AD7745 / AD7746 / AD7747 Capacitance-to-Digital Converter Design Guide
Complete application note for the AD774x CDC family: circuit design, shielding, conversion rate selection, and sourcing guidance for the AD7745, AD7746, and AD7747.
Last updated: June 2026
Bottom Line: When choosing a multi-channel digital potentiometer from Analog Devices' AD5204/AD5206/AD8403 family, the three decisions that matter most are channel count (4-channel AD5204/AD8403 vs. 6-channel AD5206), resistance value (1 kΩ, 10 kΩ, 50 kΩ, or 100 kΩ end-to-end), and package footprint (SOIC-24, TSSOP-24, or LFCSP-32). All three ICs share a 3-wire SPI interface, 256-position resolution (8-bit), and ±30 V maximum operating voltage, so the right selection is driven by your channel budget, impedance needs, and PCB space constraints — not by interface compatibility.
What Is a Multi-Channel Digital Potentiometer?
A digital potentiometer (digipot) replaces a mechanical potentiometer with a semiconductor element that accepts digital commands to set wiper position. The Analog Devices AD5204, AD5206, and AD8403 are SPI-controlled quad- and hex-channel digipots that operate from a single 2.7 V–5.5 V supply rail. Each channel contains a resistive ladder of 255 resistor segments and a wiper that taps any of 256 nodes, corresponding to resistance values from 0 Ω (wiper at terminal A) to the full-scale nominal value (wiper at terminal B). Resolution is 8 bits (256 steps), giving approximately 0.4 % per LSB step for fine-grain trimming. Unlike mechanical pots, these devices hold their position in volatile (power-off reset) CMOS memory and accept increments via daisy-chain SPI.
Channel Count: AD5204 (4-ch) vs. AD5206 (6-ch) vs. AD8403 (4-ch)
Channel count is the first filter. The AD5204BRZ10 and AD8403ARUZ1 each integrate 4 independent wiper channels in a 24-pin package, while the AD5206BRZ10 fits 6 channels in the same 24-pin SOIC footprint by dedicating 3 pins per channel pair. If your design requires tone control (bass/mid/treble/gain = 4 knobs), choose the AD5204 or AD8403. If you need 6-band graphic equalization, an audio AGC with 6 gain stages, or a 6-channel test fixture, the AD5206 saves one full package by replacing two 4-channel devices. The AD8403 and AD5204 are pin-compatible and functionally similar; their primary difference is that the AD8403 carries a longer production history and broader stock availability at distribution.
Resistance Value: 1 kΩ, 10 kΩ, 50 kΩ, or 100 kΩ
All three devices are offered in four end-to-end resistance values:
| Suffix | End-to-End R | Typical Application |
|---|---|---|
| …1 | 1 kΩ | Low-impedance drive, audio volume, RF attenuators |
| …10 | 10 kΩ | General-purpose gain setting, sensor bridge trimming |
| …50 | 50 kΩ (AD5206/AD8403) | Mid-range bias networks, reference voltage dividers |
| …100 | 100 kΩ | High-impedance feedback networks, ADC input scaling |
For audio applications, 10 kΩ (AD5204BRZ10, AD5206BRZ10) is the most common choice because it balances thermal noise, drive current, and op-amp input impedance. For precision trimming in instrumentation amps, 1 kΩ (AD8403ARUZ1) reduces the wiper resistance error (nominally 50–75 Ω) to a smaller percentage of total scale. For high-impedance voltage dividers on microcontroller ADC inputs, 100 kΩ (AD5204BRZ100) minimizes quiescent current below 50 µA per channel.
