MAX187BCWE+ Maxim Integrated Products, MAX187BCWE+ Datasheet - Page 17

• Manufacturer Part Number: MAX187BCWE+
• Description: IC ADC SRL12BIT 5V 75KSPS 16SOIC
• Manufacturer: Maxim Integrated Products

Specifications of MAX187BCWE+

• Number Of Bits: 12
• Sampling Rate (per Second): 75k
• Data Interface: MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 478mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.50mm Width)
• Number Of Adc Inputs: 1
• Architecture: SAR
• Conversion Rate: 75 KSPs
• Resolution: 12 bit
• Input Type: Voltage
• Interface Type: Serial
• Voltage Reference: Internal 4.096 V
• Supply Voltage (max): 5 V
• Maximum Power Dissipation: 478 mW
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The ADC results are transmitted across a 1500V isola-
tion barrier provided by three 6N136 opto-isolators.
Isolated power must be supplied to the converter and
the isolated side of the opto-couplers. 74HC595 three-
state shift registers are used to construct a 12-bit paral-
lel data output. The timing sequence is identical to the
timing shown in Figure 8. Conversion speed is limited
by the delay through the opto-isolators. With a 140kHz
clock, conversion time is 100µs.
The universal 12-bit parallel data output can also be
used without the isolation stage when a parallel inter-
face is required. Clock frequencies up to 2.9MHz are
possible without violating the 20ns shift-register setup
time. Delay or invert the clock signal to the shift regis-
ters beyond 2.9MHz.
For best performance, use printed circuit boards. Wire-
wrap boards are not recommended. Board layout
should ensure that digital and analog signal lines are
separated from each other. Do not run analog and digi-
tal (especially clock) lines parallel to one another, or
digital lines underneath the ADC package.
Figure 17 shows the recommended system ground
connections. A single-point analog ground (“star”
ground point) should be established at GND, separate
from the logic ground. All other analog grounds should
be connected to this ground. The 16-pin versions also
have a dedicated DGND pin available. Connect DGND
to this star ground point for further noise reduction. No
other digital system ground should be connected to
this single-point analog ground. The ground return to
the power supply for this ground should be low imped-
ance and as short as possible for noise-free operation.
High-frequency noise in the V
affect the ADC’s high-speed comparator. Bypass this
supply to the single-point analog ground with 0.01µF
and 4.7µF bypass capacitors. Minimize capacitor lead
lengths for best supply-noise rejection. If the +5V
power supply is very noisy, a 10Ω resistor can be con-
nected as a lowpass filter to attenuate supply noise
(Figure 17).
Layout, Grounding, Bypassing
______________________________________________________________________________________
+5V, Low-Power, 12-Bit Serial ADCs
DD
power supply may
Figure 17. Power-Supply Grounding Condition
*OPTIONAL
V DD
+5V
R* = 10
0.01 F
4.7 F
AGND
MAX187
MAX189
SUPPLIES
DGND
+5V
CIRCUITRY
DIGITAL
DGND
GND
17