Maxim MAX1460CCM Datasheet

General Description

The MAX1460 implements a revolutionary concept in signal conditioning, where the output of its 16-bit analog-to-digital converter (ADC) is digitally corrected over the specified temperature range. This feature can be readily exploited by automotive, industrial, and medical market segments, in applications such as sensors and smart batteries. Digital correction is provided by an internal digital signal processor (DSP) and on-chip 128bit EEPROM containing user-programmed calibration coefficients. The conditioned output is available as a 12-bit digital word and as a ratiometric (proportional to the supply voltage) analog voltage using an on-board 12-bit digital-to-analog converter (DAC). The uncommitted op amp can be used to filter the analog output, or implement a 2-wire, 4–20mA transmitter.

The analog front end includes a 2-bit programmablegain amplifier (PGA) and a 3-bit coarse-offset (CO) DAC, which condition the sensor’s output. This coarsely corrected signal is digitized by a 16-bit ADC. The DSP uses the digitized sensor signal, the temperature sensor, and correction coefficients stored in the internal EEPROM to produce the conditioned output.

Multiple or batch manufacturing of sensors is supported with a completely digital test interface. Built-in testability features on the MAX1460 result in the integration of three traditional sensor-manufacturing operations into one automated process:

• Pretest: Data acquisition of sensor performance under the control of a host test computer.

• Calibration and Compensation: Computation and storage of calibration and compensation coefficients determined from transducer pretest data.

• Final Test Operation: Verification of transducer calibration and compensation, without removal from the pretest socket.

The MAX1460 evaluation kit (EV kit) allows fast evaluation and prototyping, using a piezoresistive transducer (PRT) and a Windows

-based PC. The user-friendly EV kit simplifies small-volume prototyping; it is not necessary to fully understand the test-system interface, the calibration algorithm, or many other details to evaluate the MAX1460 with a particular sensor. Simply plug the PRT into the EV kit, plug the EV kit into a PC parallel port, connect the sensor to an excitation source (such as a pressure controller), and run the MAX1460 EV kit software. An oven is required for thermal compensation.

Features

♦ Low-Noise, 400µA Single-Chip Sensor Signal

Conditioning

♦ High-Precision Front End Resolves Less than 1µV

of Differential Input Signal

♦ On-Chip DSP and EEPROM Provide Digital

Correction of Sensor Errors

♦ 16-Bit Signal Path Compensates Sensor Offset

and Sensitivity and Associated Temperature Coefficients

♦ 12-Bit Parallel Digital Output

♦ Analog Output

♦ Compensates a Wide Range of Sensor Sensitivity

and Offset

♦ Single-Shot Automated Compensation

Algorithm—No Iteration Required

♦ Built-In Temperature Sensor

♦ Three-State, 5-Wire Serial Interface Supports

High-Volume Manufacturing

________________________Applications

Hand-Held Instruments

Piezoresistive Pressure and Acceleration Transducers and Transmitters

Industrial Pressure Sensors and 4–20mA Transmitters

Smart Battery Charge Systems

Weigh Scales and Strain-Gauge Measurement

Flow Meters

Dive Computers and Liquid-Level Sensing

Hydraulic Systems

Automotive Systems

Customization

Maxim can customize the MAX1460 for unique requirements. With a dedicated cell library of more than 90 sensor-specific functional blocks, Maxim can quickly provide customized MAX1460 solutions, including customized microcode for unusual sensor characteristics. Contact Maxim for further information.

MAX1460

Low-Power, 16-Bit Smart ADC

________________________________________________________________ Maxim Integrated Products 1

19-4784; Rev 0; 10/99

PART

MAX1460CCM 0°C to +70°C

TEMP. RANGE PIN-PACKAGE

48 TQFP

Ordering Information

Functional Diagram appears at end of data sheet.

Pin Configuration appears at end of data sheet.

Windows is a registered trademark of Microsoft Corp.

EVALUATION KIT

AVAILABLE

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.

PGA Gain

MAX1460

Low-Power, 16-Bit Smart ADC

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= +5V, VSS= 0, f

XIN

= 2MHz, TA= T

MIN

to T

MAX

, unless otherwise noted.)

