Datasheet

ADC128D818
www.ti.com SNAS483E –FEBRUARY 2010–REVISED MARCH 2013
FUNCTIONAL DESCRIPTION
GENERAL DESCRIPTION
The ADC128D818 provides 8 analog inputs, a temperature sensor, a delta-sigma ADC, an external or internal
VREF option, and WATCHDOG registers on a single chip. An I
2
C Serial Bus interface is also provided. The
ADC128D818 can perform voltage and temperature monitoring for a variety of systems.
The ADC128D818 continuously converts the voltage input to 12-bit resolution with an internal VREF of 0.625mV
LSb (Least Significant bit) weighting, yielding input range of 0V to 2.56V. There is also an external VREF option
that ranges from 1.25V to V+. The analog inputs are intended to be connected to several power supplies present
in a variety of systems. Eight inputs can be configured for single-ended and/or pseudo-differential channels.
Temperature can be converted to a 9-bit two's complement word with resolutions of 0.5°C per LSb.
The ADC128D818 provides a number of internal registers. These registers are summarized in the Table 6
section.
The ADC128D818 supports Standard Mode (Sm, 100kbits/s) and Fast Mode (Fm, 400kbits/s) I
2
C interface
modes of operation. ADC128D818 includes an analog filter on the I
2
C digital control lines that allows improved
noise immunity. The device also supports TIMEOUT reset function on SDA and SCL to prevent I
2
C bus lock-up.
Two tri-level address pins allow up to 9 devices on a single I
2
C bus.
At start-up, ADC128D818 cycles through each measurement in sequence and continuously loops through the
sequence based on the Conversion Rate Register (address 07h) setting. Each measured value is compared to
values stored in the Limit Registers (addresses 2Ah - 39h). When the measured value violates the programmed
limit, the ADC128D818 will set a corresponding interrupt bit in the Interrupt Status Registers (address 01h). An
interrupt output pin, INT, is also available and fully programmable.
SUPPLY VOLTAGE (V+)
The ADC128D818 operates with a supply voltage, V+, that has a range between +3.0V to +5.5V. Care must be
taken to bypass this pin with a parallel combination of 1 µF (electrolytic or tantalum) capacitor and 0.1 µF
(ceramic) bypass capacitor.
VOLTAGE REFERENCES (VREF)
The reference voltage (VREF) sets the analog input range. The ADC128D818 has two options for setting VREF.
The first option is to use the internal VREF, which is equal to 2.56V. The second option is to source VREF
externally via pin 1 of ADC128D818. In this case, the external VREF will operate in the range of 1.25V to V+.
The default VREF selection is the internal VREF. If the external VREF is preferred, use the Advanced
Configuration Register — Address 0Bh to change this setting.
VREF source must have a low output impedance and needs to be bypassed with a minimum capacitor value of
0.1 µF. A larger capacitor value of 1 µF placed in parallel with the 0.1 µF is preferred. VREF of the
ADC128D818, like all ADC converters, does not reject noise or voltage variations. Keep this in mind if VREF is
derived from the power supply. Any noise and/or ripple from the supply that is not rejected by the external
reference circuitry will appear in the digital results. The use of a reference source is recommended. The LM4040
and LM4050 shunt reference families as well as the LM4120 and LM4140 series reference families are excellent
choices for a reference source.
ANALOG INPUTS (IN0 - IN7)
The ADC128D818 allows up to 8 single-ended inputs or 4 pseudo-differential inputs as selected by the modes of
operation. The input types are described in the next subsections.
Single-Ended Input
ADC128D818 allows a maximum of 8 single-ended inputs, where the source's voltage is connected to INx (0 ≤ x
≤ 7). The source’s ground should be connected to ADC128D818’s GND pin. In theory, INx can be of any value
between 0V and (VREF-3LSb/2), where LSb = VREF/2
12
.
To use the device single-endedly, refer to the Modes of Operation section and to bits [2:1] of the Advanced
Configuration Register — Address 0Bh. Figure 24 shows the appropriate configuration for a single-ended
connection.
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