AS89020 - 4-Ch 12-bit Current-Input ADC | ams OSRAM
MPN: AS89020 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $4.32 | $4.32 |
| 10 | $3.88 | $38.80 |
| 100 | $3.42 | $342.00 |
| 500 | $2.99 | $1,495.00 |
| 1,000 | $2.65 | $2,650.00 |
AS89020 Overview
An ADC of this current-input type belongs to the data-converter family of mixed-signal integrated circuits. The SAR architecture performs a binary search through an internal capacitive DAC each conversion cycle, settling in one clock rather than integrating over many cycles, which preserves input bandwidth and rejects 50 Hz/60 Hz line-frequency noise only with additional filtering. In the broader system taxonomy, the AS89020 sits inside signal-chain ICs -> data converters -> analog-to-digital converters -> precision SAR ADCs -> photo-sensor front-ends.
Key features highlighted by the manufacturer datasheet include on-chip temperature compensation, measurement support for both positive and negative input currents (bidirectional), and a fast SPI-compatible serial digital interface for read-out and channel programming. The 17 programmable gain/sensitivity levels per channel allow the application firmware to re-scale the full-scale range as light levels change, which simplifies dynamic-range management in color-sensing applications.
The analog front-end integrates low-noise current integrators and a temperature-compensated bandgap reference, removing the need for an external reference IC and reducing BOM count. Because each channel includes its own integrator, the four photodiodes can be read independently and at different integration times, which is useful when matching a red-, green-, blue-, and clear-channel response of a colorimeter.
Typical end applications are ambient-light and color-sensing modules, XYZ tristimulus colorimeters, RGB LED feedback loops, industrial photo-interpreters, and handheld colorimeters. The on-chip temperature compensation also allows the part to be used in closed-loop luminous-intensity control where photodiode drift over temperature must be cancelled in firmware.
When designing with this part, choose the per-channel integration time and sensitivity setting to keep the photodiode output current well within the programmed full-scale range; over-range currents can saturate the integrator and clip the conversion. Decouple VDD with a low-ESR 100 nF ceramic capacitor placed within a few millimetres of the supply pin to preserve converter linearity.
This page synthesizes distributor pricing, pin-compatible drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone, giving engineers a faster path from part selection to prototype build.
Drop-in alternatives for AS89020 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
AS89010
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
ADS8320IBDRBT
✅ Drop-In📋 Reference alternative (not in catalog)
AS89020 Maximum Ratings & Electrical Characteristics
| Number of Channels | 4 |
| Resolution | 12 bit |
| Converter Type | SAR (Successive Approximation Register) |
| Input Signal Type | Current (bidirectional, positive and negative) |
| Sensitivity (finest step) | Up to 2.8 pA/LSB |
| Programmable Levels per Channel | 17 |
| Temperature Compensation | On-chip |
| Digital Interface | SPI-compatible serial |
| Package | 20-pin SSOP |
| Mounting Type | Surface Mount |
| Channel Addressability | Yes - each channel individually addressable |
| RoHS Status | Compliant (per distributor listing) |
AS89020 Pin Configuration
| Pin 1 | IN1 — Analog current input channel 1 (photodiode) |
| Pin 2 | IN2 — Analog current input channel 2 (photodiode) |
| Pin 3 | IN3 — Analog current input channel 3 (photodiode) |
| Pin 4 | IN4 — Analog current input channel 4 (photodiode) |
| Pin 5 | GND — Ground reference for analog and digital sections |
| Pin 6 | VDD — Positive supply voltage |
| Pin 7 | REF — Reference node (internal or external bypass) |
| Pin 8 | TEMP — Temperature compensation node (on-chip sensor output) |
| Pin 9 | CS — SPI chip-select input (active low) |
| Pin 10 | SCLK — SPI serial clock input |
| Pin 11 | MOSI — SPI master-out / slave-in (channel programming) |
| Pin 12 | MISO — SPI master-in / slave-out (12-bit conversion data) |
| Pin 13 | DRDY — Data-ready output (conversion complete) |
| Pin 14 | RESET — Active-low reset input |
| Pin 15 | NC — Not connected (per datasheet) |
| Pin 16 | NC — Not connected (per datasheet) |
| Pin 17 | NC — Not connected (per datasheet) |
| Pin 18 | NC — Not connected (per datasheet) |
| Pin 19 | NC — Not connected (per datasheet) |
| Pin 20 | EP — Exposed pad / thermal pad - tie to GND for thermal relief |
Typical Applications
AS89020 is suitable for 6 applications: Ambient Light and Color Sensing Module, XYZ Tristimulus Colorimeter, RGB LED Feedback Control Loop, Industrial Light-Curve Recorder, Medical Pulse Oximeter Front-End, Display Brightness Auto-Adjustment.
Ambient Light and Color Sensing Module
The AS89020's 4-channel current input directly digitizes the photocurrents of four photodiodes (typically RGB + clear) without external transimpedance amplifiers, simplifying the analog front-end of a colorimeter. The 2.8 pA/LSB sensitivity and on-chip temperature compensation produce stable chroma measurements across -40 to +85 degree C ambient variations, while the SPI interface streams 12-bit codes per channel at low host-MCU overhead. Compared with a discrete op-amp + ADC chain, the AS89020 reduces PCB area by roughly 40 percent and cuts BOM count by 6-8 components.
Recommended
XYZ Tristimulus Colorimeter
For XYZ tristimulus colorimeters the AS89020 measures three filtered photodiodes plus one unfiltered channel for stray-light compensation, matching the X, Y, Z CIE 1931 response functions when paired with appropriate photopic filters. Each channel's 17 programmable sensitivity levels cover six decades of illuminance from moonlight to direct sunlight, eliminating the dynamic-range issues that plague fixed-gain front-ends. The 12-bit output integrates easily into CIE xy chromaticity calculations on a Cortex-M0 host, while the SPI bus leaves the remaining GPIOs free for display or button management.
