8.3.1 Supply Voltage (V+)

The ADC128D818 operates with a supply voltage, V+, that has a range between 3 V to 5.5 V. Take care to bypass this pin with a parallel combination of 1-µF (electrolytic or tantalum) capacitor and 0.1-µF (ceramic) bypass capacitor.

8.3.2 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 2.56 V. The second option is to source VREF externally through pin 1 of ADC128D818. In this case, the external VREF will operate in the range of 1.25 V 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.

8.3.3 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.

8.3.3.1 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 must be connected to ADC128D818’s GND pin. In theory, INx can be of any value between 0V and (VREF-3LSb/2), where LSb = VREF/2¹².

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.

Figure 24. Single-Ended Configuration

8.3.3.2 Pseudo-Differential Input

Pseudo-differential mode is defined as the positive input voltage applied differentially to the ADC128D818, as shown in Figure 25. The input that is digitized is (ΔVIN = IN+ - IN–), where (IN+ - IN–) is (IN0-IN1), (IN3-IN2), (IN4-IN5), or (IN7-IN6). Be aware of this input configuration because the order is swapped. In theory, ΔVIN can be of any value between 0 V and (VREF – 3LSb/2), where LSb = VREF/2¹².

By using this pseudo-differential input, small signals common to both inputs are rejected. Thus, operation with a pseudo-differential input signal will provide better performance than with a single-ended input. See Modes of Operation for more information.

Figure 25. Pseudo-Differential Configuration

8.4.1 Modes of Operation

ADC128D818 allows 4 modes of operation, as summarized in the following table. Set the desired mode of operation using the Advanced Configuration Register — Address 0Bh, bits [2:1]).

8.5.1 Interface

The Serial Bus control lines include the SDA (serial data), SCL (serial clock), and A0-A1 (Serial Bus Address) pins. The ADC128D818 can only operate as a slave. The SCL line only controls the serial interface, and all of other clock functions within ADC128D818 are done with a separate asynchronous internal clock.

When the Serial Bus Interface is used, a write will always consists of the ADC128D818 Serial Bus Address byte, followed by the Register Address byte, then the Data byte. Figure 26 and Figure 27 are two examples showing how to write to the ADC128D818.

There are two cases for a read:

1. If the Register Address is known to be at the desired address, simply read the ADC128D818 with the Serial Bus Address byte, followed by the Data byte read from the ADC128D818. Examples of this type of read can be seen in Figure 28 and Figure 29.
2. If the Register Address value is unknown, write to the ADC128D818 with the Serial Bus Address byte, followed by the desired Register Address byte. Then restart the Serial Communication with a Read consisting of the Serial Bus Address byte, followed by the Data byte read from the ADC128D818. See Figure 30 and Figure 31 for examples of this type of read.

The Serial Bus Address can be found in the next section, and the Register Address can be found in Register Maps. For more information on the I²C Interface, refer to NXP's "I²C-Bus Specification and User Manual", rev. 03.

8.5.1.2.1 Example Writes and Reads

Figure 26. Serial Bus Interface Write Example 1 - Internal Address Register Set Only

Figure 27. Serial Bus Interface Write Example 2 - Internal Address Register Set With Data Byte Write

Figure 28. Serial Bus Interface Read Example 1 - Single Byte Read With Preset Internal Address Register

Figure 29. Serial Bus Interface Read Example 2 - Double Byte Read With Preset Internal Address Register

Figure 30. Serial Bus Interface Read Example 3 - Single Byte Read With Internal Address Set Using a Repeat Start

Figure 31. Serial Bus Interface Read Example 4 - Double Byte Read With Internal Address Set Using a Repeat Start

8.6.1 ADC128D818 Internal Registers

8.6.2 Configuration Register — Address 00h

Default Value [7:0] = 0000_1000 binary

8.6.3 Interrupt Status Register — Address 01h

Default Value [7:0] = 0000_0000 binary

8.6.4 Interrupt Mask Register — Address 03h

Default Value [7:0] = 0000_0000 binary

8.6.5 Conversion Rate Register — Address 07h

Default Value [7:0] = 0000_0000 binary

8.6.6 Channel Disable Register — Address 08h

Default Value [7:0] = 0000_0000 binary

• This register must only be programmed when the device is in shutdown mode, that is, when the ‘START’ bit of the “Configuration Register’ (address 00h) = 0.
• Whenever this register is programmed, all of the values in the Channel Reading Registers and Interrupt Status Registers will return to their default values.

8.6.7 One-Shot Register — Address 09h

Default Value [7:0] = 0000_0000 binary

8.6.8 Deep Shutdown Register — Address 0Ah

Default Value [7:0] = 0000_0000 binary

8.6.9 Advanced Configuration Register — Address 0Bh

Default Value [7:0] = 0000_0000 binary

Note: Whenever the Advanced Configuration Register is programmed, all of the values in the Channel Reading Registers and Interrupt Status Registers will return to their default values.

8.6.10 Busy Status Register — Address 0Ch

Default Value [7:0] = 0000_0010 binary

8.6.11 Channel Readings Registers — Addresses 20h – 27h

8.6.12 Limit Registers — Addresses 2Ah – 39h

8.6.13 Manufacturer ID Register — Address 3Eh

Default Value [7:0] = 0000_0001 binary

8.6.14 Revision ID Register — Addresses 3Fh

Default Value [7:0] = 0000_1001 binary