MAX1285BESA - 12-Bit 300ksps SAR ADC with Internal Ref | Maxim Integrated
MPN: MAX1285BESA ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $13.29 | $13.29 |
| 10 | $11.96 | $119.60 |
| 100 | $10.63 | $1,063.00 |
| 500 | $9.3 | $4,650.00 |
| 1,000 | $7.97 | $7,970.00 |
MAX1285BESA Overview
What is a SAR ADC? A successive-approximation-register analog-to-digital converter (SAR ADC) is a category of precision data converter that uses a binary-search feedback technique to digitize an analog input one bit at a time per clock cycle. SAR ADCs sit at the lower edge of the data-converter hierarchy alongside sigma-delta ADCs and pipeline ADCs, and are favored where low latency, deterministic sampling, and modest resolution (typically 8 to 18 bits) are required. SAR ADCs are widely used in industrial process control, precision instrumentation, and battery-powered sensor front-ends because they consume essentially no static current between conversions and offer a small, single-cycle pipeline delay that simplifies feedback-loop design.
Key features of the MAX1285BESA include a 300 ksps sampling rate at the low-voltage supply, a high-bandwidth track/hold amplifier, an SPI/QSPI/MICROWIRE-compatible serial interface, an internal +2.5 V reference, ±1 LSB INL and ±1 LSB DNL, and a hardware-/software-configurable shutdown mode that drops supply current below 1 µA. The wide input line is provided through a single-ended analog input; the digital section shares the same supply rail. A 3-wire serial interface minimizes board-routing complexity and keeps opto-isolator count low in industrial modules.
Technically, the MAX1285 family core is built around a capacitive-charge-redistribution DAC and a precision on-chip bandgap-derived +2.5 V reference. Compared with the pin-compatible MAX1284, the MAX1285 trades 4.5V-5.5V operation for 2.7V-3.6V operation while keeping 8-pin SOIC footprint compatibility with the wider MAX128x series. Power consumption at 300 ksps is around 6 mW, dropping to microamp levels in shutdown for battery-friendly designs.
Typical applications include data acquisition boards, pen-digitizers, portable instrumentation, medical instrumentation, process control loops, and battery-powered sensor signal chains. The wide input line gives designers one part number to span hand-held meters and lab instruments.
When designing with this device, focus on input RC network noise below the LSB: drive the analog input with a low-output-impedance buffer and a properly-sized RC anti-alias filter, since the wide input stage injects kickback charge on each conversion. Plan for 16.5 SCLK cycles per conversion and budget 3.0 µs acquisition time so that the internal sample capacitor settles to within ±0.5 LSB before the next conversion starts.
Drop-in alternatives for MAX1285BESA — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with MAX1285BESA (same form factor and footprint) — differing in Package, Resolution, Input Type, RoHS Status, Converter Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MAX1285BESA+
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285BESA+T
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285BCSA+
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285BCSA+T
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285BCSA-T
✅ Drop-In✓ In Stock
$4.89 / Unit
View Datasheet →MAX1285AESA
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285AESA+
✅ Drop-In📋 Reference alternative (not in catalog)
MAX1285BESA Maximum Ratings & Electrical Characteristics
| Part Number | MAX1285BESA |
| Manufacturer | Maxim Integrated (now Analog Devices) |
| Converter Type | SAR ADC (Successive Approximation Register) |
| Resolution | 12 bits |
| Sampling Rate | 300 ksps |
| Number of Channels | 1 input |
| Supply Voltage (Analog/Digital) | 2.7 V to 3.6 V (single supply) |
| Internal Reference | +2.5 V (integrated) |
| Interface Type | SPI / QSPI / MICROWIRE-compatible serial |
| INL (Integral Nonlinearity) | ±1 LSB (max) |
| DNL (Differential Nonlinearity) | ±1 LSB (max) |
| Operating Temperature | -40 C to +85 C (industrial) |
| Package | 8-pin SOIC (3.90 mm / 0.154 inch width) |
| Mounting Type | Surface Mount |
| Power Consumption (300 ksps) | Approximately 6 mW |
| Shutdown Current | < 1 µA |
| RoHS Status | Compliant |
MAX1285BESA Pin Configuration
| Pin 1 | VDD — Positive supply voltage, 2.7V to 3.6V |
| Pin 2 | AIN — Analog input channel |
| Pin 3 | GND — Ground |
| Pin 4 | REF — Reference voltage (internal +2.5V, factory-trimmed; no external cap needed for B grade) |
| Pin 5 | CS — Active-low chip-select input |
| Pin 6 | DOUT — Serial data output (MSB-first, 12-bit result) |
| Pin 7 | SCLK — Serial clock input |
| Pin 8 | SHDN — Active-high shutdown control (low = normal operation) |
Typical Applications
MAX1285BESA is suitable for 6 applications: Data Acquisition (DAQ) Systems, Pen Digitizers and Touch Panels, Portable Instrumentation, Medical Instrumentation, Process Control Loops, Battery-Powered Sensor Signal Chains.
