MAX5156ACEE-T Maxim Integrated, MAX5156ACEE-T Datasheet - Page 15

• Manufacturer Part Number: MAX5156ACEE-T
• Description: Digital to Analog Converters - DAC
• Manufacturer: Maxim Integrated

Specifications of MAX5156ACEE-T

• Number Of Converters: 2
• Number Of Dac Outputs: 2
• Resolution: 12 bit
• Interface Type: QSPI, SPI, Serial (3-Wire, Microwire)
• Settling Time: 15 us
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• Package / Case: QSOP-16
• Minimum Operating Temperature: 0 C
• Output Type: Voltage
• Supply Voltage - Max: 5.5 V
• Supply Voltage - Min: 4.5 V
• Voltage Reference: External

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.
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).
Figure 14. Digital Control of Gain and Offset
Low-Power, Dual, 12-Bit Voltage-Output DACs
Digital Control of Gain and Offset
______________________________________________________________________________________
SCLK
V
DIN
V
REF
CS
CL
IN
Digital Calibration and
+5V/+3V
Threshold Selection
DGND
MAX5156
MAX5157
V
DD
DACA
DACB
REFA
REFB
AGND
with Configurable Outputs
FBA
OUT_A
OUT_B
FBB
Figure 13. Digital Calibration
V
OUT
NA IS THE NUMERIC VALUE OF THE INPUT CODE FOR DACA.
NB IS THE NUMERIC VALUE OF THE INPUT CODE FOR DACB.
P
=
=
R3
[
[
R1
(
GAIN
DIN
V
IN
]
4096
NA
-
DGND
REF_
[
OFFSET
R2
)(
DAC _
R1+R2
MAX5156
MAX5157
R2
]
)(
1+
R4
R4
R3
+5V/+3V
V
) (
] [
DD
AGND
V
REF
V
OUT
4096
NB
)( )
OUT_
FB_
R4
R3
]
R
V+
PHOTODIODE
V+
V-
V
OUT
15