MAX138CMH - 3.5-Digit ADC with LCD Drivers | Analog Devices
MPN： MAX138CMH ✓ 啟用中MAX138CMH 概覽
A dual-slope ADC is a type of integrating analog-to-digital converter that measures input voltage by integrating it over a fixed interval and comparing the result with a reference ramp. It belongs to the wider ADC hierarchy and is especially useful when a moderate-resolution digital measurement is required alongside direct display drive. The MAX138 combines that conversion function with circuitry intended to simplify digital panel-meter and laboratory-instrument designs.
The MAX138's headline features are its 3.5-digit resolution, single +2.5 V to +7 V operating range, and integrated direct LED drivers. Its reference and charge-pump functions reduce the number of external support components required in a typical measurement circuit. Bipolar input capability is valuable for sensing voltages around ground, while the integrated display drivers provide a direct path to common-anode LED display segments.
The MAX138 operating circuits are similar to those of the ICL7136, but the MAX138 adds an internal oscillator and uses an external charge-pump capacitor connected to pins 38 and 40. This integration supports autonomous conversion timing without requiring a separate clock source. The device is identified as a dual-slope converter and is designed for panel-meter-style measurement rather than high-speed waveform acquisition.
Typical uses include digital panel meters, laboratory test equipment, process-monitoring instruments, temperature measurement systems, and low-speed sensor interfaces. The bipolar input capability allows negative voltages to be measured within the instrument's input network, while the LED drivers simplify displays showing three and a half digits.
For PCB design, preserve the manufacturer's recommended charge-pump and reference capacitors, confirm input-network limits against the selected measurement range, and route display outputs away from sensitive analog inputs. Because this is a low-speed integrating converter, application filtering and input settling time are as important as raw conversion speed.
This page summarizes the MAX138CMH's verified construction and operating characteristics, organizes its selection criteria against available family variants, and highlights practical design considerations for bipolar panel-meter and display applications.
直接替換替代品，適用於 MAX138CMH — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
MAX138CMH+
✅ 直接替換📋 參考替代品（不在目錄中）
MAX138CMH+D
✅ 直接替換📋 參考替代品（不在目錄中）
MAX138CMH 最大額定值與電氣特性
| ADC Type | 3.5-digit dual-slope ADC |
| Supply Voltage Range | +2.5 V to +7 V |
| Input Type | Bipolar input |
| Reference | Internal reference source |
| Charge-Pump Circuit | Internal charge pump with external capacitor at pins 38 and 40 |
| Display Driver | Direct LED driver |
| Oscillator | Internal oscillator |
| Package Type | 44-pin MQFP |
| Package Dimensions | 10 mm x 10 mm |
| Terminal Count | 44 terminals |
| Lead Form | Gull wing |
| Package Shape | Square |
| Temperature Grade | Commercial |
| 解析度 | 3.5 digits |
MAX138CMH square 腳位配置指南
MAX138CMH（square 封裝）的腳位配置。 此類比元件具有輸入、輸出與電源腳位。偏移歸零、補償與致能腳位配置請參閱製造商資料表。適用於訊號調理與放大器電路。
無詳細腳位定義資料： MAX138CMH.
請參閱 資料表 以查看完整腳位配置。
典型應用
MAX138CMH 適用於 6 應用s: Digital Panel Meters, Laboratory Test Instruments, Temperature Measurement Systems, Industrial Process Monitoring, Low-Speed Sensor Interfaces, Power and Equipment Monitoring.
Digital Panel Meters
The MAX138CMH fits digital panel meters because it combines a 3.5-digit dual-slope ADC with an internal reference, internal oscillator, and direct LED drivers. A single +2.5 V to +7 V supply simplifies the power architecture, while bipolar input support accommodates measurements around ground. The direct display-driver outputs reduce the need for separate segment-driver circuitry, although display polarity and drive-current requirements must be checked against the selected LED module before layout.
推薦
Laboratory Test Instruments
The MAX138CMH is appropriate for slow, precision-oriented laboratory displays where a 3.5-digit result must be presented locally rather than streamed rapidly to a computer. Its dual-slope conversion, integrated reference, and internal oscillator provide the basic measurement functions in one device. Bipolar input capability is useful for bidirectional probes and sensor bridges, but the input divider, protection network, grounding, and calibration procedure remain critical to achieving useful measurement accuracy.
