MAX1460 Datasheet, PDF (6/20 Pages) Maxim Integrated Products – Low-Power, 16-Bit Smart ADC

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 cor-
rection coefficients 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 sen-
Table 1. Nominal PGA Gain Settings
PGA
SETTING
0
1
2
3
PGA-1
0
0
1
1
PGA-0
0
1
0
1
NOMINAL GAIN
(V/V)
46
61
77
93
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 tem-
perature, 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 character-
istic equation:
( ) ^{D = Gain 1 + G}₁^{T + G}₂ ^T2


Signal
+
Of₀
+
Of₁T
+
Of₂
T
2


+ D_OFF
where Gain corrects the sensor’s sensitivity, G₁ and G₂
correct for Gain-TC, T and Signal are the digitized out-
puts of the analog front end, Of0 corrects the sensor’s
offset, Of₁ and Of₂ correct the Offset-TC, and D_OFF is
the output offset pedestal.
The test system can write the calibration coefficients
into the MAX1460 EEPROM or write to the DSP regis-
ters directly. The MAX1460 can begin a conversion
using either the EEPROM contents or the register con-
tents. 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 sev-
eral 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-
Table 2. Typical Coarse Offset DAC Settings
CO
SETTING
CO-S
-3
1
-2
1
-1
1
-0
1
+0
0
+1
0
+2
0
+3
0
CO-1
1
1
0
0
0
0
1
1
CO-0
1
0
1
0
0
1
0
1
% V_DD
(at ADC
input)
-149
-96
-47
5
-5
47
96
149
PGA SETTING
0
(mV RTI)
(V_DD = 5V)
-162
-104
-51
5
-5
51
104
162
PGA SETTING
1
(mV RTI)
(V_DD = 5V)
-122
-79
-39
4
-4
39
79
122
PGA SETTING
2
(mV RTI)
(V_DD = 5V)
-97
-62
-31
3
-3
31
62
97
PGA SETTING
3
(mV RTI)
(V_DD = 5V)
-80
-52
-25
3
-3
25
52
80
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