Data Acquisition (DAQ) Systems
The MAX1285BESA fits multi-channel data-acquisition front-ends where each channel needs 12-bit precision at moderate speed. Its 300 ksps throughput at 2.7V-3.6V single supply and 3-wire SPI output simplify the interface to a host microcontroller or DSP. With ±1 LSB INL/DNL and an internal +2.5V reference, it delivers sufficient signal accuracy for transducer-weight, temperature, and voltage measurements in industrial DAQ boards, where the wide operating-temperature range (-40 to +85 C) and small 8-pin SOIC footprint reduce BOM cost.
Recommended
Pen Digitizers and Touch Panels
The MAX1285BESA is well suited to pen-digitizer signal chains that sample pen-position analog signals at moderate rates. The 300 ksps throughput at the low-voltage supply handles multi-axis pen-position decoding, while the 3-wire SPI interface simplifies wiring to the host microcontroller. With 6 mW at full speed and <1 µA in shutdown, the part can be duty-cycled to extend battery life in cordless digitizers. The internal +2.5V reference eliminates one external reference IC, reducing PCB area in space-constrained stylus designs.
Recommended
Portable Instrumentation
The MAX1285BESA is well suited to battery-powered handheld instruments that need 12-bit precision on a single cell or 3.3V rail. The 2.7V-3.6V single supply accepts a lithium-ion battery pack (3.0V-4.2V) via a low-dropout regulator, while the 3-wire SPI interface minimizes host pin count. The hardware SHDN pin drops supply current below 1 µA between conversions, extending battery life for handheld multimeters and field-portable test gear. The small 8-SOIC footprint and 6 mW power consumption suit handheld form factors.
Recommended
Medical Instrumentation
The MAX1285BESA's low-voltage single-rail architecture fits medical signal chains that need 12-bit precision at moderate throughput. The 300 ksps throughput handles ECG and pulse-oximetry front-ends where sampling rates are typically 100-500 sps per channel. The internal +2.5V reference eliminates one precision component, reducing BOM cost in patient-monitoring devices. According to the Maxim datasheet, the part's 2-wire shutdown mode draws <1 µA, extending battery life in wearable patient monitors while keeping the medical-grade precision of the 12-bit SAR architecture.
Recommended
Process Control Loops
The MAX1285BESA is a fit for industrial process-control signal chains that need 12-bit precision at moderate speed with low-voltage operation. The 3-wire SPI interface is well suited to opto-isolated industrial modules, since only three digital lines need to cross the isolation barrier. The 2.7V-3.6V supply accepts a 3.3V regulated post-isolation rail, and the internal +2.5V reference eliminates one external reference IC at the isolated node. The industrial temperature range (-40 to +85 C) supports factory-floor deployments without thermal management.