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 ...................................(V

- 0.3V) to (VDD+ 0.3V)

Short-Circuit Duration, All Outputs .............................Continuous

Continuous Power Dissipation (T

= +70°C)

48-Pin TQFP (derate 12.5mW/°C above +70°C ).....1000mW

Operating Temperature Range...............................0°C to +70°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10sec) .............................+300°C

CO-DAC code = 011

CO-DAC code = 010

Continuous conversion

CO-DAC code = 001

CO-DAC code = 000

During operation

CO-DAC code = 100

CO-DAC code = 101

CO-DAC code = 110

CO-DAC code = 111

PGA gain code = 11

PGA gain code = 10

From VSSto V

PGA gain code = 01

PGA gain code = 00

CONDITIONS

134 149 164

81 96 111

32 47 62

-20 -5 10

-10 5 20

-62 -47 -32

-111 -96 -81

% V

-164 -149 -134

Coarse Offset

90 93 96

74 77 80

59 61 64

V/V

43 46 49

µA

400 700

Supply Current (Note 2)

4.75 5.0 5.25

Supply Voltage (Note 1)

CMRRCommon-Mode Rejection Ratio

nV/°C

±1200

Input-Referred Offset TC

Throughput Rate

MΩ

1.0

Input Impedance

ppm/°C

±40

Gain Temperature Coefficient (TC)

UNITSMIN TYP MAXSYMBOLPARAMETER

TA= 0°C to +70°C

5kΩ input impedance

PGA gain code = 00, CO-DAC code = 000

°C

1.3

Linearity

LSB/°C

260

Resolution

LSB

RMS

Output-Referred Noise

RMS

1700

Input-Referred Noise

0.006

INLIntegral Nonlinearity (Note 5)

Bits

Resolution

ADC (Notes 3, 4)

TEMPERATURE SENSOR (Note 6)

GENERAL CHARACTERISTICS

ANALOG INPUT

PGA AND COARSE-OFFSET DAC (Notes 3, 4)

PGA Gain

MAX1460

Low-Power, 16-Bit Smart ADC

_______________________________________________________________________________________ 3

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

DAC Resolution

bits

Integral Nonlinearity INL

LSB

Differential Nonlinearity DNL

0.5

LSB

Op Amp Supply Current 100 µA

Input Common-Mode Range CMR

VSS+ 1.3 VDD- 1.0

Open-Loop Gain A

60 dB

Offset Voltage (as unity-gain follower)

= 2.5V (no load)

-30 +30

Output Voltage Swing No load

VSS+ 0.05 VDD- 0.05

Output Current Range V

OUT

= (VSS+ 0.2V) to (VDD- 0.2V) ±500 µA

Note 1: EEPROM programming requires a minimum VDD= 4.75V. IDDmay exceed its limits during this time. Note 2: This value does not include the sensor or load current. This value does include the uncommitted op amp current. Note that

the MAX1460 will convert continuously if REPEAT MODE is set in the EEPROM.

Note 3: See the Analog Front-End, including PGA, Coarse Offset DAC, ADC, and Temperature Sensor sections. Note 4: The signal input to the ADC is the output of the PGA plus the output of the CO-DAC. The reference to the ADC is V

. The

plus full-scale input to the ADC is +V

and the minus full-scale input to the ADC is -VDD. This specification shows the con-

tribution of the CO-DAC to the ADC input.

Note 5: See Figure 2 for ADC outputs between +0.8500 to -0.8500. Note 6: The sensor and the MAX1460 must always be at the same temperature during calibration and use. Note 7: The Output DAC is specified using the external lowpass filter (Figure 8). Note 8: SDIO is an input/output digital pin. It is only enabled as a digital output pin when the MAX1460 receives from the test sys-

tem the commands 8 hex or A hex (Table 4).

Note 9: XIN is a digital input pin only when the TEST pin is high. Note 10: Guaranteed by design. Not subject to production testing.

ELECTRICAL CHARACTERISTICS (continued)

(VDD= +5V, VSS= 0, f

XIN

= 2MHz, TA= T

MIN

to T

MAX

, unless otherwise noted.)

