ADC121C021CIMKX NSC [National Semiconductor], ADC121C021CIMKX Datasheet - Page 27

• Manufacturer Part Number: ADC121C021CIMKX
• Description: I2C-Compatible, 12-Bit Analog-to-Digital Converter (ADC) with Alert Function
• Manufacturer: NSC [National Semiconductor]

2.0 Applications Information
2.1 TYPICAL APPLICATION CIRCUIT
A typical application circuit is shown in Figure 18. The analog
supply is bypassed with a capacitor network located close to
the ADC121C021. The ADC uses the analog supply (V
its reference voltage, so it is very important that V
clean as possible. Due to the low power requirements of the
ADC121C021, it is possible to use a precision reference as a
power supply. The pull-up resistors (R
by the controller's supply. It is important that the pull-up re-
sistors are pulled to the same voltage potential V
This will ensure that the logic levels of all devices on the bus
are compatible. If the controller's supply is noisy, an appro-
2.2 BUFFERED INPUT
A bufferred input application circuit is shown in Figure 19. The
analog input is buffered by National's LMP7731. The non-in-
verting amplifier configuration provides a buffered gain stage
for a single ended source. This application circuit is good for
P
) should be powered
FIGURE 18. Typical Application Circuit
FIGURE 19. Buffered Input Circuit
A
A
be kept as
is set to.
A
) as
27
priate bypass capacitor should be added between the
controller's supply pin and the pull-up resistors. For Hs-mode
applications, this bypass capacitance will improve the accu-
racy of the ADC.
The value of the pull-up resistors (R
characteristics of each particular I
tion describes how to choose an appropriate value. As a
general rule-of-thumb, we suggest using a 1kΩ resistor for
Hs-mode bus configurations and a 5kΩ resistor for Standard
or Fast Mode bus configurations. Depending upon the bus
capacitance, these values may not be sufficient to meet the
timing requirements of the I
the I
single-ended sensor interface. The input must have a DC bias
level that keeps the ADC input signal from swinging below
GND or above the supply (+5V in this case).
The LM4132, with its 0.05% accuracy over temperature, is an
excelent choice as a reference source for the ADC121C021.
2
C specification for further information.
2
C bus specification. Please see
30020921
2
C bus. The I
P
30020920
) depends upon the
2
www.national.com
C specifica-