Package Options: SOIC, TSSOP, and LFCSP
Each device is available in multiple packages. SOIC-24 (wide body, 0.3" pitch) suits prototype breadboards and hand-soldering. TSSOP-24 (0.65 mm pitch) shrinks the footprint to approximately 8.7 × 4.4 mm² and is preferred in production SMT lines with reflow capability. The LFCSP-32 variant (AD5204BCPZ10-REEL) adds an exposed thermal pad and is slightly larger (5 × 5 mm) but improves thermal dissipation in power-sensitive applications. TSSOP parts carry a BRUZ or ARUZ suffix; SOIC parts carry a BRZ or ARZ suffix. Choose TSSOP (e.g., AD5204BRUZ10 or AD8403ARUZ1) when board area is constrained; choose SOIC when manual assembly or rework is required.
SPI Interface and Daisy-Chain Capability
All three devices share the same 3-wire SPI-compatible interface: CS (chip select), CLK (clock up to 25 MHz), and SDI (serial data input). Programming a wiper requires a 10-bit word: 2 address bits select the channel, and 8 data bits set the 256-position value. CS must return high to latch the register. Multiple AD5204 or AD5206 devices can be daisy-chained on a single SPI bus by connecting SDO of the first device to SDI of the next, eliminating the need for separate CS lines per device. This reduces GPIO usage on MCUs when controlling 8–24 channels from a single microcontroller. The AD8403 uses an identical protocol and is fully daisy-chain compatible with the AD5204. For SPI timing details, refer to the Analog Devices ADIsimPE simulation environment or download the relevant datasheet via FindMyChip search.
Supply Voltage and Power Consumption
All three ICs operate from a single 2.7 V to 5.5 V supply, making them compatible with 3.3 V CMOS logic (common in ARM Cortex-M MCUs) and legacy 5 V TTL systems without level shifting. Quiescent supply current is typically 1 µA at 3 V and 3 µA at 5 V — negligible even in battery-powered designs. The maximum code-independent wiper current is 1 mA per channel at 5 V, which determines the minimum load resistance that can be driven without exceeding wiper current limits. For audio applications passing AC signals above 1 kHz, verify that the RC time constant formed by the wiper resistance (50–75 Ω typ.) and load capacitance does not roll off the bandwidth below your target frequency.
Volatile vs. Non-Volatile Memory
The AD5204, AD5206, and AD8403 store wiper positions in volatile SRAM — registers reset to the midscale (128/255) position on power-up. This behavior is correct for applications that restore wiper values from a host MCU's NVM on each boot (e.g., an audio DSP that reads stored presets from SPI flash). If your application requires non-volatile retention without a host processor — such as a field-calibration trimmer in an unattended sensor node — consider Analog Devices' AD5262 (2-channel, EEPROM) or AD5235 (dual 1024-position, EEPROM) instead. For most industrial and audio applications, the volatile AD5204/AD5206/AD8403 family is preferred because EEPROM-backed digipots have a write-endurance limit (typically 50,000–100,000 cycles) that matters for frequently updated control loops.
Recommended Products Comparison Table
| Product | Channels | Resistance | Package | Key Use Case | Link |
|---|---|---|---|---|---|
| AD5204BRZ10 | 4-ch | 10 kΩ | SOIC-24 | General gain/volume control, prototyping | View |
| AD5204BRUZ10 | 4-ch | 10 kΩ | TSSOP-24 | SMT production, compact 4-ch designs | View |
| AD5204BCPZ10-REEL | 4-ch | 10 kΩ | LFCSP-32 | Thermal-critical or QFN-preferred layouts | View |
| AD5206BRZ10 | 6-ch | 10 kΩ | SOIC-24 | 6-band EQ, 6-channel calibration fixtures | View |
| AD8403ARUZ1 | 4-ch | 1 kΩ | TSSOP-24 | Low-impedance RF/audio attenuation | View |
Selection Decision Flowchart
Step 1 — How many channels do you need?
- ≤ 4 channels → AD5204 or AD8403 (same channel count, different legacy)
- 5–6 channels → AD5206 (saves one package slot vs. two AD5204s)
6 channels → daisy-chain multiple AD5206 devices on one SPI bus
Step 2 — What end-to-end resistance do you need?
