19-2088; Rev 1; 10/01
KIT
ATION
EVALU
BLE
AVAILA
Low-Cost Automotive Sensor Signal
Conditioner
General Description
Features
o
Provides Amplification, Calibration, and
Temperature Compensation
o
Selectable Output Clipping Limits
o
Accommodates Sensor Output Sensitivities
from 5mV/V to 40mV/V
o
Single-Pin Digital Programming
o
No External Trim Components Required
o
16-Bit Offset and Span Calibration Resolution
o
Fully Analog Signal Path
o
PRT Bridge Can Be Used for Temperature-
Correction Input
o
On-Chip Lookup Table Supports Multipoint
Calibration Temperature Correction
o
Fast 3.2kHz Frequency Response
o
On-Chip Uncommitted Op Amp
o
Secure-Lock™ Prevents Data Corruption
MAX1455
The MAX1455 is a highly integrated automotive analog-
sensor signal processor for resistive element sensors.
The MAX1455 provides amplification, calibration, and
temperature compensation that enable an overall per-
formance approaching the inherent repeatability of the
sensor. The fully analog signal path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with integrated 16-bit digi-
tal-to-analog converters (DACs). Offset and span are
also calibrated using 16-bit DACs, allowing sensor
products to be truly interchangeable.
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step programmable-gain ampli-
fier (PGA), a 768-byte (6144 bits) internal EEPROM,
four 16-bit DACs, an uncommitted op amp, and an on-
chip temperature sensor. In addition to offset and span
compensation, the MAX1455 provides a unique tem-
perature compensation strategy that was developed to
provide a remarkable degree of flexibility while minimiz-
ing testing costs.
The MAX1455 is available in die form, 16-pin SSOP and
TSSOP packages.
Customization
Maxim can customize the MAX1455 for high-volume
dedicated applications. Using our dedicated cell library
of more than 2000 sensor-specific function blocks,
Maxim can quickly provide a modified MAX1455 solu-
tion. Contact Maxim for further information.
PART
MAX1455EUE*
MAX1455AUE*
MAX1455EAE
MAX1455AAE
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +125°C
-40°C to +85°C
-40°C to +125°C
PIN-PACKAGE
16 TSSOP
16 TSSOP
16 SSOP
16 SSOP
Applications
Pressure Sensors and Transducers
Piezoresistive Silicon Sensors
Strain Gauges
Resistive Element Sensors
Accelerometers
Humidity Sensors
MR and GMR Sensors
MAX1455C/D
-40°C to +85°C
Dice**
*Future
product—contact factory for availability.
**Dice
are tested at T
A
= +25°C, DC parameters only.
Pin Configuration
TOP VIEW
TEST1 1
16 TEST2
15 TEST3
14 TEST4
MAX1455
13 DIO
12 UNLOCK
11 V
DD2
10 AMP-
9
AMPOUT
Outputs
Ratiometric Voltage Output
Programmable Output Clip Limits
OUT 2
INP 3
BDR 4
INM 5
V
SS
6
A detailed Functional Diagram appears at end of data sheet.
Secure-Lock is a trademark of Maxim Integrated Products, Inc.
V
DD1
7
AMP+ 8
SSOP/TSSOP
________________________________________________________________
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.
Low-Cost Automotive Sensor Signal
Conditioner
MAX1455
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
DD_
to V
SS
.......................................-0.3V, +6V
V
DD1
- V
DD2
..............................................................-0.3V, +0.6V
All Other Pins..................................(V
SS
- 0.3V) to (V
DD_
+ 0.3V)
Short-Circuit Duration, OUT, BDR, AMPOUT .............Continuous
Continuous Power Dissipation (T
A
= +70°C)
16-Pin SSOP (derate 8.00mW/°C above +70°C) .........640mW
Operating Temperature Ranges (T
MIN
to T
MAX
)
MAX1455EUE ..................................................-40°C to +85°C
MAX1455AUE ................................................-40°C to +125°C
MAX1455C/D ...................................................-40°C to +85°C
MAX1455EAE ..................................................-40°C to +85°C
MAX1455AAE ................................................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°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.