Input High Voltage V

4.0

Input Low Voltage V

1.0

Input Hysteresis V

HYST

1.0

Input Leakage I

VIN= 0 or V

±10

µA

Input Capacitance C

(Note 10)

50.0

Output Voltage Low V

SINK

= 500µA

0.5

Output Voltage High V

SOURCE

= 500µA

4.5

Three-State Leakage Current I

CS = 0

±10

µA

Three-State Output Capacitance C

OUT

CS = 0 (Note 10)

50.0

Output Voltage Low V

SINK

= 500µA

0.3

Output Voltage High V

SOURCE

= 500µA

4.7

Three-State Leakage Current I

CS = 0

±10

µA

Three-State Output Capacitance C

OUT

CS = 0 (Note 10)

50.0

OUTPUT DAC (Note 7)

UNCOMMITTED OP AMP

DIGITAL INPUTS: START, CS1, CS2, SDIO (Note 8), RESET, XIN (Note 9), TEST

DIGITAL OUTPUTS: D[11...0]

DIGITAL OUTPUTS: SDIO (Note 8), SDO, EOC, OUT

MAX1460

Low-Power, 16-Bit Smart ADC

4 _______________________________________________________________________________________

NAME FUNCTION

1, 2, 12, 13, 18, 19, 31, 32, 36,

41–45

N.C. No Connection. Not internally connected.

3 AGND Analog Ground. Connect to VDDand VSSusing 10kΩ resistors (see Functional Diagram).

4 START

Optional conversion start input signal, used for extending sensor warm-up time. Internally pulled to VDDwith a 1MΩ (typical) resistor.

5 I.C. Internally Connected. Leave unconnected.

9 D9 Parallel Digital Output - bit 9

8 D8 Parallel Digital Output - bit 8

7 D7 Parallel Digital Output - bit 7

6 D6 Parallel Digital Output - bit 6

16, 17

CS1,

CS2

Chip-Select Input. The MAX1460 is selected when CS1 and CS2 are both high. When either CS1 or CS2 is low, all digital outputs are high impedance and all digital inputs are ignored. CS1 and CS2 are internally pulled high to V

with a 1MΩ (typical) resistor.

15 V

Negative Supply Input

14, 37, 38 V

Positive Supply Voltage Input. Connect a 0.1µF bypass capacitor from VDDto VSS. Pins 14, 37, and 38 must all be connected to the positive power supply on the PCB.

11 D11 Parallel Digital Output - bit 11 (MSB)

10 D10 Parallel Digital Output - bit 10

20 SDIO

Serial Data Input/Output. Used only during programming/testing, when the TEST pin is high. The test system sends commands to the MAX1460 through SDIO. The MAX1460 returns the current instruction ROM address and data being executed by the DSP to the test system. SDIO is internally pulled to V

with a 1MΩ (typical) resistor. SDIO goes high impedance when either CS1 or CS2 is low and remains in this state until the test system initiates conversion.

21 SDO

Serial Data Output. Used only during programming/testing. SDO allows the test system to monitor the DSP registers. The MAX1460 returns to the test system results of the DSP current instruction. SDO is high impedance when TEST is low.

RESET

Reset Input. When TEST is high, a low-to-high transition on RESET enables the MAX1460 to accept commands from the test system. This input is ignored when TEST is low. Internally pulled high to V

with a 1MΩ (typical) resistor.

26 D2 Parallel Digital Output - bit 2

25 D1 Parallel Digital Output - bit 1

24 D0 Parallel Digital Output - bit 0 (LSB)

23 EOC

End of Conversion Output. A high-to-low transition of the EOC pulse can be used to latch the Parallel Digital Output (pins D[11...0]).

Pin Description

MAX1460

Low-Power, 16-Bit Smart ADC

_______________________________________________________________________________________ 5

Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.

Pin Description (continued)

NAME FUNCTIONPIN

33 AMPOUT General-Purpose Operational Amplifier Output

30 OUT

Output DAC. The bitstream on OUT, when externally filtered, creates a ratiometric analog output voltage. OUT is proportional to the 12-bit parallel digital output.

