MAX135CWI - 15-Bit Low-Power ADC with Parallel Interface
N.º de pieza: MAX135CWI ✓ Activo| Cant. | Precio unitario | Total |
|---|---|---|
| 1 | $33.43 | $33,43 |
| 10 | $30.1 | $301,00 |
| 100 | $26.8 | $2.680,00 |
| 500 | $23.4 | $11.700,00 |
| 1.000 | $18.4 | $18.400,00 |
MAX135CWI Descripción general
An integrating ADC (also called a dual-slope or multi-slope converter) is a class of analog-to-digital converters that integrates the unknown input for a fixed time, then de-integrates against a known reference while counting clock pulses. Multi-slope variants like the MAX135 extend the basic dual-slope topology with additional integration phases that cancel dielectric-absorption errors and high-order integrator non-idealities. In the broader taxonomy the MAX135 belongs to the integrating-ADC family of ADCs, which sits under the data-converter category of mixed-signal ICs in power-management and signal-conditioning systems. This architecture is naturally suited to high-resolution, low-frequency measurements where noise rejection (especially 50 Hz/60 Hz line-frequency rejection) outweighs conversion speed.
Key differentiating specifications include: 15-bit binary resolution (extending to ~18 bits with averaging), 16 conversions-per-second guaranteed throughput, dual-polarity differential input (typically +/- supply rails), low 125 uA typical supply current, single +5 V analog supply with the same supply also powering the parallel digital interface, and an on-chip oscillator that removes the need for an external clock. The WSOIC-28 package has an exposed thermal pad for improved heat spreading and a wide body that simplifies hand-soldering and rework.
The MAX135 uses Super LSB (least significant bit) sub-LSB information and on-chip digital averaging to achieve 18-bit effective resolution. The integrating topology provides inherent rejection of mains-frequency noise (both 50 Hz and 60 Hz), making the part suitable for direct connection to slow analog signals such as thermistor bridges, strain-gauge load cells, pH probes, and other low-bandwidth precision analog-front-ends. The chip-select and read-strobe logic supports direct connection to 8-bit or 16-bit parallel microports without external glue logic.
Typical applications include digital panel meters and bench-top multimeters, industrial process-control analog input modules, weigh-scale and force-measurement signal chains, precision temperature-measurement (RTD and thermocouple) front-ends, and battery monitoring in portable test equipment. The wide input range and parallel data bus also simplify interface to legacy microcontrollers and FPGA-based data acquisition (DAQ) front-ends.
When designing with the MAX135, observe that the integrating topology requires the input to remain stable during the integration window; add an input buffer (op-amp follower) for high-source-impedance sensors. Use a clean analog ground plane and decouple VDD with both 10 uF bulk and 100 nF ceramic caps placed within 10 centimetres of the supply pad.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet, including parametric proximity scoring and same-brand-first alternative ordering for engineers sourcing the MAX135CWI today.
Alternativas directas para MAX135CWI — mismo encapsulado, compatible pin a pin. Se excluyen las piezas de otro encapsulado que requieren retrabajo de la PCB.
Herramienta de comparación rápida — seleccione piezas alternativas para compararlas lado a lado:
MAX135CWI+
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
MAX135CWI+T
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
MAX135EWI+
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
MAX135EWI+T
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
MAX135CWI Valores máximos y características eléctricas
| Resolución | 15 bit (binary), 18 bits effective with on-chip Super-LSB averaging |
| Conversion Rate (specified) | 16 conversions/second (tested), up to ~6x faster possible |
| Conversion Architecture | Multi-slope integrating ADC |
| Number of Input Channels | 1 (single-channel differential input) |
| Input Polarity | Differential, bipolar (dual supply +/- or pseudo-bipolar single supply) |
| Output Interface | Parallel (8-bit/16-bit bus compatible, CS and RD strobes) |
| Output Coding | Binary |
| Analog Supply Voltage | +5 V single supply |
| Supply Current (typical) | 125 uA |
| On-chip Clock | Yes (internal oscillator, no external clock required) |
| Encapsulado | 28-pin WSOIC (wide-body SOIC, SOIC-Wide-28) |
| Operating Temperature Range (CWI suffix) | 0C to +70C (commercial) |
| Tipo de montaje | Surface Mount |
| Estado RoHS | Compliant (MAX135CWI+ lead-free version) |
Configuración de pines de MAX135CWI
| Pin 1 | IN- — Differential analog negative input |
| Pin 2 | IN+ — Differential analog positive input |
| Pin 3 | AGND — Analog ground |
| Pin 4 | REF- — Negative reference input |
| Pin 5 | REF+ — Positive reference input |
| Pin 6 | VDD — Analog +5 V supply |
| Pin 7 | CAP — Integration capacitor pin |
| Pin 8 | OSC — Oscillator capacitor / select (enable) |
| Pin 9 | DGND — Digital ground |
| Pin 10 | TEST — Test mode (per datasheet) |
| Pin 11 | RD — Read strobe (active low) |
| Pin 12 | CS — Chip select (active low) |
| Pin 13 | HBEN — High-byte enable |
| Pin 14 | D14 — Parallel data bit 14 (MSB) |
| Pin 15 | D13 — Parallel data bit 13 |
| Pin 16 | D12 — Parallel data bit 12 |
| Pin 17 | D11 — Parallel data bit 11 |
| Pin 18 | D10 — Parallel data bit 10 |
| Pin 19 | D9 — Parallel data bit 9 |
| Pin 20 | D8 — Parallel data bit 8 |
| Pin 21 | D7 — Parallel data bit 7 |
| Pin 22 | D6 — Parallel data bit 6 |
| Pin 23 | D5 — Parallel data bit 5 |
| Pin 24 | D4 — Parallel data bit 4 |
| Pin 25 | D3 — Parallel data bit 3 |
| Pin 26 | D2 — Parallel data bit 2 |
| Pin 27 | D1 — Parallel data bit 1 |
| Pin 28 | D0 — Parallel data bit 0 (LSB) |
Aplicaciones típicas
MAX135CWI es adecuado para 6 aplicacións: Digital Panel Meters and Bench Multimeters, Weigh-Scale and Load-Cell Signal Chain, Industrial Process Control Analog Inputs, Precision Temperature Measurement Front-End, Battery Monitoring in Portable Test Equipment, Legacy Microcontroller and FPGA DAQ Front-End.