ELECTRICAL CHARACTERISTICS
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
GENERAL CHARACTERISTICS
Supply Voltage
Supply Current
Oscillator Frequency
ANALOG INPUT
Input Impedance
Input-Referred Adjustable Offset
Range
Input-Referred Offset Tempco
Amplifier Gain Nonlinearity
Common-Mode Rejection Ratio
Minimum Input-Referred FSO
Range
Maximum Input-Referred FSO
Range
ANALOG OUTPUT
Minimum Differential Signal-
Gain Range
Maximum Differential Signal-
Gain Range
PGA [3:0] = 0000
PGA [3:0] = 1111
Clip[1:0] = 00
Clip[1:0] = 01
Clip[1:0] = 10
Clip[1:0] = 11
Load Current Source
Low
High
Low
High
Low
High
Low
High
39
234
0.10
4.90
0.15
4.85
0.20
4.80
0.25
4.75
1
mA
V
V/V
V/V
CMRR
Specified for common-mode voltages
between V
SS
and V
DD
(Note 3)
(Note 3)
R
IN
Offset TC = 0 (Note 2), minimum gain
T
A
= T
MIN
to T
MAX
1
±150
±1
0.025
90
7
40
MΩ
mV
µV/°C
%
dB
mV/V
mV/V
V
DD
I
DD
f
OSC
I
DD1
+ I
DD2
(Note 1)
0.85
4.5
5.0
3.0
1
5.5
6.0
1.15
V
mA
MHz
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Output Clip Voltage Settings
V
OUT
No load,
T
A
= T
MIN
to T
MAX
V
OUT
= +0.5V to +4.5V, T
A
= T
MIN
to T
MAX
,
Clip[1:0] = 00
2
_______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
Load Current Sink
DC Output Impedance
Offset DAC Output Ratio
Offset TC DAC Output Ratio
Step Response
Output Capacitive Load
Output Noise
BRIDGE DRIVE
Bridge Current
Current Mirror Ratio
Minimum FSODAC Code
DIGITAL-TO-ANALOG CONVERTERS
DAC Resolution
ODAC Bit Weight
OTCDAC Bit Weight
FSODAC Bit Weight
FSOTCDAC Bit Weight
COARSE-OFFSET DAC
IRODAC Resolution
IRODAC Bit Weight
INTERNAL RESISTORS
Current-Source Reference
Full-Span Output (FSO) Trim
Resistor
Resistor Temperature Coefficient
Minimum Resistance Value
Maximum Resistance Value
Resistor Matching
AUXILIARY OP AMP
Open-Loop Gain
Input Common-Mode Range
Output Swing
V
CM
No load, T
A
= T
MIN
to T
MAX
V
SS
V
SS
+
0.01
90
V
DD
V
DD
-
0.01
dB
V
V
R
ISRC
∆R
STC
Applies to R
ISRC
and
∆R
STC
Applies to R
ISRC
and
∆R
STC
Applies to R
ISRC
and
∆R
STC
R
ISRC
to
∆R
STC
75
75
1333
60
90
1
kΩ
kΩ
ppm/°C
kΩ
kΩ
%
Excluding sign bit
∆V
OUT
/∆CODE, input referred,
DAC reference = V
DD
= +5.0V (Note 4)
3
9
Bits
mV/Bit
∆
V
OUT
/
∆
CODE, DAC reference = V
DD
=
+5.0V (Note 4)
∆V
OUT
/
∆C
ODE, DAC reference = V
BDR
=
2.5V (Note 4)
∆
V
OUT
/
∆
CODE, DAC reference = V
DD
=
+5.0V (Note 4)
∆V
OUT
/
∆C
ODE, DAC reference = V
BDR
=
2.5V (Note 4)
16
153
76
153
76
Bits
µV/Bit
µV/Bit
µV/Bit
µV/Bit
Recommended minimum value
I
BDR
V
BDR
≤
3.75V
0.1
0.5
12
4000
2
mA
mA/mA
Hex
DC to 1kHz (gain = minimum, source
impedance = 5kΩ)
2.5
∆V
OUT
/∆ODAC
∆V
OUT
/∆OTCDAC
0% to 63% of final value
SYMBOL
CONDITIONS
V
OUT
= +0.5V to +4.5V, T
A
= T
MIN
to T
MAX
,
Clip[1:0] = 00
1
1.0
1.0
300
1000
MIN
TYP
MAX
2
UNITS
mA
Ω
V/V
V/V
µs
nF
mV
RMS
MAX1455
_______________________________________________________________________________________
3
Low-Cost Automotive Sensor Signal
Conditioner
MAX1455
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
PARAMETER
Output Current Drive
Common-Mode Rejection Ratio
Input Offset Voltage
Unity-Gain Bandwidth
TEMPERATURE-TO-DIGITAL CONVERTER
Temperature ADC Resolution
Offset
Gain
Nonlinearity
Lowest Digital Output
Highest Digital Output
EEPROM
Maximum Erase/Write Cycles
Erase Time
(Notes 6, 7)
(Note 8)
7.1
10k
Cycles
ms
8
±3
1.45
±1
00
AF
Bits
Bits
°C/Bit
LSB
Hex
Hex
CMRR
V
OS
SYMBOL
CONDITIONS
V
OUT
= (V
SS
+ 0.25) to (V
DD
- 0.25)
V
CM
= V
SS
to V
DD
V
IN
= 2.5V unity-gain
buffer (Note 5)
T
A
= +25°C
T
A
= T
MIN
to T
MAX
2
MIN
-1
70
±1
±20
±25
TYP
MAX
+1
UNITS
mA
dB
mV
MHz
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Excludes sensor or load current.
This is the maximum allowable sensor offset.
