Part A
AD7685BRMZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 1331 PCS
- Package
- TFSOP-10
- Series
- Data Acquisition - Analog to Digital Converters (ADC)
Replacement verdict
Compatible functional replacement candidate
The AD7688BRM is a strong functional replacement candidate for the AD7685BRMZ, sharing the same 16-bit SAR architecture, 250 kSPS throughput, and MSOP-10 footprint, though the differential input configuration and reference architecture require validation before substitution in existing designs.
Resolution and Throughput
High match
Package and Pinout
High match
Input Configuration
Validation required
Reference Architecture
Validation required
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD7685BRMZ | AD7688BRM | Why it matters |
|---|---|---|---|
| Resolution (bits) | 16 | 16 | Both are 16-bit ADCs, so resolution is identical and not a differentiator for substitutability. |
| Sampling Rate (max) | 250 kSPS | 500 kSPS | The AD7688 offers twice the throughput, which matters for higher-bandwidth signal acquisition. |
| Input Type | Pseudo-differential (single-ended) | Fully differential | Input topology affects signal conditioning, common-mode rejection, and whether the part can directly replace the other in a given front-end. |
| Number of Input Channels | 1 | 1 | Both are single-channel devices, so channel count is not a differentiator. |
| Interface | SPI / QSPI / MICROWIRE / DSP compatible | SPI / QSPI / MICROWIRE / DSP compatible | Identical serial interface simplifies drop-in replacement at the digital interface level. |
| Supply Voltage (analog) | 2.7 V to 5.5 V | 4.5 V to 5.5 V | The AD7685 supports lower analog supplies, enabling 3.3 V operation that the AD7688 cannot support. |
| Package | 10-lead MSOP | 10-lead MSOP | Same package footprint allows physical board compatibility between the two parts. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Identical temperature ratings mean environmental constraints are the same for both. |
| Power Consumption (typical) | 3.5 mW at 5 V, 250 kSPS | 15 mW at 5 V, 500 kSPS | Power budget differs significantly; the AD7688 draws more due to higher throughput, affecting thermal and energy-sensitive designs. |
Need help validating a replacement?
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD7685BRMZ | AD7688BRM |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Part Status | Active | Obsolete |
| Number of Bits | 16 | 16 |
| Series | PulSAR® | - |
| Sampling Rate(Per Second) | 250k | - |
| Number of Inputs | 1 | - |
| Input Type | Pseudo-Differential | - |
| Data Interface | SPI, DSP | - |
| Configuration | S/H-ADC | - |
| Ratio - S / H: ADC | 1:1 | - |
| Number of A/D Converters | 1 | - |
| Architecture | SAR | - |
| Reference Type | External | - |
| Voltage - Supply, Analog | 2.3V ~ 5.5V | - |
| Voltage - Supply, Digital | 2.3V ~ 5.5V | - |
| Operating Temperature | -40°C ~ 85°C | - |
Frequently asked questions
What are the key differences between the AD7685BRMZ and the AD7688BRM?
The AD7685BRMZ is a 16-bit, 250 kSPS PulSAR analog-to-digital converter, while the AD7688BRM is a 16-bit, 500 kSPS PulSAR ADC. The AD7688BRM offers twice the throughput of the AD7685BRMZ. Both are available in a 10-lead MSOP package and share a similar pinout, but they differ in maximum sampling rate and some dynamic performance specifications.
Are the AD7685BRMZ and AD7688BRM pin-compatible?
Yes, both devices are offered in a 10-lead MSOP (RM) package and share the same pin configuration, including VDD, VIO, GND, REF, IN+, IN-, CNV, SDO, SCK, and SDI. This pin compatibility allows the AD7688BRM to be used as a higher-throughput drop-in replacement for the AD7685BRMZ in many designs, provided the rest of the system supports the higher sampling rate.
What is the maximum sampling rate of each device?
The AD7685BRMZ has a maximum throughput of 250 kSPS. The AD7688BRM has a maximum throughput of 500 kSPS. The higher rate of the AD7688BRM requires the digital host to support the corresponding serial clock frequency and conversion timing.
Do both ADCs use the same serial interface?
Yes, both the AD7685BRMZ and AD7688BRM use a SPI-compatible serial interface with separate CNV, SCK, SDO, and SDI pins. The interface supports daisy-chain operation and readback during conversion. The AD7688BRM's higher throughput means the serial clock must be able to run fast enough to read the 16-bit result within the shorter conversion cycle.
What is the resolution and architecture of these ADCs?
Both the AD7685BRMZ and AD7688BRM are 16-bit successive-approximation register (SAR) ADCs based on Analog Devices' PulSAR architecture. They provide no missing codes at 16 bits and are designed for high-accuracy, low-power data acquisition applications.
What are the supply voltage requirements for these devices?
Both devices operate from a single analog supply (VDD) of 2.7 V to 5.5 V and a separate digital I/O supply (VIO) of 1.8 V to 5.5 V, allowing direct interfacing to low-voltage digital logic. The reference voltage (REF) is applied externally and can range up to VDD.
Can the AD7688BRM replace the AD7685BRMZ in an existing design?
In many cases yes, because the two devices are pin-compatible and share the same package and interface. However, the replacement must be validated: the digital host must support the 500 kSPS rate of the AD7688BRM, the reference and analog front-end must meet the dynamic performance requirements at the higher throughput, and power dissipation should be reviewed. Always confirm against the respective manufacturer datasheets before substitution.