Analog Devices Inc. AD7940BRM

Overview

AD7940BRM from Analog Devices is a 14-bit successive approximation ADC in a 6-lead SOT-23 package, operating from a single 2.5 V to 5.5 V supply with 100 kSPS throughput and 81 dB SINAD at 10 kHz. It features internal VDD-referenced conversion, no pipeline delay, and SPI/QSPI/MICROWIRE-compatible serial interface. It serves as a compact, low-power analog-to-digital front-end in space-constrained portable instrumentation.

For engineers reviewing the AD7940BRM datasheet, AD7940BRM pinout, AD7940BRM application, or AD7940BRM equivalent, key selection criteria include its 6-lead SOT-23 footprint, 0 V to VDD unipolar input range, 0.5 µA shutdown current, and CS-controlled sampling instant without latency.

Technical Context

The AD7940BRM implements a capacitive DAC-based SAR architecture with track-and-hold acquisition time of 400 ns (sine ≤10 kHz) and aperture jitter of 30 ps typ. Its conversion is initiated on the falling edge of CS and clocked by SCLK, requiring exactly 16 cycles for full 14-bit result output with two leading zeros.

It uses VDD as both power supply and reference source, yielding an LSB size of VDD/16384 and eliminating external reference components. Power management is controlled exclusively via CS timing: normal mode sustains full operation, while early CS deassertion (between 2nd and 10th SCLK edge) triggers full analog circuit shutdown.

Key Specifications

Pinout & Package

AD7940BRM is housed in a 6-lead SOT-23 package (JEDEC MO-178AA), measuring 2.9 mm × 1.6 mm × 1.1 mm, with gull-wing leads and 0.95 mm pitch. Thermal resistance θ_JA is 229.6°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 14-bit SAR ADC applications.

Compared with AD7940BRM, AD7942BRMZ offers differential input but forfeits the integrated VDD reference and SOT-23 compactness, while ADS8320EB/250 provides 16-bit resolution at the cost of higher power and larger packaging-making AD7940BRM optimal for space- and power-constrained single-ended sensor interfaces.

Availability

AD7940BRM is available at Aetrix Electronics and suitable for battery-powered systems, portable medical instruments, and remote data acquisition systems requiring stable component supply and long-term industrial lifecycle support.

Supply support for AD7940BRM 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 AD7940BRM belongs to Analog Devices' precision SAR ADC product line, engineered for ultra-low-power, high-resolution data acquisition in portable and energy-sensitive applications where board space and battery life are critical constraints.

FAQ

What is the absolute maximum analog input voltage for the AD7940BRM?

The absolute maximum analog input voltage for the AD7940BRM is VDD + 0.3 V, per Absolute Maximum Ratings Table 4. Exceeding this risks forward-biasing internal ESD diodes and causing irreversible damage. For safe operation, VIN must remain within 0 V to VDD under normal conditions, as specified in the Analog Input section. The AD7940BRM's input structure includes 25 Ω series resistance and 30 pF capacitance, requiring careful attention to source impedance to maintain THD performance.

Does the AD7940BRM require an external reference voltage?

No, the AD7940BRM does not require an external reference voltage. Its reference is derived internally from VDD, establishing a 0 V to VDD unipolar input range and an LSB size of VDD/16384. This eliminates external reference components and associated layout complexity. However, VDD must be well-decoupled (e.g., 100 nF ceramic + 10 µF tantalum) to ensure stable reference quality. The AD7940BRM's reference architecture is fixed and non-adjustable-no external reference pin exists.

How does the AD7940BRM enter and exit power-down mode?

The AD7940BRM enters power-down mode when CS is deasserted (brought high) between the 2nd and 10th falling edge of SCLK after conversion initiation. This shuts down all analog circuitry, reducing current to 0.5 µA max. To exit, a dummy conversion is performed: CS is pulled low again, initiating a full 16-cycle sequence that restores internal biasing. Power-up time from full power-down is 1 µs typ. The AD7940BRM's power-down behavior is strictly CS-timed and requires no additional control signals.

What digital interface protocols is the AD7940BRM compatible with?

The AD7940BRM is compatible with SPI, QSPI, MICROWIRE, and generic DSP serial interfaces. Its SDATA output is 3-state and synchronized to SCLK falling edges, delivering a 16-bit frame (2 leading zeros + 14-bit result, MSB first). It supports standard mode clock polarity and phase (CPOL = 0, CPHA = 0) and tolerates digital inputs up to 7 V regardless of VDD-enabling direct interfacing with 5 V controllers even when VDD = 3 V. The AD7940BRM's interface requires no configuration registers or initialization sequences.

What is the guaranteed DC accuracy of the AD7940BRM across its supply range?

The AD7940BRM guarantees 14-bit resolution for VDD between 2.5 V and 4.096 V, and 13-bit resolution for VDD > 4.096 V, per Table 2. Integral nonlinearity is ±1 LSB max in the 2.5–4.096 V range and ±2 LSB max above 4.096 V. Offset error is ±6 LSB max and gain error is ±8 LSB max across the full −40°C to +85°C temperature range. These DC specifications are tested and guaranteed-not typical values-and define the worst-case code transition errors affecting measurement repeatability and calibration stability in production systems using the AD7940BRM.