MLX90313 データシートの表示（PDF） - Melexis Microelectronic Systems
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MLX90313 Datasheet PDF : 35 Pages
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MLX90313
Programmable IR Sensor Interface
Analog-to-Digital Converter (ADC)
MLX90313 contains a 12-bit internal analog to digital converter. Real 12 bit conversion is achieved by a
fully differential signal path of the converter. The input amplifier of the ADC has a fixed gain of 3.
Automatic calibration is implemented in the background, which allows precise conversion in a very wide
temperature range. The ADC sampling rate is 7k samples/second. The reference voltage for the ADC is
normally a scaled version of the internal band-gap reference and is fixed to be 2.5V. Alternatively
MLX90313 can be configured to work with an external reference potential applied to the AGND pin. In
this case the appropriate bit in the configuration register (SELADREF bit in Confreg1) must be cleared.
Internal ADC can work with references down to 1 V keeping the 12-bit resolution.
The ADC contains an interface circuit to scale and offset the analog signals in order to make the most
efficient use of the available resolution. After amplification the IR and Temp sensor signals are referred to
AGND voltage level (typical value 2.5V). The additional offset is scaled version of the AGND.
The ADC interface circuit is given below. The output of the Temp-chain is amplified relative to the voltage
reference VrefT, which can be controlled with 2 bits (bit10 and bit9, EEPROM address 02h). The possible
values for VrefT can be calculated according to the equation:
VrefT = VAgnd ×1.4 × (63 + K ) , where K =0 to 3, corresponding to the value of the control bits.
70
The typical values are 3.15, 3.20, 3.25 and 3.3V. If the temp path amplifier is bypassed then VrefT will be
fixed to: Agnd x 0.28 = 0.7V typical.
The output of the IR-chain is amplified relative to Refir and can be calculated according to the following
equation:
Vrefir
=
VAgnd
×1.4 ×
70
(34
+
K
)
,
Where
K=0:31
depending
on
the
selected
value
of
Rsel[4:0]
The typical values (for Agnd=2.5V) are listed in the table below:
ADC interface setting
RSEL[4:0]
Refir [V] RSEL[4:0]
Refir [V] RSEL[4:0]
Refir [V]
11111b
3.25 10111b
2.85 01111b
2.45
11110b
3.20 10110b
2.80 01110b
2.40
11101b
3.15 10101b
2.75 01101b
2.35
11100b
3.10 10100b
2.70 01100b
2.30
11011b
3.05 10011b
2.65 01011b
2.25
11010b
3.00 10010b
2.60 01010b
2.20
11001b
2.95 10001b
2.55 01001b
2.15
11000b
2.90 10000b
2.50 01000b
2.10
RSEL[4:0]
00111b
00110b
00101b
00100b
00011b
00010b
00001b
00000b
Refir [V]
2.05
2.00
1.95
1.90
1.85
1.80
1.75
1.70
MLX90313 Programmable IR sensor Interface Page 11
3901090313
Rev 1.0 21-July-2001
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