Digital Panel Meters and Bench Multimeters
The MAX135CWI's 15-bit binary output with 18-bit effective resolution via Super-LSB averaging makes it ideal for digital panel meters and 4-1/2 digit bench-top multimeters. The multi-slope integrating topology delivers greater than 80 dB of 50/60 Hz mains noise rejection, which eliminates the need for shielded enclosures in typical lab environments. The MAX135CWI accepts the +/-200 mV to +/-2 V full-scale signal typical of multimeter front-ends directly, and the parallel data bus feeds the LCD/LED driver logic without glue logic. Power consumption of 125 uA on a single +5 V supply keeps battery-powered multimeter designs competitive against SAR-ADC alternatives. Pair the MAX135CWI with a low-offset op-amp buffer such as the Analog Devices AD8628 for the highest-accuracy input stage.
Recomendado
Weigh-Scale and Load-Cell Signal Chain
Load-cell bridges in industrial weigh scales demand DC-to-low-frequency resolution at microvolt-level signals, which is precisely the niche where integrating ADCs excel. The MAX135CWI's 16 sps tested throughput and inherent 50/60 Hz rejection remove the burden of post-processing digital filters that sigma-delta alternatives would otherwise require. The MAX135CWI accepts the bridge differential output directly across its IN+ and IN- pins when excited by the on-chip reference, simplifying the BOM. The 15-bit binary output feeds directly into the host MCU for display and tare operations. Compared with a 24-bit sigma-delta such as the ADS1231, the MAX135CWI trades settling time for absolute accuracy without requiring precision external capacitors or crystals.
Recomendado
Industrial Process Control Analog Inputs
Process-control analog input modules typically scan 4-20 mA or 0-10 V signals from field transmitters at low bandwidth, requiring high noise rejection rather than high speed. The MAX135CWI's multi-slope integrating architecture provides better than 80 dB normal-mode rejection at 50/60 Hz, eliminating the digital filtering burden typical of SAR converters in PLC and DCS analog input cards. The MAX135CWI's parallel interface integrates directly with 8-bit and 16-bit microports common in legacy PLC designs. The single +5 V supply and 125 uA quiescent current simplify isolated supply designs, since the low current draw places minimal stress on the DC-DC converter feeding the isolation barrier. Industrial designers choose the MAX135EWI+ variant when field equipment must operate from -40C to +85C.
Recomendado
Precision Temperature Measurement Front-End
RTD (PT100/PT1000) and thermocouple temperature measurements require microvolt-level resolution at sub-Hz bandwidth, with 50/60 Hz mains pickup being the dominant noise source. The MAX135CWI's integrating topology provides that rejection without digital filters, while the 15-bit binary output plus Super-LSB averaging yields 18-bit effective resolution for high-accuracy thermocouple cold-junction compensation loops. The MAX135CWI accepts the differential signal from the RTD bridge directly when excited by the internal 2.5 V reference, removing the need for a separate reference IC. Low 125 uA quiescent current allows the MAX135CWI to share the +5 V rail with thermocouple-amplifier circuitry such as the AD1126 without overheating the analog ground plane. Industrial designs specify the MAX135EWI+ for outdoor temperature data loggers.
Recomendado
Battery Monitoring in Portable Test Equipment
Battery-powered test instruments require ADC current consumption that does not unduly drain the host battery, especially during standby. The MAX135CWI draws only 125 uA typical from a single +5 V supply, which translates to less than 0.7 mW power consumption - negligible compared to typical LCD and processor budgets in portable DMM and oscilloscope designs. The integrating topology provides free 50/60 Hz rejection, eliminating the post-processing MCU cycles that would otherwise wake the system from sleep. The MAX135CWI is well suited to voltmeter and coulomb-counter front-ends where DC accuracy matters more than acquisition speed. Battery chargers and UPS monitors frequently use the MAX135CWI alongside a current-sense amplifier such as the MAX4080 for complete battery-state monitoring.
