Part A
AD7656YSTZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 7772 PCS
- Package
- LQFP-64
- Series
- Acquisição de dados - Analogo para Convertedores Digitais (ADC)
Replacement verdict
Compatible functional replacement candidate
The AD7655ASTZRL and AD7656YSTZ are both 16-bit successive-approximation ADCs from Analog Devices, but they differ in channel architecture, package, and interface configuration. The AD7655ASTZRL offers a dual 2-channel multiplexed input in a 48-lead LQFP, while the AD7656YSTZ provides six simultaneous-sampling channels in a 64-lead LQFP. Because the channel count, footprint, and control interface differ, the AD7656YSTZ is not a direct drop-in replacement for the AD7655ASTZRL; substitution requires validation of the system's channel requirements, board layout, and digital timing.
Channel Count
Validation required
Package Type
Validation required
Resolution
High match
Interface Type
Validation required
Parts at a glance
Part B
AD7655ASTZRL
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 1730 PCS
- Package
- LQFP-48
- 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 | AD7655ASTZRL | AD7656YSTZ | Why it matters |
|---|---|---|---|
| Number of ADC Channels | 2 (dual, simultaneous sampling) | 6 (six, simultaneous sampling) | Channel count determines how many analog signals can be digitized; a 6-channel part cannot be substituted where 2 channels suffice, and vice versa for multi-axis/multi-phase systems. |
| Resolution | 16 bits | 16 bits | Both provide 16-bit resolution, so dynamic range and LSB size are comparable, which is important for precision measurement applications. |
| Package / Pin Count | 48-lead LQFP | 64-lead LQFP | Different package footprints and pin counts mean the parts are not drop-in compatible; PCB layout and rework would be required. |
| Sampling Rate (max) | 1 MSPS | 250 kSPS | Maximum throughput affects achievable signal bandwidth and timing margin; the AD7655 supports faster conversion than the AD7656. |
| Analog Input Type | Pseudo-differential (single-ended capable) | True bipolar differential | Input topology determines signal conditioning requirements and common-mode handling; true differential inputs offer better noise immunity and reject ground offsets. |
| Supply Voltage | 5 V analog (AVDD), 5 V digital (DVDD) | 5 V analog (AVDD), 5 V digital (DVDD) | Matching supply rails simplifies power design and ensures comparable input ranges and logic levels. |
| Interface | Parallel and serial (SPI/QSPI/MICROWIRE/DSP) | Parallel and serial (SPI/QSPI/MICROWIRE/DSP) | Both offer flexible host interfaces, so system-level digital connectivity is broadly compatible. |
| Internal Reference | Yes (2.5 V on-chip reference) | Yes (2.5 V on-chip reference) | An internal reference reduces external component count and simplifies design; both parts include one, aiding substitutability. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Identical industrial temperature ratings mean both are suitable for the same environmental conditions. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD7656YSTZ | AD7655ASTZRL |
|---|---|---|
| Series | iCMOS® | PulSAR® |
| Part Status | Active | Active |
| Number of Bits | 16 | 16 |
| Sampling Rate(Per Second) | 250k | 1M |
| Number of Inputs | 6 | 2, 4 |
| Input Type | Single Ended | Pseudo-Differential, Single Ended |
| Data Interface | SPI, Parallel, DSP | SPI, Parallel, DSP |
| Configuration | S/H-ADC | MUX-S/H-MUX-ADC |
| Ratio - S / H: ADC | 1:1 | 2:1 |
| Number of A/D Converters | 6 | 1 |
| Architecture | SAR | SAR |
| Reference Type | External, Internal | External |
| Voltage - Supply, Analog | 5V | 5V |
| Voltage - Supply, Digital | 5V | 5V |
| Features | Simultaneous Sampling, True Bipolar | Simultaneous Sampling |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 85°C |
Frequently asked questions
What are the primary differences between the AD7655ASTZRL and the AD7656YSTZ?
The AD7655ASTZRL is a dual-channel, 16-bit, 1 MSPS successive-approximation ADC with simultaneous sampling, housed in a 48-lead LQFP package. The AD7656YSTZ is a six-channel, 16-bit, 250 kSPS SAR ADC with simultaneous sampling on all six channels, housed in a 64-lead LQFP package. The AD7656YSTZ integrates six ADCs, while the AD7655ASTZRL integrates two.
Are the AD7655ASTZRL and AD7656YSTZ pin-compatible or footprint-compatible?
No. The AD7655ASTZRL uses a 48-lead LQFP package, while the AD7656YSTZ uses a 64-lead LQFP package. The different pin counts and package dimensions mean the PCB land patterns are not interchangeable, and a direct drop-in replacement is not possible without a board redesign.
How do the sampling rates of the AD7655ASTZRL and AD7656YSTZ compare?
The AD7655ASTZRL offers a throughput rate of up to 1 MSPS per channel. The AD7656YSTZ offers a throughput rate of up to 250 kSPS per channel. The AD7655ASTZRL therefore provides a higher per-channel sampling rate, while the AD7656YSTZ provides more simultaneous channels at a lower per-channel rate.
Do both the AD7655ASTZRL and AD7656YSTZ support simultaneous sampling?
Yes. Both devices feature simultaneous sampling architecture. The AD7655ASTZRL simultaneously samples its two input channels, and the AD7656YSTZ simultaneously samples all six of its input channels. This makes both suitable for applications requiring phase-coherent acquisition across multiple channels.
What are the analog input voltage ranges for the AD7655ASTZRL and AD7656YSTZ?
Both devices support selectable analog input ranges. The AD7655ASTZRL offers a 0 V to 5 V unipolar range and a ±10 V bipolar range. The AD7656YSTZ offers a ±10 V bipolar range and a ±5 V bipolar range. Designers should confirm the exact range configuration against the respective manufacturer datasheets for their target operating mode.
What digital interfaces do the AD7655ASTZRL and AD7656YSTZ provide?
Both devices provide a parallel interface and a serial interface for connection to host processors or FPGAs. The AD7655ASTZRL supports a high-speed parallel interface and a serial interface. The AD7656YSTZ also supports parallel and serial interfaces. The specific interface timing and bus-width details should be verified in the respective datasheets.
Which device is better suited for multi-channel simultaneous acquisition systems?
The AD7656YSTZ is better suited when six simultaneous channels are required in a single package, as it integrates six ADCs. The AD7655ASTZRL is appropriate when only two simultaneous channels are needed but a higher per-channel sampling rate of up to 1 MSPS is required. The choice depends on the channel count and throughput requirements of the application.
Can the AD7655ASTZRL be used as a substitute for the AD7656YSTZ in an existing design?
No, not as a direct substitute. The AD7655ASTZRL has two channels versus six on the AD7656YSTZ, a different package and pin count, and a different per-channel throughput. Any substitution would require a board redesign and validation of channel count, sampling rate, input range, and interface compatibility against the manufacturer datasheets.