Part A
AD7656BSTZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 3438 PCS
- Package
- LQFP-64
- Series
- Acquisição de dados - Analogo para Convertedores Digitais (ADC)
Replacement verdict
Not a drop-in replacement
The AD7656BSTZ and AD7651AST are not drop-in replacements for one another. The AD7656BSTZ is a six-channel simultaneous-sampling bipolar ADC in a 64-lead LQFP, while the AD7651AST is a single-channel unipolar ADC in a 48-lead LQFP. They differ in channel count, input configuration, package footprint, and digital interface, so a direct board-level substitution is not possible without redesign.
Different channel count
Different input configuration
Different footprint
Different digital interface
Parts at a glance
Part B
AD7651AST
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 965 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 | AD7656BSTZ | AD7651AST | Why it matters |
|---|---|---|---|
| Number of ADC Channels | 6 | 1 | Determines how many independent analog signals can be sampled simultaneously; a 6-channel part cannot be substituted by a single-channel part in multi-channel systems. |
| Resolution | 16 bits | 16 bits | Both provide 16-bit resolution, so precision and LSB size are comparable, which is important for measurement accuracy. |
| Sampling Rate | 250 kSPS | 100 kSPS | Maximum throughput affects the highest signal frequency that can be digitized; the slower part may not meet bandwidth requirements of the faster design. |
| Input Type | Single-ended (true bipolar) | Single-ended (unipolar/bipolar) | Input configuration must match the sensor or signal conditioning; mismatched input ranges can require additional level-shifting circuitry. |
| Interface | Parallel / Serial (SPI) | Serial (SPI) | The host microcontroller or FPGA must support the available digital interface; a parallel-only host cannot use a serial-only device without rework. |
| Supply Voltage | 5 V analog, 5 V digital | 5 V analog, 5 V digital | Matching supply rails simplifies power design and ensures compatible logic levels with surrounding circuitry. |
| Package | 64-lead LQFP | 48-lead LQFP | Footprint and pin count must match the PCB layout; different packages require board redesign and cannot be drop-in replaced. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Identical temperature ratings ensure both parts suit the same environmental conditions and reliability requirements. |
| Power Consumption | Approx. 100 mW (typical) | Approx. 25 mW (typical) | Power budget differences affect thermal design and supply sizing; the higher-power part may exceed the thermal envelope of a low-power design. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD7656BSTZ | AD7651AST |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | iCMOS® | PulSAR® |
| Part Status | Active | Obsolete |
| Number of Bits | 16 | 16 |
| Sampling Rate(Per Second) | 250k | 100k |
| Number of A/D Converters | 6 | 1 |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Number of Inputs | 6 | - |
| Input Type | Single Ended | - |
| Data Interface | SPI, Parallel, DSP | - |
| Configuration | S/H-ADC | - |
| Ratio - S / H: ADC | 1:1 | - |
| Architecture | SAR | - |
| Reference Type | External, Internal | - |
| Voltage - Supply, Analog | 5V | - |
| Voltage - Supply, Digital | 5V | - |
| Features | Simultaneous Sampling, True Bipolar | - |
Frequently asked questions
What are the key architectural differences between the AD7656BSTZ and the AD7651AST?
The AD7656BSTZ is a 16-bit, 6-channel, simultaneous-sampling successive-approximation (SAR) ADC with a 250 kSPS throughput rate per channel, housed in a 64-lead LQFP package. The AD7651AST is a 16-bit, single-channel, 100 kSPS SAR ADC in a 48-lead LQFP package. The AD7656 integrates six ADCs with six track-and-hold amplifiers for simultaneous sampling, while the AD7651 provides one channel with a single track-and-hold.
Can the AD7656BSTZ and AD7651AST be used interchangeably in an existing design?
No. The two devices differ in channel count (6 vs 1), package footprint (64-lead LQFP vs 48-lead LQFP), pinout, throughput rate (250 kSPS vs 100 kSPS), and external interface configuration. They are not pin-compatible or functionally interchangeable, so a direct drop-in substitution is not possible without PCB and firmware redesign.
What are the maximum throughput rates of the AD7656BSTZ and AD7651AST?
The AD7656BSTZ offers a maximum throughput of 250 kSPS per channel with all six channels sampling simultaneously. The AD7651AST offers a maximum throughput of 100 kSPS for its single channel. Both are SAR-type ADCs, but the AD7656 provides higher per-channel speed and parallel multi-channel acquisition.
What analog input voltage ranges do these two ADCs support?
Both the AD7656BSTZ and AD7651AST support bipolar analog input ranges of ±10 V and ±5 V, selectable via configuration. This makes both devices suitable for industrial signal acquisition where bipolar front-end signals are common, though the AD7656 provides six simultaneous channels versus one on the AD7651.
What digital interfaces do the AD7656BSTZ and AD7651AST provide?
The AD7656BSTZ provides a parallel interface (with word/byte modes) plus a serial interface, supporting high-speed readback of six channels. The AD7651AST provides a parallel interface for its single channel. System designers must account for these interface differences when migrating between the two parts.
How do the power supply requirements compare between the AD7656BSTZ and AD7651AST?
Both devices operate from a 5 V analog supply (AVDD) and require a separate digital supply (DVDD) for the interface, typically 2.7 V to 5.25 V. The AD7656BSTZ, with six ADCs, draws higher total supply current than the single-channel AD7651AST, so power budget and thermal planning differ between the two designs.
Which applications typically favor the AD7656BSTZ versus the AD7651AST?
The AD7656BSTZ is suited to multi-phase power monitoring, motor control, and power-quality analyzers where six simultaneous channels are needed to capture correlated signals. The AD7651AST is suited to single-channel precision measurement, such as isolated sensor acquisition or single-axis monitoring, where one 16-bit channel at 100 kSPS is sufficient.
Do the AD7656BSTZ and AD7651AST share the same package and pinout?
No. The AD7656BSTZ is supplied in a 64-lead LQFP package, while the AD7651AST is supplied in a 48-lead LQFP package. The pin counts and pin assignments differ, so PCB land patterns and routing are not compatible between the two devices.