Recommended
Battery-Powered Sensor Signal Chains
The MAX1285BESA's low-voltage architecture fits sensor signal chains that need to digitize low-bandwidth analog signals on a single lithium cell. The 2.7V-3.6V supply accepts a direct Li-ion connection (with regulator), while the internal +2.5V reference powers the sensor bridge or thermistor chain. The SHDN pin enables duty-cycled conversion for ultra-low quiescent current (<1 µA between samples). At 300 ksps, the part handles the bandwidth of strain-gauge, thermistor, and pressure-sensor signal chains in wireless sensor nodes and IoT edge devices.
Recommended
Recommended Products Summary
Engineering reference data for MAX1285BESA — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MAX1285BESA+ | MAX1285BCSA+ | MAX1285AESA+ |
|---|---|---|---|---|
| Brand | Maxim Integrated | Maxim Integrated | Maxim Integrated | Maxim Integrated |
| Package | 8-SOIC | 8-SOIC - same | 8-SOIC - same | 8-SOIC - same |
| Sampling Rate | 300 ksps | 300 ksps | 300 ksps | 300 ksps |
| Supply Voltage | 2.7V to 3.6V | 2.7V to 3.6V | 2.7V to 3.6V | 2.7V to 3.6V (with external REF) |
| Reference | Internal +2.5V (B grade) | Internal +2.5V (B grade) | Internal +2.5V (B grade) | External (A grade, REF pin) |
| Operating Temperature | -40 C to +85 C | -40 C to +85 C | 0 C to +70 C | -40 C to +85 C |
| Resolution | 12 bits | 12 bits | 12 bits | 12 bits |
| Lead-Free Finish | No (non-+ variant) | Yes (Pb-free) | Yes (Pb-free) | Yes (Pb-free) |
Key Differentiators
- Wide-input industrial temperature range (vs MAX1285BCSA+)
- Internal reference, no external IC needed (vs MAX1285AESA+)
- Pb-free lead-free finish for non-stock compliance (vs MAX1285BESA (this part))
- Single-supply 2.7V-3.6V operation for 3.3V systems (vs MAX1284BESA (5V))
Design Notes
The MAX1285BESA's wide input stage injects kickback charge on each conversion; drive the AIN pin with a low-output-impedance buffer (such as the MAX4238 or OPA333 with the MAX4239) and place a properly-sized RC anti-alias filter at the ADC input. Estimated: with a 50 ohm buffer and a 1 kohm / 100 pF filter, kickback settles within approximately 1.0 us. Budget 3.0 us acquisition time per the datasheet to ensure the internal sample capacitor settles to within ±0.5 LSB before the next conversion starts.
Place a 0.1 µF ceramic bypass capacitor as close as possible to the VDD pin (within 3 mm) and a 1 µF bulk capacitor at the supply-rail entry point. Route the SCLK, CS, and DOUT lines away from the AIN analog trace to minimize digital-to-analog crosstalk. According to the Maxim datasheet, the REF pin does not require an external capacitor on the MAX1285B grade, but a 0.1 µF ceramic at REF is good practice for noise-sensitive designs that bypass the internal reference.
Use the SHDN pin to duty-cycle the ADC for ultra-low quiescent current. According to the Maxim datasheet, shutdown current is below 1 µA, enabling battery-powered designs that sample intermittently. Wake-up time from SHDN is approximately 0.5 µs; include this in the timing analysis for low-duty-cycle sampling patterns. Estimated: at 1% duty cycle (300 ksps bursts of 100 conversions per second), average supply current drops from 2 mA continuous to approximately 25 µA average.
Do not exceed the absolute-maximum VDD of 6.0V; the MAX1285BESA is a 3V-only part. Applying 5V to the VDD pin will permanently damage the part. According to the datasheet, the MAX1284 is the 5V variant of this family - use it for 5V systems. Also, ensure CS is held low for the entire 16.5-clock conversion cycle; an early CS transition aborts the conversion and corrupts the DOUT result.
Compliance Information
RoHS compliant per Maxim product page. Non-+ variant is non-Pb-free; choose MAX1285BESA+ for Pb-free finish. Not AEC-Q100 qualified - this part targets industrial/commercial applications, not automotive.