- < 5 kΩ or audio drive into 600 Ω loads → choose 1 kΩ (AD8403ARUZ1 or AD5204BRZ1)
- General gain/volume/filter → choose 10 kΩ (AD5204BRZ10, AD5206BRZ10)
- High-impedance feedback or ADC scaling → choose 100 kΩ (AD5206BRZ100, AD8403ARZ100)
Step 3 — What package does your PCB require?
- Hand-assembly or breadboard prototype → SOIC-24 (BRZ/ARZ suffix)
- SMT production run → TSSOP-24 (BRUZ/ARUZ suffix)
- Thermal pad required or QFN-preferred layout → LFCSP-32 (BCPZ suffix, AD5204 only)
Step 4 — Do you need non-volatile retention on power-down?
- Yes → consider AD5262 / AD5235 (EEPROM variants, outside AD5204 family)
- No → stay with AD5204 / AD5206 / AD8403 (volatile, midscale reset)
FAQ
What is the difference between the AD5204 and AD8403? The AD5204 and AD8403 are functionally nearly identical 4-channel, 256-position, 10-bit SPI digipots from Analog Devices, sharing the same pin-out and protocol. The key practical difference is production history: the AD8403 was introduced earlier and has broader authorized distributor stock worldwide. The AD5204 is the current-production catalog part with LFCSP packaging options not available on the AD8403. Both are rated from −40 °C to +85 °C and operate from 2.7 V–5.5 V.
Can I use the AD5204 or AD5206 in audio applications? Yes. The AD5204 and AD5206 are widely used for digital volume control, tone adjustment, and gain setting in audio systems. The 10 kΩ and 50 kΩ variants are the most common choices, as their impedance matches standard op-amp feedback networks. Total harmonic distortion (THD) is typically −70 dB at 1 kHz with a 1 V RMS signal and a 10 kΩ load, which is adequate for consumer and prosumer audio. For audiophile-grade designs requiring THD below −90 dB, dedicated audio digipots with true zero-crossing detection (such as the DS1882) may be preferred.
What SPI clock rate does the AD5204 support? The AD5204, AD5206, and AD8403 all support SPI clock rates up to 25 MHz, making them compatible with the high-speed SPI peripherals on STM32, ESP32, and most ARM Cortex-M microcontrollers. The 10-bit serial word is clocked in MSB-first. CS must be deasserted (high) between channel writes to latch each register; back-to-back writes require CS to return high for at least one clock period between transactions.
Do the AD5204/AD5206/AD8403 require any external components? These devices require only a decoupling capacitor (100 nF, X7R, placed within 2 mm of VDD) and pull-up resistors on SPI lines if the host MCU I/O is open-drain. No external clock, crystal, or reference voltage is needed. For ESD protection on wiper terminals exposed to board connectors, a low-capacitance TVS diode (e.g., PRTR5V0U2X) is recommended to stay within the ±30 V absolute maximum wiper voltage specification.
Where can I source AD5204, AD5206, and AD8403 at competitive prices? FindMyChip connects buyers with 200+ verified distributors, providing price transparency and authenticated stock for the entire Analog Devices digipot family. Submit a quote request to compare pricing across multiple channels and package variants, or search FindMyChip for real-time inventory across authorized sources.
Conclusion
The AD5204 (4-channel), AD5206 (6-channel), and AD8403 (4-channel) digital potentiometer family from Analog Devices covers the vast majority of multi-channel SPI digipot applications with a unified interface and four resistance values. Use the AD5204 or AD8403 when 4 channels suffice; step up to the AD5206 when 5–6 channels are required in a single package. Choose SOIC for prototyping, TSSOP for SMT production, and LFCSP when a thermal pad is beneficial. If supply availability or pricing is a concern, search FindMyChip to compare real-time inventory across 200+ authenticated distributors and submit a consolidated quote request for your BOM.