Rainbow-electronics MAX1329 Uživatelský manuál stáhnout pdf (Strana 65)

MAX1329/MAX1330

12-/16-Bit DASs with ADC, DACs, DPIOs, APIOs,

Reference, Voltage Monitors, and Temp Sensor

______________________________________________________________________________________ 65

Optical Reflectometry Application with

Dual LED and Single Photodiode

Figure 28 illustrates the MAX1329 in an optical reflectom-

etry application with two transmitting LEDs and one

receiving photodiode. The LEDs transmit light at specific

frequencies onto the sample strip and the photodiode

receives the reflections from the strip. Set the DACA out-

put to provide the appropriate bias currents for the LEDs.

The DSWA and DSWB switches are open in this configu-

ration. The LED bias current is calculated as I

LED

OUTA

. REFADC is used as an analog ground and

DACB is set to ensure that the photodiode is not forward

biased. The I

current is converted to a voltage through

the R

resistor and measured by the internal ADC.

SPDT1 and SPDT2 are configured as single-pole

double-throw switches and enable switching between

BAT

PHOTO

DIODE

DACA

OUTA

FBA

DACB

OUTB

FBB

SNO1

SNC1

SCM1

REFADC

REFDAC

REFADJ2.5V

REF

= 0.5, 0.82, 1

REFDAC

SNC2

SNO2

SCM2

BAT

LED

1.25V

2.50V

= 0.5, 0.82, 1

DSWA

DSWB

SPDT1

SPDT2

1μF

0.01μF

1μF

MAX1329

Figure 28. Optical Reflectometry Application with Dual LED and Single Photodiode

1 2 ... 60 61 62 63 64 65 66 67 68 69 70 ... 77 78

MAX1329/MAX1330 1

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