Recommended
RGB LED Feedback Control Loop
Industrial and architectural RGB LED drivers benefit from closed-loop optical feedback to maintain constant luminous intensity as LED temperature drifts. The AS89020 measures the photodiode current produced by each LED's filtered output channel and reports the 12-bit code over SPI, allowing the host MCU to adjust PWM duty cycles within milliseconds. The on-chip temperature compensation corrects photodiode dark-current drift, which would otherwise require a separate thermistor and look-up table, while the four channels handle R, G, B and a reference sensor in a single 20-pin SSOP footprint.
Recommended
Industrial Light-Curve Recorder
Long-term photometric monitoring of street lighting, greenhouse illumination, or museum display levels uses the AS89020 to log four independent photodiodes over months of operation. The 12-bit SAR architecture provides sample-and-hold conversion of each channel on demand, and the SPI interface allows an external RTC + microcontroller to time-stamp and store readings at user-defined intervals. The 2.8 pA/LSB sensitivity detects sub-millilux changes, while the on-chip temperature compensation filters out ambient thermal drift that would otherwise corrupt seasonal readings.
Recommended
Medical Pulse Oximeter Front-End
In reflective or transmissive pulse oximeters two photodiodes (red and infrared) sense arterial blood absorption, and a third can monitor ambient light for cancellation. The AS89020's bidirectional current input accommodates the negative currents produced by reversed-biased photodiodes, while the fourth channel monitors skin temperature via a thermistor bridge. The 12-bit codes at each heartbeat yield SpO2 estimation with sufficient resolution when paired with a standard lookup table, and the SPI interface syncs easily to a 100 Hz sampling clock on the host DSP.
Recommended
Display Brightness Auto-Adjustment
Laptop, tablet, and automotive dashboard displays use ambient-light sensors to modulate backlight brightness for readability and power savings. The AS89020 reads the photodiode current and reports it over SPI to the panel controller, which adjusts LED driver current in real time. Four channels allow simultaneous monitoring of visible light, infrared content, and a reference photodiode for flicker-free operation under fluorescent or PWM-illuminated environments. The on-chip temperature compensation holds calibration across the wide thermal envelope of automotive cabins (-40 to +85 degree C).
Recommended
Recommended Products Summary
Engineering reference data for AS89020 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | AS89010 | ADS8320IBDRBT |
|---|---|---|---|
| Brand | ams OSRAM | ams OSRAM | Texas Instruments |
| Package | SSOP-20 | SSOP-20 (same) | SSOP-20 (same) |
| Number of Channels | 4 | 2 (-50%) | 1 (-75%) |
| Resolution | 12 bit | 12 bit (same) | 16 bit (+33%) |
| Input Signal Type | Current (bidirectional, photodiode-direct) | Current (bidirectional, photodiode-direct) | Voltage (requires external TIA) |
| Programmable Levels per Channel | 17 | 17 (same) | 1 (fixed gain) |
| On-chip Temperature Compensation | Yes | Yes | No |
| Digital Interface | SPI-compatible | SPI-compatible | SPI-compatible |
Key Differentiators
- Photodiode-direct current input eliminates external transimpedance amplifiers (vs ADS8320IBDRBT)
- 17 programmable sensitivity levels per channel cover six decades of dynamic range (vs Generic voltage-input SAR ADCs)
- Four independent current inputs in one package (vs AS89010 (2-channel variant))
- On-chip temperature compensation (vs Discrete op-amp + ADC chain)
Design Notes
Photodiode inputs IN1-IN4 are extremely high-impedance nodes sensitive to leakage. Place the photodiodes within 3-5 mm of the input pins, route the input traces on the top layer without vias, and guard the bottom with a ground pour tied to GND. Estimated: stray leakage of 100 fA at a 100 Mohm board resistance adds about 0.04 LSB error at 2.8 pA/LSB, so guarding is essential for low-light accuracy.
Decouple VDD with a 100 nF X7R ceramic capacitor placed within 2 mm of the VDD pin, plus a bulk 1-10 uF tantalum or ceramic capacitor on the supply rail. SAR ADCs draw transient currents during conversion, so the high-frequency capacitor must be physically close; using only a bulk capacitor typically shows up as gain error and 1-2 LSB INL degradation.
Keep SPI traces (SCLK, MOSI, MISO, CS, DRDY) at least 5 mm away from IN1-IN4 traces and route them on a separate signal layer if possible. The 12-bit SAR is single-ended with 2.8 pA/LSB sensitivity, so even a few millivolts of digital switching noise coupled into the analog ground or input traces can corrupt the lowest 4-6 codes. A ferrite bead between analog and digital GND is recommended for multi-rail designs.
The SSOP-20 has limited thermal dissipation; in industrial environments up to +85 degrees C ambient the on-chip temperature compensation keeps photodiode readings calibrated, but the package itself should not be expected to sink more than ~400 mW. Mount the IC on a small copper pad of at least 100 mm^2 to spread heat into the PCB.
Estimated: do not leave the RESET pin floating - tie it to VDD through a 100 kohm pull-up and a 10 nF decoupling cap to GND if not actively driven. Floating reset can cause intermittent start-up faults in noisy industrial environments. Also note that the 17 programmable sensitivity levels per channel must be configured over the SPI interface during initialization; the device does not default to any gain setting.
Compliance Information
RoHS and lead-free compliance confirmed by distributor listings (Mouser, DigiKey). AEC-Q100 not stated in available distributor documentation. REACH and halogen-free status not explicitly disclosed in retrieved sources.
