Part A
AD7945BRZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 3622 PCS
- Package
- SOIC-20
- Series
- Acquisição de dados - Convertedores digitais para analógicos (DAC)
Replacement verdict
Not a drop-in replacement
The AD7945BRZ and AD7940BRM are not drop-in replacements for one another. Although both are Analog Devices 14-bit successive-approximation ADCs, they differ in resolution, digital interface, package, and reference architecture, so a direct substitution is not possible without redesign.
Different resolution
Different digital interface
Different package
Different reference architecture
Parts at a glance
Part B
AD7940BRM
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 6116 PCS
- Package
- TSSOP-8
- Series
- Acquisição de dados - Analogo para Convertedores Digitais (ADC)
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD7945BRZ | AD7940BRM | Why it matters |
|---|---|---|---|
| Resolution | 12 bits | 14 bits | Resolution determines the smallest analog signal change the ADC can distinguish; a 14-bit part offers finer quantization than a 12-bit part. |
| Architecture | Current-steering R-2R DAC-based (voltage output) | Successive approximation register (SAR) | The AD7945 is a DAC, while the AD7940 is an ADC; the architecture defines the fundamental function and cannot be substituted directly. |
| Converter Function | Digital-to-analog converter (DAC) | Analog-to-digital converter (ADC) | A DAC converts digital codes to analog voltages, whereas an ADC converts analog inputs to digital codes; these are opposite functions and are not functionally interchangeable. |
| Number of Channels | 1 | 1 | Single-channel devices suit point conversions; channel count affects how many signals can be handled per package. |
| Interface Type | Parallel (12-bit) | Serial (SPI/QSPI/MICROWIRE/DSP-compatible) | Parallel interfaces need more pins but offer high throughput; serial interfaces save pins and suit compact or isolated designs. |
| Supply Voltage | 3.3 V to 5 V (single supply) | 2.5 V to 5.5 V (single supply) | Supply range determines compatibility with the system rail; the AD7940 supports lower voltages, enabling use in low-power 2.5 V systems. |
| Package | 20-lead SOIC (R-20) | 8-lead MSOP (RM-8) | Package footprint and pin count affect PCB layout and board space; the 8-lead MSOP is significantly smaller than the 20-lead SOIC. |
| Operating Temperature Range | -40°C to +85°C | -40°C to +85°C | The temperature range indicates the environments in which the part is guaranteed to meet specifications. |
| Data Rate / Update Rate | 4.2 MSPS (DAC update rate) | 100 kSPS (ADC throughput) | Update/throughput rate defines how fast conversions can occur; the DAC updates much faster than the ADC can sample, reflecting their different roles. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD7945BRZ | AD7940BRM |
|---|---|---|
| Supplier | - | Analog Devices Inc.,Rochester Electronics, LLC |
| Part Status | Active | Obsolete |
| Number of Bits | 12 | 14 |
| Sampling Rate(Per Second) | - | 100k |
| Number of Inputs | - | 1 |
| Input Type | - | Single Ended |
| Data Interface | Parallel | SPI, DSP |
| Configuration | - | S/H-ADC |
| Ratio - S / H: ADC | - | 1:1 |
| Number of A/D Converters | - | 1 |
| Architecture | R-2R | SAR |
| Reference Type | External | Supply |
| Voltage - Supply, Analog | 5V | 2.5V ~ 5.5V |
| Voltage - Supply, Digital | 5V | 2.5V ~ 5.5V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Number of D/A Converters | 1 | - |
| Settling Time | 600µs (Typ) | - |
| Output Type | Current - Unbuffered | - |
| Differential Output | No | - |
| INL / DNL(LSB) | ±0.5 (Max), ±0.5 (Max) | - |
Frequently asked questions
What are the key architectural differences between the AD7945BRZ and AD7940BRM?
The AD7945BRZ is a 12-bit, 1.75 MSPS successive-approximation (SAR) analog-to-digital converter with a parallel interface, while the AD7940BRM is a 14-bit, 100 kSPS SAR ADC with a serial (SPI/QSPI/MICROWIRE/DSP-compatible) interface. The AD7945BRZ offers higher throughput but lower resolution, whereas the AD7940BRM provides higher resolution at a lower sampling rate.
Are the AD7945BRZ and AD7940BRM pin-compatible or package-compatible?
No. The AD7945BRZ is supplied in a 20-lead SOIC (R-20) package, while the AD7940BRM is supplied in an 8-lead MSOP (RM-8) package. The pin counts, pin functions, and PCB land patterns differ, so they are not drop-in replacements for one another.
How do the supply voltage and reference requirements compare?
Both devices operate from a single 2.7 V to 5.5 V supply. The AD7945BRZ uses an external reference (REF IN) and supports a reference range of 0.5 V to VDD, while the AD7940BRM also requires an external reference applied to its VREF pin. Designers should verify the specific reference voltage and decoupling requirements in each respective datasheet.
How do the digital interfaces differ between the two parts?
The AD7945BRZ provides a 12-bit parallel data bus with standard CS and RD control lines, making it suitable for direct connection to parallel microcontrollers or DSPs. The AD7940BRM uses a serial interface compatible with SPI, QSPI, MICROWIRE, and DSP standards, which reduces pin count and is preferable when board space or pin availability is limited.
What are the throughput and resolution trade-offs when choosing between them?
The AD7945BRZ delivers 12-bit resolution at up to 1.75 MSPS, making it appropriate for higher-speed signal acquisition. The AD7940BRM delivers 14-bit resolution at up to 100 kSPS, making it appropriate for higher-precision, lower-speed measurements. The choice depends on whether the application prioritizes sampling rate or dynamic range/accuracy.
Can the AD7940BRM directly replace the AD7945BRZ in an existing design?
No. Beyond the package and pin-count differences, the interface type (serial versus parallel), resolution (14-bit versus 12-bit), and maximum throughput (100 kSPS versus 1.75 MSPS) differ. A direct substitution would require PCB redesign, firmware changes, and revalidation against the target system requirements.
What are the typical power consumption characteristics of each device?
Both parts are designed for low-power operation from a single 2.7 V to 5.5 V supply. The AD7945BRZ consumes power proportional to its 1.75 MSPS throughput, while the AD7940BRM is optimized for low power at 100 kSPS. Exact supply current and power figures should be taken from the respective manufacturer datasheets for the specific operating conditions.