MAX1460 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1460

Low-Power, 16-Bit Smart ADC

Maxim Integrated 

MAX1460

Low-Power, 16-Bit Smart ADC

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 coeffi-

cients to calculate the compensated and corrected output.

The MAX1460 supports an automated production envi-

ronment, where a test system communicates with a batch

of MAX1460s and controls temperature and sensor exci-

tation. The three-state digital outputs on the MAX1460

Table 1. Nominal PGA Gain Settings

PGA

SETTING

0

1

2

3

PGA-1

0

0

1

0

PGA-0

0

1

0

1

NOMINAL GAIN

(V/V)

46

61

77

93

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 indi-

vidual 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 coef-

ficients into the MAX1460 nonvolatile EEPROM, and test

the resulting compensation.

The MAX1460 DSP implements the following character-

istic equation:

( ) D= Gain 1+ G1T + G2T 2

( ) Signal + Of0 + Of1T + Of2T 2 + DOFF

where Gain corrects the sensor’s sensitivity, G1 and G2

correct for Gain-TC, T and Signal are the digitized outputs

of the analog front end, Of0 corrects the sensor’s offset,

Of1 and Of2 correct the Offset-TC, and DOFF is 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 impor-

tant 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-

Table 2. Typical Coarse Offset DAC Settings

CO

SETTING

CO-S

CO-1

CO-0

% VDD

(at ADC

input)

-3

1

1

1

-149

-2

1

1

0

-96

-1

1

0

1

-47

-0

1

0

0

5

+0

0

0

0

-5

+1

0

0

1

47

+2

0

1

0

96

+3

0

1

1

149

PGA SETTING

0

(mV RTI)

(VDD = 5V)

-162

-104

-51

5

-5

51

104

162

PGA SETTING

1

(mV RTI)

(VDD = 5V)

-122

-79

-39

4

-4

39

79

122

PGA SETTING

2

(mV RTI)

(VDD = 5V)

-97

-62

-31

3

-3

31

62

97

PGA SETTING

3

(mV RTI)

(VDD = 5V)

-80

-52

-25

3

-3

25

52

80

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