MAX1460 Datasheet, PDF (14/20 Pages) Maxim Integrated Products – Low-Power, 16-Bit Smart ADC

Low-Power, 16-Bit Smart ADC
Table 9. MAX1460 Conversion Timing
PARAMETER
Sensor Warm-Up Time
ADC Time
DSP Time
EOC Pulse Width
Conversion Time
SYMBOL
t_WARM
t_ADC
t_DSP
t_EOC
t_CONV
MIN
35
130,585
3,220
8
133,805
MAX
—
130,585
3,364
8
133,949
UNITS
ms
XIN clk cycles
XIN clk cycles
XIN clk cycles
XIN clk cycles
Applications Information
Calibration and Compensation Procedure
Perform fine calibration by characterizing the sensor/
MAX1460 pair using the test system and then finding
the calibration coefficients Gain, G₁, G₂, Of₀, Of₁, and
Of₂ using the equations below. This simple fine-calibra-
tion procedure requires three temperatures, denoted A,
B, and C, and two sensor excitations, named S and L
for small and large. Thus, there are six data points (AS,
AL, BS, BL, CS, and CL); six unknown calibration coeffi-
cients; and six versions of the characteristic equation, in
the form:
The A_L and A_S versions of equation 1 may be ratioed to
obtain:
Equation (2a)
⋅ Signal_AL − x
Signal_AS
+ Of₀ +
Of₁T_A
2
+ Of₂T_A
=0
1− x
Similarly,
Equation (2b)
⋅ Signal_BL − x
Signal_BS
+ Of₀
+
Of₁T_B
2
+ Of₂T_B
=0
1− x
Equation (1)
D_L
−
D_OFF
=
Gain
₁₊
G₁T_C
+
G₂
T_C2




Signal_CL
+
Of₀
+
Of₁T_C
+
Of₂
T_C2


where D_L, D_S, and D_OFF are determined by the end
product specification. D_L is the desired MAX1460 out-
put corresponding to the L sensor excitation; D_S is the
desired MAX1460 output corresponding to the S sen-
sor excitation; D_OFF is the desired midscale output;
Signal_CL is the digitized sensor reading at temperature
C with the L sensor excitation applied; and T_C is the
digitized temperature reading at temperature C.
Unstable digitized temperature readings indicate that
thermal equilibrium has not been achieved, necessitat-
ing increased soak times or a better thermal control.
Averaging many readings from the MAX1460 will help
filter out AC variations in the sensor excitation and oven
temperature.
Begin calibration by soaking the sensor and the
MAX1460 pair at the first temperature, A, and apply the
L excitation to the sensor. Start a conversion and
record the digitized temperature T_A and the digitized
signal Signal_AL. Apply the S sensor excitation, and
record the digitized signal Signal_AS. Repeat this proce-
dure for temperatures B and C, recording T_B, Signal_BL,
Signal_BS, T_C, Signal_CL, and Signal_CS.
Equation (2c)
⋅ Signal_CL − x
Signal_CS
+ Of₀
+
Of₁T_C
2
+ Of₂T_C
=0
1− x
where
Equation (3)
x = ^{DL − DOFF}
D_S − D_OFF
Equations 2a, 2b, and 2c form a system of three linear
equations, with three unknowns, Of₀, Of₁, and Of₂.
Solve for Of₀, Of₁, and Of₂.
The small sensor excitation versions of Equation 1 can
be ratioed to obtain:
Equation (4a)
(Y_CS − Y_AS ) + G₁ (T_A Y_CS − T_CY_AS ) +
G₂


T_A
2
Y_CS
−
T_C2
Y_AS


=
0
Equation (4b)
(Y_CS − Y_BS ) + G₁ (T_B Y_CS − T_CY_BS ) +
G₂


T_B2
Y_CS
−
T_C2
Y_BS


=0
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