Analog Devices Inc. AD7908BRU

Overview

AD7908BRU from Analog Devices is an 8-bit, 1 MSPS, 8-channel successive approximation ADC with integrated channel sequencer, operating from a single 2.7 V to 5.25 V supply and delivering 6 mW max power dissipation at 3 V. It features SPI/QSPI/MICROWIRE/DSP-compatible serial interface, no pipeline delay, and 20-lead TSSOP packaging for space-constrained industrial data acquisition systems.

For engineers reviewing the AD7908BRU datasheet, AD7908BRU pinout, AD7908BRU application, or AD7908BRU equivalent, key selection criteria include its 8-bit resolution with ±0.2 LSB INL/DNL, 49 dB SINAD at 50 kHz, 0 V to REFIN or 0 V to 2 × REFIN input range configurability, VDRIVE logic-level independence, and automotive-qualified temperature range (−40°C to +125°C).

Technical Context

The AD7908BRU implements a standard SAR architecture with track-and-hold amplifier supporting >8 MHz input bandwidth and precise sampling controlled by CS falling edge. Conversion timing is fully synchronous to SCLK, requiring exactly 16 clock cycles (e.g., 800 ns at 20 MHz), with no latency between sample initiation and result availability.

Its control register enables flexible configuration: RANGE bit selects 0 V to REFIN (straight binary) or 0 V to 2 × REFIN (twos complement); CODING bit sets output format; SEQ and SHADOW bits program channel sequencing order across VIN0–VIN7 inputs. VDRIVE decouples logic interface voltage (2.7 V–5.25 V) from AVDD, enabling direct interfacing with 3 V or 5 V microcontrollers without level shifters.

Key Specifications

Pinout & Package

AD7908BRU is housed in a 20-lead Thin Shrink Small Outline Package (TSSOP) with exposed pad for thermal enhancement and standard JEDEC MS-013AC footprint. Pin functions are validated per Analog Devices Rev. E datasheet Figure 3 and Table 6.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit, multi-channel SAR ADC applications.

Compared with AD7908BRU, AD7918BRU provides 2 extra bits and 12 dB higher SINAD at the cost of increased power and reduced DC accuracy matching; ADS7953IRHBT trades VDRIVE independence and AEC-Q100 compliance for higher resolution and lower static power, requiring additional interface components in heterogeneous systems.

Availability

AD7908BRU is available at Aetrix Electronics and suitable for industrial process monitoring, motor control feedback, and battery management systems requiring stable component supply, long-term lifecycle support, and automotive-grade reliability.

Supply support for AD7908BRU 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

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD7908BRU belongs to the AD7908/AD7918/AD7928 family of high-speed, low-power, multichannel SAR ADCs designed specifically for space- and power-constrained industrial and automotive data acquisition where deterministic timing and channel sequencing are essential.

FAQ

What is the maximum sampling rate supported by the AD7908BRU?

The AD7908BRU supports a maximum throughput rate of 1 MSPS, achieved with a 20 MHz SCLK frequency and 16-cycle conversion time (800 ns). This rate is maintained across the full −40°C to +125°C automotive temperature range and is independent of input channel selection due to its internal sequencer architecture.

Does the AD7908BRU require an external reference voltage?

Yes, the AD7908BRU requires an external 2.5 V ±1% reference applied to the REFIN pin. The device does not include an internal reference; REFIN directly sets the full-scale input range (0 V to REFIN or 0 V to 2 × REFIN) and impacts gain accuracy, with typical REFIN input impedance of 36 kΩ at 1 MSPS.

How does the VDRIVE pin function in the AD7908BRU?

The VDRIVE pin on the AD7908BRU sets the logic threshold levels (0.3×VDRIVE and 0.7×VDRIVE) for all digital interface pins (SCLK, DIN, CS, DOUT), decoupling them from AVDD. This allows direct connection to 3 V or 5 V microcontrollers even when AVDD is at a different voltage, eliminating external level shifters in mixed-voltage designs.

Can the AD7908BRU perform automatic sequential conversion across all eight channels?

Yes, the AD7908BRU includes a programmable channel sequencer controlled via the SEQ and SHADOW bits in its 16-bit control register. Once configured, it automatically cycles through a user-defined subset of VIN0–VIN7 channels in sequence, outputting results with embedded 3-bit channel address bits in each DOUT frame-reducing host software overhead.

What are the absolute maximum ratings for AVDD and REFIN on the AD7908BRU?

The AD7908BRU has an absolute maximum AVDD rating of −0.3 V to +7 V relative to AGND, and REFIN must remain between −0.3 V and AVDD + 0.3 V. Exceeding these limits-even momentarily-may cause permanent damage. For reliable operation, AVDD must be maintained within 2.7 V to 5.25 V, and REFIN must be 2.5 V ±1%.