Texas Instruments ADS7844EG4

Overview

ADS7844EG4 from Texas Instruments is a 12-bit, 8-channel SAR analog-to-digital converter with synchronous serial interface, ±1 LSB INL/DNL, 72 dB SINAD, and 200 kHz max throughput at +5 V. It supports single-ended (8 ch) or differential (4 ch) inputs, operates from 2.7 V to 5 V, and integrates an on-chip multiplexer for battery-powered data acquisition systems.

For engineers reviewing the ADS7844EG4 datasheet, ADS7844EG4 pinout, ADS7844EG4 application, or ADS7844EG4 equivalent, key selection considerations include its 20-lead QSOP package, 12-bit resolution with no missing codes, shutdown mode (<1 µW), reference voltage flexibility (0.1 V to V_CC), and compatibility with isolated serial interfaces in remote measurement systems.

Technical Context

The ADS7844EG4 implements a capacitive redistribution successive approximation register (SAR) architecture with integrated sample-and-hold, fabricated in 0.6 µm CMOS. It requires an external clock (f_CLK = 16 × f_SAMPLE) and external reference (100 mV to V_CC), enabling programmable input range scaling and low-noise operation down to 125 kHz at +2.7 V.

Digital control is delivered via an 8-bit serial command byte (S, A2–A0, SGL/DIF, PD1/PD0) that configures channel selection, input mode, and power-down state. The device outputs straight-binary 12-bit data over DOUT synchronized to DCLK falling edge, with BUSY indicating conversion status and CS enabling high-impedance tri-state output control.

Key Specifications

Pinout & Package

ADS7844EG4 is housed in a 20-lead QSOP (DBQ) package with 0.65 mm lead pitch, surface-mount compatible, and RoHS-compliant. Pin functions are electrically validated per TI SBAS100A datasheet Rev. October 2003.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit multichannel SAR ADC applications.

Compared with MAX147BCPP+, ADS7844EG4 offers wider supply range (2.7–5 V), hardware shutdown, and better linearity (±1 LSB vs. ±2 LSB); compared with ADS7841U, it doubles channel count while maintaining identical interface, timing, and power profile - making it optimal for space-constrained multichannel upgrades.

Availability

ADS7844EG4 is available at Aetrix Electronics and suitable for portable instrumentation, industrial process monitoring, and isolated remote data acquisition requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for ADS7844EG4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies, with decades of expertise in precision data converters and industrial-grade ICs.

The ADS7844EG4 belongs to TI's precision SAR ADC product line, designed specifically for low-power, multichannel measurement systems where resolution, linearity, and supply flexibility are critical - including handheld test equipment and distributed sensor networks.

FAQ

What is the maximum sample rate of the ADS7844EG4 and what clock frequency is required?

The ADS7844EG4 achieves up to 200 kHz throughput at +5 V, requiring an external DCLK of 3.2 MHz (f_CLK = 16 × f_SAMPLE). At +2.7 V, max rate drops to 125 kHz with 2 MHz DCLK. The device supports 15-/16-/24-clock conversion modes - actual achievable rate depends on DCLK stability, layout, and power supply decoupling. ADS7844EG4 does not internally generate clocks; all timing is externally controlled.

Does the ADS7844EG4 support true differential input mode, and how is it configured?

Yes, the ADS7844EG4 supports true differential input mode across four channel pairs (e.g., CH0–CH1, CH2–CH3). Configuration is done via the SGL/DIF bit (LOW) and A2–A0 address bits in the 8-bit serial control byte. In differential mode, the COM pin is ignored; the voltage difference between the selected +IN and –IN channels is digitized. This mode provides common-mode rejection and improved noise immunity versus single-ended operation.

What is the function of the COM pin on the ADS7844EG4, and how should it be connected?

The COM pin serves as the analog ground reference for single-ended input mode, defining the zero-volt point for all eight channels. It must be connected to a clean, low-impedance ground or stable reference potential - never left floating. In differential mode, COM is unused. Improper COM connection causes offset errors and non-monotonic behavior. For best performance, route COM with short, low-inductance traces and bypass near the device.

How does the ADS7844EG4 handle power-down, and what is the difference between SHDN and PD1/PD0 bits?

The ADS7844EG4 offers two power-down mechanisms: hardware SHDN (Pin 10, active-low) forces <1 µW consumption instantly, and software-configurable PD1/PD0 bits (in control byte) enable auto power-down between conversions (PD1=PD0=0). SHDN overrides all internal states; PD1/PD0 only affects operation during idle periods. Both methods preserve register state and allow immediate valid conversion upon wake-up - no reinitialization needed for ADS7844EG4.

Can the ADS7844EG4 operate with a reference voltage lower than 1 V, and what impact does that have on performance?

Yes, the ADS7844EG4 accepts VREF as low as 100 mV. However, LSB size scales linearly (e.g., 24 µV at 100 mV), making the ADC more sensitive to noise, offset, and reference instability. Total harmonic distortion and SINAD degrade below ~500 mV reference; noise-limited effective resolution drops. For sub-1 V references, TI recommends low-noise layout, heavy bypassing (0.1 µF + 1 µF), and digital averaging. ADS7844EG4 remains functional but requires careful system-level noise management.