Recomendado
Legacy Microcontroller and FPGA DAQ Front-End
Many legacy industrial and embedded designs use 8051, Z80, 68HC11, or similar 8-bit/16-bit microcontrollers that lack modern SPI or I2C peripherals, but offer parallel data buses. The MAX135CWI's parallel interface, complete with chip-select (CS) and read-strobe (RD) signals, connects directly to these legacy microports without glue logic - a major benefit over SPI-only modern ADCs. FPGA-based DAQ cards frequently instantiate the MAX135CWI as a verification reference, taking advantage of the high effective resolution and the deterministic integrating conversion time. The MAX135CWI also suits motor-control and encoder-interface front-ends where analog feedback from current shunts is captured at low bandwidth. Compared with SPI-based ADCs the parallel interface saves several I/O pins but trades speed for simplicity.
Recomendado
Resumen de productos recomendados
Datos de referencia de ingeniería para MAX135CWI — comparación, orientación de diseño e información de cumplimiento.
Guía de selección
Comparación con alternativas
| Parámetro | Este producto | MAX135CWI+ | MAX135CWI+T | MAX135EWI+ | MAX135EWI+T |
|---|---|---|---|---|---|
| Brand | Analog Devices (formerly Maxim Integrated) | Analog Devices - same | Analog Devices - same | Analog Devices - same | Analog Devices - same |
| Package | WSOIC-28 (wide-body SOIC) | WSOIC-28 - same | WSOIC-28 - same | WSOIC-28 - same | WSOIC-28 - same |
| Resolution | 15 bit (binary) / 18 bit effective (Super-LSB) | 15 bit / 18 bit effective - same | 15 bit / 18 bit effective - same | 15 bit / 18 bit effective - same | 15 bit / 18 bit effective - same |
| Conversion Rate (tested) | 16 sps | 16 sps - same | 16 sps - same | 16 sps - same | 16 sps - same |
| Operating Temperature Range | 0C to +70C (commercial) | 0C to +70C - same | 0C to +70C - same | -40C to +85C (extended) | -40C to +85C (extended) |
| RoHS / Lead-Free | Non-RoHS (legacy MAX135CWI without +) | RoHS-compliant / lead-free | RoHS-compliant / lead-free | RoHS-compliant / lead-free | RoHS-compliant / lead-free |
| Packaging Format | Tube | Tube | Tape and Reel | Tube | Tape and Reel |
| Architecture | Multi-slope integrating | Multi-slope integrating - same | Multi-slope integrating - same | Multi-slope integrating - same | Multi-slope integrating - same |
Diferenciadores clave
- Multi-slope integrating architecture delivers inherent 50/60 Hz rejection without digital filtering (frente a MAX135CWI+)
- On-chip Super-LSB averaging extends 15-bit output to 18-bit effective resolution (frente a MAX135EWI+)
- Parallel 15-bit data bus connects directly to legacy 8/16-bit microports (frente a MAX135CWI+T)
Notas de diseño
Place a 10 uF tantalum bulk capacitor and a 100 nF ceramic decoupling capacitor within 10 centimetres of the VDD pin to suppress supply-induced integrator drift. The integrating architecture of the MAX135CWI is highly sensitive to high-frequency supply noise because the integrator sums input and supply-rejection-rail errors over the entire conversion window - poor decoupling translates directly into gain and offset error. Use a dedicated analog ground plane tied to AGND at a single location to avoid ground-loop currents from digital return paths crossing under the differential input traces.
Route the differential analog inputs (IN+ and IN-) as a tightly-coupled matched-impedance differential microstrip, keeping traces parallel and equal length to within 5 millimetres. The MAX135CWI's input common-mode rejection at 50/60 Hz depends on the symmetry of the input traces, so any imbalance degrades effective resolution directly. Add a low-leakage input protection circuit (e.g. clamping diodes or TVS arrays) when interfacing with sensor bridges that can produce over-voltage transients during field installation or fault conditions. Avoid running the parallel digital bus under or across the analog traces - use a ground trace or ground plane as a guard between the analog and digital sections of the PCB.
Do not connect a capacitor directly to the CAP pin without consulting the datasheet's recommended integration-capacitor section, or the conversion gain will be incorrect. The MAX135CWI's internal oscillator requires the correct external CAPACRO capacitor value to set the integrator de-integration time constant; using the wrong value changes full-scale range and may cause linearity errors exceeding 1 LSB. When migrating to the MAX135EWI+ extended-temperature variant, verify the integrator timing across temperature - the internal oscillator frequency drift can shift the full-scale calibration. Do not bypass the on-chip reference - external reference decoupling on REF+ and REF- is mandatory to prevent reference-noise pickup that would couple directly into the conversion result.
Información de cumplimiento
The MAX135CWI (without + suffix) is the legacy non-RoHS variant with lead-bearing termination. The MAX135CWI+ is the RoHS-compliant lead-free version. AEC-Q100 is not applicable as this is a precision data converter rather than an automotive-qualified IC; the MAX135AEMG is not offered - industrial-temperature EWI suffix exists instead.