This is the sensor’s sensitivity normalized to its drive voltage, assuming a desired full-span output of 4V and a bridge voltage of 2.5V.
Bit weight is ratiometric to V
DD
.
All units production tested at T
A
= +25°C. Limits over temperature are guaranteed by design.
Programming of the EEPROM at temperatures below +70°C is recommended.
For operation above +70°C, limit erase/write cycle to 100.
All erase commands require 7.1ms minimum time.
Typical Operating Characteristics
(V
DD_
= +5V, V
SS
= 0, T
A
= +25°C, unless otherwise noted.)
OFFSET DAC DNL
MAX1455 toc01
AMPLIFIER GAIN NONLINEARITY
MAX1455 toc02
OUTPUT NOISE
INP - INM SHORTED TOGETHER
PGA = 0HEX
MAX1455 toc03
2.5
2.0
1.5
1.0
DNL (mV)
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
0
10k
20k
30k
40k
50k
60k
5.0
OUTPUT ERROR FROM STRAIGHT LINE (mV)
ODAC = +6000HEX
OTCDAC = 0
FSODAC = 6000HEX
FSOTCDAC = 8000HEX
IRO = 2HEX
PGA = 0
2.5
0
OUT
10mV/div
-2.5
-5.0
70k
-50
-30
-10
10
30
50
400µs/div
DAC CODE
INPUT VOLTAGE [INP - INM] (mV)
4
_______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Pin Description
PIN
1, 15, 16
NAME
TEST1,
TEST3,
TEST2
OUT
INP
BDR
INM
V
SS
V
DD1
AMP+
AMPOUT
AMP-
V
DD2
UNLOCK
DIO
TEST4
FUNCTION
Test Pins. Connect to V
SS
or leave unconnected.
Analog Output. Internal voltage nodes can be accessed in digital mode. OUT can be parallel
connected to DIO. Bypass OUT to ground with a 0.1µF capacitor to reduce output noise.
Positive Input. Can be swapped to INM by the Configuration register.
Bridge Drive Output
Negative Input. Can be swapped to INP by the Configuration register.
Negative Supply Voltage
Positive Supply Voltage 1. Connect a 0.1µF capacitor from V
DD
to V
SS
.
Auxiliary Op Amp Positive Input
Auxiliary Op Amp Output
Auxiliary Op Amp Negative Input
Positive Supply Voltage 2. Connect a 0.47µF capacitor from V
DD2
to V
SS
. Connect V
DD2
to V
DD1
or
for improved noise performance, connect a 1kΩ resistor to V
DD1
.
Secure-Lock Disable. There is a 150µA pulldown to V
SS
. Connect to V
DD
to disable Secure-Lock
and enable serial communication.
Digital Input Output. Single-pin serial communication port. There are no internal pullups on DIO.
Connect pullup resistor from DIO to V
DD
when in digital mode.
Test Pin. Do not connect.
MAX1455
2
3
4
5
6
7
8
9
10
11
12
13
14
Detailed Description
The MAX1455 provides amplification, calibration, and
temperature compensation to enable an overall perfor-
mance approaching the inherent repeatability of the
sensor. The fully analog signal path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with the integrated 16-bit
DACs. The MAX1455 includes four selectable high/low
clipping limits set in discrete 50mV steps from
0.1V/4.9V to 0.25V/4.75V. Offset and span can be cali-
brated to within ±0.02% of span.
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step PGA, a 768-byte (6144 bits)
internal EEPROM, four 16-bit DACs, an uncommitted op
amp, and an on-chip temperature sensor. The MAX1455
also provides a unique temperature compensation strat-
egy that was developed to provide a remarkable degree
of flexibility while minimizing testing costs.
The customer can select from 1 to 114 temperature
points to compensate their sensor. This allows the lati-
tude to compensate a sensor with a simple first-order
linear correction or match an unusual temperature
curve. Programming up to 114 independent 16-bit
EEPROM locations corrects performance in 1.5°C tem-
perature increments over a range of -40°C to +125°C.
For sensors that exhibit a characteristic temperature
performance, a select number of calibration points can
be used with a number of preset values that define the
temperature curve. The sensor and the MAX1455
should be at the same temperature during calibration
and use. This allows the electronics and sensor errors
to be compensated together and optimizes perfor-
mance. For applications where the sensor and elec-
tronics are at different temperatures, the MAX1455 can
use the sensor bridge as an input to correct for temper-
ature errors.
The single pin, serial DIO communication architecture
and the ability to timeshare its activity with the sensor’s
output signal enables output sensing and calibration
programming on a single line by parallel connecting
OUT and DIO. The MAX1455 provides a Secure-Lock
feature that allows the customer to prevent modification
of sensor coefficients and the 52-byte user-definable
EEPROM data after the sensor has been calibrated.
The Secure-Lock feature also provides a hardware
override to enable factory rework and recalibration by
assertion of logic high on the UNLOCK pin.
5
_______________________________________________________________________________________
