracy
applications. Although optimized for use with popular
piezoresistive sensors, it may also be used with other
resistive sensor types such as strain gauges.
Customization
Maxim can customize the MAX1450 for unique requirements including improved power specifications. With a
dedicated cell library consisting of more than 90 sensor-specific functional blocks, Maxim can quickly provide customized MAX1450 solutions. Contact the
factory for additional information.
Applications
Piezoresistive Pressure and Acceleration
Transducers and Transmitters
Manifold Absolute Pressure (MAP) Sensors
Automotive Systems
Hydraulic Systems
Industrial Pressure Sensors
Features
♦ 1% Sensor Signal Conditioning
♦ Corrects Sensor Errors Using Coefficients Stored
in External Trimmable Resistors, Potentiometers,
or DACs
♦ Compensates Offset, Offset TC, FSO, FSO TC,
and FSO Linearity
♦ Rail-to-Rail
®
Analog Output
♦ Programmable Current Source for Sensor
Excitation
♦ Fast Signal-Path Settling Time (< 1ms)
♦ Accepts Sensor Outputs from 10mV/V to 30mV/V
♦ Fully Analog Signal Path
MAX1450
Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
________________________________________________________________
Maxim Integrated Products
1
PGA
A = 1
OUT
ISRC
BDRIVE
INP
INM
SOTC
SOFF
OFFTC
OFFSET
BBUF
A2
FSOTRIM
A1
A0
+
-
V
DD
V
SS
CURRENT
SOURCE
V
DD
MAX1450
Pin Configuration
19-1365; Rev 0; 5/98
PART
MAX1450CAP
MAX1450C/D
MAX1450EAP -40°C to +85°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
20 SSOP
Dice*
20 SSOP
*
Dice are tested at TA = +25°C, DC parameters only.
Functional Diagram
Ordering Information
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
TOP VIEW
INP
I.C.
I.C.
SOFF
A1
A0
OFFSET
20
INM
19
V
SS
18
BDRIVE
17
ISRCSOTC
16
I.C.
15
V
DD
OUT
14
A2OFFTC
13
12
I.C.
11
FSOTRIMBBUF
1
2
3
4
MAX1450
5
6
7
8
9
10
SSOP
MAX1450
Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= +5V, VSS= 0, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
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.
Supply Voltage, VDDto VSS......................................-0.3V to +6V
All Other Pins ...................................(VSS- 0.3V) to (VDD+ 0.3V)
Short-Circuit Duration, OUT, BBUF, BDRIVE.............Continuous
Continuous Power Dissipation (TA= +70°C)
SSOP (derate 8.00mW/°C above +70°C) ....................640mW
Operating Temperature Range
MAX1450CAP .....................................................0°C to +70°C
MAX1450EAP ..................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10sec).............................+300°C
TA= +25°C (Note 1)
DC to 10Hz, gain = 39,
sensor impedance = 5kΩ
V
OUT
= (VSS+ 0.25V) to (VDD- 0.25V)
,
TA= +25°C
(Note 5)
(Note 4)
5kΩ load to VSSor V
DD,
TA= +25°C
From VSSto V
DD
63% of final value
(Notes 2, 3)
Eight selectable gains (Table 3)
CONDITIONS
µV
RMS
500Output Noise
mA
-1.0 1.0
(sink) (source)
Output Current Range
V
V
SS +
V
DD -
0.25 0.25
Output Voltage Swing
V/V36 39 44
Minimum Differential Signal
Gain
V/V39 to 221Differential Signal Range Gain
mA2.8 3.5I
DD
Supply Current
mV/V10 to 30
Input-Referred Adjustable
Full-Span Output Range
mV±100
Input-Referred Adjustable Offset
Range
dB90CMRRCommon-Mode Rejection Ratio
ms1Output Step-Response Time
MΩ1.0R
IN
Input Impedance
µV/°C±0.5
Input-Referred Offset
Temperature Coefficient
%V
DD
0.01Amplifier Gain Nonlinearity
UNITSMIN TYP MAXSYMBOLPARAMETER
No load, TA= T
MIN
to T
MAX
V
SS +
V
DD -
0.05 0.05
V4.5 5.0 5.5V
DD
Supply Voltage
At any gain ppm/°C±50
Differential Signal Path
Temperature Coefficient
V/V1.15Offset TC Gain
V/V1.15Offset Gain
∆∆V
V
OUT
OFFSET
∆∆V
V
OUT
OFFTC
GENERAL CHARACTERISTICS
ANALOG OUTPUT (PGA)
ANALOG INPUT (PGA)
SUMMING JUNCTION (Figure 1)
MAX1450
Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= +5V, VSS= 0, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.)
Note 1: Contact factory for high-volume applications requiring less than 1.5mA.
