MAX5156BEEE Просмотр технического описания (PDF) - Maxim Integrated

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MAX5156BEEE

Low-Power, Dual, 12-Bit Voltage-Output DACs with Configurable Outputs

Maxim Integrated 

Low-Power, Dual, 12-Bit Voltage-Output DACs

with Configurable Outputs

Digital Calibration and

Threshold Selection

Figure 13 shows the MAX5156/MAX5157 in a digital

calibration application. With a bright value applied to

the photodiode (on), the DAC is digitally ramped up

until it trips the comparator. The microprocessor stores

this high calibration value. Repeat the process with a

dim light (off) to obtain the dark current calibration. The

microprocessor then programs the DAC to set an out-

put voltage that is the midpoint of the two calibration

values. Applications include tachometers, motion sens-

ing, automatic readers, and liquid clarity analysis.

Digital Control of Gain and Offset

The two DACs can be used to control the offset and

gain for curve-fitting nonlinear functions, such as trans-

ducer linearization or analog compression/expansion

applications. The input signal is used as the reference

for the gain-adjust DAC, whose output is summed with

the output from the offset-adjust DAC. The relative

weight of each DAC output is adjusted by R1, R2, R3,

and R4 (Figure 14).

REF_

+5V/+3V

VDD

MAX5156

MAX5157

µP

DIN

DAC _

DGND

AGND

Figure 13. Digital Calibration

V+

PHOTODIODE

FB_

OUT_

R

V+

VOUT

V-

+5V/+3V

VIN

CS

DIN

SCLK

CL

VREF

VDD

REFA

DACA

DACB

REFB

MAX5156

MAX5157

DGND

AGND

Figure 14. Digital Control of Gain and Offset

FBA

R1

OUT_A

R2

OUT_B

R3

VOUT

R4

FBB

VOUT = [GAIN] - [OFFSET]

[( )( )( )] [( )( )] =

VIN

NA

4096

R2 1+ R4

R1+R2 R3

VREF

NB

4096

R4

R3

NA IS THE NUMERIC VALUE OF THE INPUT CODE FOR DACA.

NB IS THE NUMERIC VALUE OF THE INPUT CODE FOR DACB.

______________________________________________________________________________________ 15

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