推薦
Temperature Measurement Systems
A MAX138CMH-based temperature instrument can convert a conditioned thermocouple, RTD, or thermistor signal into a three-and-a-half-digit display value. The device accepts bipolar inputs, which is convenient when the measurement is referenced around ground, while its integrated reference supports repeatable display-only measurements. System accuracy will usually be limited by the sensor, input conditioning, cold-junction compensation, and calibration rather than by the converter's display resolution.
推薦
Industrial Process Monitoring
The MAX138CMH can serve as the local display converter in industrial process-monitoring equipment that reports a slow-moving voltage, current, pressure, or position value. Its internal reference and internal oscillator reduce external timing and reference circuitry, and the direct LED drivers suit front-panel indication. The +2.5 V to +7 V operating range supports low-voltage systems, but industrial deployments still require appropriate input protection, isolation or grounding decisions, and environmental qualification for the assembled instrument.
推薦
Low-Speed Sensor Interfaces
The MAX138CMH is suitable for slow sensor interfaces whose output changes more slowly than the dual-slope measurement cycle. The 3.5-digit converter can present the value directly on an LED display without requiring a separate display driver. Its bipolar input capability is valuable for sensors with positive and negative excursions, while the internal reference and oscillator simplify standalone instrumentation. Designers should verify conversion timing and input settling against the sensor's response characteristics.
推薦
Power and Equipment Monitoring
The MAX138CMH can display a single supply, load, or rail voltage in compact power-monitoring equipment. Its bipolar input capability helps with measurements that include negative rails, and the +2.5 V to +7 V supply range is compatible with low-voltage monitoring systems. Direct LED drivers allow the measured value to be shown locally, reducing controller overhead. For safety-critical measurements, add appropriate input attenuation, fusing, surge protection, and isolation rather than relying on the ADC alone.
推薦
推薦產品摘要
工程參考資料，適用於 MAX138CMH — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | MAX138CMH+ | MAX138CMH+D |
|---|---|---|---|
| Package | 44-MQFP (10 mm x 10 mm) | 44-MQFP (10 mm x 10 mm) - same | 44-MQFP (10 mm x 10 mm) - same |
| Brand | Analog Devices | Analog Devices | Analog Devices |
| ADC Resolution | 3.5 digits | 3.5 digits | 3.5 digits |
| ADC Architecture | Dual-slope | Dual-slope | Dual-slope |
| Supply Voltage Range | +2.5 V to +7 V | +2.5 V to +7 V | +2.5 V to +7 V |
| Input Type | Bipolar | Bipolar | Bipolar |
| Reference Source | Internal | Internal | Internal |
| Display Driver | Direct LED driver | Direct LED driver | Direct LED driver |
| Oscillator | Internal | Internal | Internal |
| Charge-Pump Capacitor Connections | Pins 38 and 40 | Pins 38 and 40 | Pins 38 and 40 |
主要差異化特點
- Integrated display and measurement functions (對比MAX138CMH+)
- Single-supply bipolar measurement capability (對比MAX138CMH+D)
- Directly integrated charge-pump timing support (對比MAX138CMH+)
設計說明
Place the external charge-pump capacitor at pins 38 and 40 using the shortest practical traces and the capacitor value specified by Analog Devices. Keep this network away from LED-driver outputs and sensitive input traces because display switching can introduce ground and supply disturbances. Match the MQFP land pattern to the manufacturer's package drawing and verify pin 1 orientation against the PCB footprint before assembly.
Design the bipolar input network so the source impedance, protection components, and filtering capacitors agree with the MAX138 conversion cycle and acquisition timing. A high-impedance source combined with excessive filter capacitance can prevent settling between conversions. Use a low-noise reference path, guard the analog input from LED-driver currents, and validate accuracy across the intended input range rather than relying only on display resolution.
Operate the MAX138CMH from a single +2.5 V to +7 V source while observing the absolute limits and output-driver requirements in the manufacturer data sheet. Provide local input capacitance close to the supply pins and separate sensitive analog return paths from display-driver currents. Check LED segment current, supply ripple, and ground bounce together because display loading can create measurement error even when the ADC reference is stable.
Do not treat the 3.5-digit display as the complete accuracy specification. Overall measurement accuracy also depends on the internal-reference behavior, input scaling, calibration, sensor error, and layout. Confirm the LED display's common-anode or common-cathode arrangement and segment mapping before connecting direct driver outputs. Also confirm the exact ordering suffix and temperature grade before releasing the BOM.
合規資訊
The MAX138 is a commercial-grade ADC. The verified product information does not state RoHS, REACH, lead-free, halogen-free, or conflict-minerals status; AEC-Q100 is not applicable to this non-automotive device.