Note 2: All electronics temperature errors are compensated together with the sensor errors.
Note 3: The sensor and the MAX1450 must always be at the same temperature during calibration and use.
Note 4: This is the maximum allowable sensor offset at minimum gain (39V/V).
Note 5: This is the sensor’s sensitivity normalized to its drive voltage, assuming a desired full-span output (FSO) of 4V and a bridge
voltage of 2.5V. Operating at lower bridge excitation voltages can accommodate higher sensitivities.
V
BDRIVE
= 2.5V
No load
(V
BDRIVE
- V
BBUF
) at V
BDRIVE
= 2.5V, no load
CONDITIONS
µA-100 100Current Drive
V
V
SS +
V
DD -
1.3 1.3
Voltage Swing
mV-20 20V
OFS
Offset Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
∆I
BDRIVE/
∆I
ISRC
(Figure 2)
V
V
SS +
V
DD -
1.3 1.3
V
BDRIVE
Bridge Voltage Swing
mA0.1 0.5 2.0I
BDRIVE
Bridge Current Range
µA/µA13AACurrent-Source Gain
V
V
SS +
V
DD-
1.3 1.3
V
ISRC
Current-Source Input Voltage
Range
BUFFER (BBUF)
CURRENT SOURCE
______________ Detailed Description
Analog Signal Path
The MAX1450’s signal path is fully differential and combines the following three stages: a 3-bit PGA with
selectable gains of 39, 65, 91, 117, 143, 169, 195, and
221; a summing junction; and a differential to singleended output buffer (Figure 1).
Programmable-Gain Amplifier
The analog signal is first fed into a programmable-gain
instrumentation amplifier with a CMRR of 90dB and a
common-mode input range from VSSto VDD. Pins A0,
A1, and A2 set the PGA gain anywhere from 39V/V to
221V/V (in steps of 26).
MAX1450
Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
4 _______________________________________________________________________________________
NAME FUNCTION
1 INP Positive Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
PIN
2, 3,
12, 16
I.C. Internally connected. Leave unconnected.
4 SOTC
Offset TC Sign Bit Input. A logic low inverts V
OFFTC
with respect to V
SS.
This pin is internally pulled to V
SS
via a 1MΩ (typical) resistor. Connect to VDDto add V
OFFTC
to the PGA output, or leave unconnected (or
connect to VSS) to subtract V
OFFTC
from the PGA output.
8 OFFTC
Offset TC Adjust. Analog input summed with PGA output and V
OFFSET
. Input impedance is typically 1MΩ.
Rail-to-rail input range.
7 A0
PGA Gain-Set LSB Input. Internally pulled to VSSvia a 1MΩ (typical) resistor. Connect to VDDfor a logic
high or VSSfor a logic low.
6 A1
PGA Gain-Set Input. Internally pulled to VSSvia a 1MΩ (typical) resistor. Connect to VDDfor a logic high or
VSSfor a logic low.
5 SOFF
Offset Sign Bit Input. A logic low inverts V
OFFSET
with respect to VSS. This pin is internally pulled to VSSvia
a 1MΩ (typical) resistor. Connect to VDDto add V
OFFSET
to the PGA output, or leave unconnected (or con-
nect to VSS) to subtract V
OFFSET
from the PGA output.
14 OUT PGA Output Voltage. Connect a 0.1µF capacitor from OUT to VSS.
13 A2
PGA Gain-Set MSB Input. Internally pulled to VSSvia a 11kΩ (typical) resistor. Connect to VDDfor a logic
high or VSSfor a logic low.
11 FSOTRIM Bridge Drive Current-Set Input. The voltage on this pin sets the nominal I
ISRC
. See the
Bridge Drive
section.
10 BBUF
Buffered Bridge-Voltage Output (the voltage at BDRIVE). Use with correction resistor R
STC
to correct for FSO
tempco.
9 OFFSET
Offset Adjust Input. Analog input summed with PGA output and V
OFFTC
. Input impedance is typically
1MΩ. Rail-to-rail input range.
Pin Description
15 V
DD
Positive Supply Voltage Input. Connect a 0.1µF capacitor from VDDto VSS.
20 INM Negative Sensor Input. Input impedance is typically 1MΩ. Rail-to-rail input range.
19 V
SS
Negative Power-Supply Input.
18 BDRIVE Sensor Excitation Current Output. This pin drives a nominal 0.5mA through the bridge.
17 ISRC Current-Source Reference. Connect a 50kΩ (typical) resistor from ISRC to VSS.
Figure 1. Signal-Path Functional Diagram
INP
INM
A2
A1 A0
PGA
OFFTC SOTC
±
Σ
±
OFFSET SOFF
A = 1
OUT
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