29 D5 Parallel Digital Output - bit 5

28 D4 Parallel Digital Output - bit 4

27 D3 Parallel Digital Output - bit 3

34 AMP+ Noninverting Input of General-Purpose Operational Amplifier

35 AMP- Inverting Input of General-Purpose Operational Amplifier

39 XOUT

Internal Oscillator Output. Connect a 2MHz ceramic resonator (Murata CST200) or crystal from XOUT to XIN.

40 XIN

Internal Oscillator Input. When TEST is high, this pin must be driven by the test system with a 2MHz, 50% duty cycle clock signal. The resonator does not need to be disconnected in test mode.

46 INP Positive Sensor Input. Input impedance is typically > 1MΩ. Rail-to-Rail®input range.

47 TEST

Test/Program Mode Enable Input. When high, enables the MAX1460 programming/testing operations. Internally pulled to VSSwith a 1MΩ (typical) resistor.

48 INM Negative Sensor Input. Input impedance is typically > 1MΩ. Rail-to-rail input range.

MAX1460

Low-Power, 16-Bit Smart ADC

6 _______________________________________________________________________________________

Detailed Description

The main functions of the MAX1460 include:

• Analog Front End: Includes PGA, coarse-offset DAC, ADC, and temperature sensor

• Test System Interface: Writes calibration coefficients to the DSP registers and EEPROM

• Test System Interface: observes the DSP operation.

The sensor signal enters the MAX1460 and is adjusted for coarse gain and offset by the analog front end. Five bits in the configuration register set the coarse-offset DAC and the coarse gain of the PGA (Tables 1 and 2). These bits must be properly configured for the optimum dynamic range of the ADC. The digitized sensor signal is stored in a read-only DSP register.

The on-chip temperature sensor also has a 3-bit coarse-offset DAC that places the temperature signal in the ADC operating range. Digitized temperature is also stored in a read-only DSP register. The DSP uses the digitized sensor, the temperature signals, and the correction coefficients to calculate the compensated and corrected output.

The MAX1460 supports an automated production environment, where a test system communicates with a batch of MAX1460s and controls temperature and sen-

sor excitation. The three-state digital outputs on the MAX1460 allow parallel connection of transducers, so that all five serial interface lines (XIN, TEST, RESET, SDIO, and SDO) can be shared. The test system selects an individual transducer using CS1 and CS2. The test system must vary the sensor’s input and temperature, calculate the correction coefficients for each unit, load the coefficients into the MAX1460 nonvolatile EEPROM, and test the resulting compensation.

The MAX1460 DSP implements the following characteristic equation:

where Gain corrects the sensor’s sensitivity, G

and G

correct for Gain-TC, T and Signal are the digitized outputs of the analog front end, Of0corrects the sensor’s offset, Of1and Of2correct the Offset-TC, and D

OFF

the output offset pedestal.

The test system can write the calibration coefficients into the MAX1460 EEPROM or write to the DSP registers directly. The MAX1460 can begin a conversion using either the EEPROM contents or the register contents. When the test system issues commands, the MAX1460 is a serially controlled slave device.

The test system observes the MAX1460 DSP operation in order to acquire the temperature and signal ADC results, to verify the calibration coefficients, and to get the output D. The MAX1460 places the contents of several important DSP registers on the serial interface after the tester issues a Start Conversion command.

After calibration, compensation, and final test, the MAX1460 is adapted to its sensor and the pair can be removed from the test system. Use the resulting trans-

93113

77012

61101

46000

NOMINAL GAIN

(V/V)

PGA-0PGA-1

PGA SETTING

(mV RTI)

= 5V)

CO-0CO-1CO-S

PGA SETTING

(mV RTI)

= 5V)

PGA SETTING

(mV RTI)

= 5V)

PGA SETTING

(mV RTI)

= 5V)

% V

(at ADC

input)

SETTING

122

8097162110+3 149

010+2 52

100+1

6210496

25315147

-4

-39

-79

-122

-3-3-5-5

3355

-25-31-47

-52-62

-104

-96

-80-97-162-149

000+0

001-0

101-1

011-2

111-3

Table 2. Typical Coarse Offset DAC Settings

Table 1. Nominal PGA Gain Settings

PGA

SETTING

-51

D Gain 1 G T G T

=++

()



Signal Of Of T Of T D



++ +

01 22OFF





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