Datasheet

SDA
SCL
I
2
C Serial Interface
Conversion Result
Pointer = 00000000
Pointer
Register
(selects
register to
read from
or write to)
Pointer Address
Highest Conversion
Pointer = 00000111
Lowest Conversion
Pointer = 00000110
Configuration
Pointer = 00000010
Alert Status
Pointer = 00000001
Hysteresis
Pointer = 00000101
High Limit
Pointer = 00000100
Low Limit
Pointer = 00000011
Data
ADC121C021, ADC121C021Q, ADC121C027
www.ti.com SNAS415F –JANUARY 2008–REVISED MARCH 2013
REFERENCE VOLTAGE
The ADC121C021 uses the supply (V
A
) as the reference, so V
A
must be treated as a reference. The analog-to-
digital conversion will only be as precise as the reference (V
A
), so the supply voltage should be free of noise. The
reference should be driven by a low output impedance voltage source.
The Applications section provides recommended ways to drive the ADC reference input appropriately. Refer to
Typical Application Circuit for details.
POWER-ON RESET
An internal power-on reset (POR) occurs when the supply voltage transitions above the power-on reset
threshold. Each of the registers contains a defined value upon POR and this data remains there until any of the
following occurs:
• The first conversion is completed, causing the Conversion Result and Status registers to be updated.
• A different data word is written to a writable register.
• The ADC is powered down.
The internal registers will lose their contents if the supply voltage goes below 2.4V. Should this happen, it is
important that the V
A
supply be lowered to a maximum of 200mV before the supply is raised again to properly
reset the device and ensure that the ADC performs as specified.
INTERNAL REGISTERS
The ADC121C021 has 8 internal data registers and one address pointer. The registers provide additional ADC
functions such as storing minimum and maximum conversion results, setting alert threshold levels, and storing
data to configure the operation of the device. Figure 24 shows all of the registers and their corresponding
address pointer values. All of the registers are read/write capable except the conversion result register, which is
read-only.
Figure 24. Register Structure
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Product Folder Links: ADC121C021 ADC121C021Q ADC121C027