MAX138EQH - 3.5-Digit LCD ADC with Reference | Analog Devices
MPN: MAX138EQH ✓ ActiveMAX138EQH Overview
An analog-to-digital converter, or ADC, converts an analog input voltage into a digital code for measurement, display, control, or data processing. The MAX138EQH belongs to the dual-slope ADC family and resolves approximately 3.5 decimal digits. A 3.5-digit display commonly represents a full-scale value from 0000 through 1999, allowing the converter to resolve one count in a 2000-count measurement range. This resolution is well suited to digital panel meters, laboratory instruments, and process-monitoring equipment where direct numerical display is more useful than a high-resolution waveform representation.
Integrated features reduce the number of surrounding components in a meter design. The on-chip reference establishes the conversion reference, while the charge-pump circuit supports the specified single-supply operating range. Direct LED drivers allow the converter to drive display elements without a separate display-driver IC. According to the Analog Devices product documentation, the MAX138 family also accepts bipolar input signals, allowing a frontend to measure positive or negative quantities relative to a defined common reference.
The dual-slope conversion architecture integrates the input over a fixed measurement interval and compares the result against a reference ramp. This approach is well matched to slowly changing measurements such as temperature, pressure, level, weight, and laboratory process variables. Its practical benefits include effective rejection of periodic interference, straightforward integration into digital meters, and a direct path to LED-segment display outputs. These characteristics are more valuable than maximum conversion speed for this class of instrumentation.
Typical uses include bench-top digital multimeters, temperature controllers, panel meters, laboratory displays, industrial process indicators, and compact weighing or dispensing equipment. The MAX138EQH is particularly appropriate when a readable three-and-a-half-digit result, bipolar input capability, and direct display excitation are desired in one IC. Designers should still verify front-panel drive requirements, reference accuracy, input filtering, and timing behavior against the manufacturer datasheet before laying out the PCB.
A key design consideration is that the converter, reference, display outputs, and power supply share a compact analog and mixed-signal layout. Keep the input and reference paths compact, maintain stable supply decoupling near the device, and route display-drive currents away from sensitive measurement nodes. Validate the complete meter accuracy with the intended transducers, wiring, grounding, and display rather than relying only on nominal converter resolution.
This product page combines the Analog Devices MAX138 family specifications with practical guidance for LCD meter design, drop-in family alternatives, package-aware comparison, and application-oriented selection. It highlights where the integrated reference, charge pump, bipolar-input capability, and LED drivers simplify a design while distinguishing it from unrelated converter families that use different packages, interfaces, or measurement architectures.
Drop-in alternatives for MAX138EQH — 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 MAX138EQH (same form factor and footprint) — differing in Charge Pump, Package.
MAX138EQH+D
✅ Drop-In📋 Reference alternative (not in catalog)
MAX138CQH+D
✅ Drop-In📋 Reference alternative (not in catalog)
MAX138CQH+TD
✅ Drop-In📋 Reference alternative (not in catalog)
MAX138CMH+C10166
✅ Drop-In📋 Reference alternative (not in catalog)
MAX138EPL+
✅ Drop-In ⚠️ Specs UnverifiedContact for price
View Datasheet →MAX138EQH Maximum Ratings & Electrical Characteristics
| ADC Type | Dual-slope, 3.5-digit ADC |
| Number of Channels | 1 channel |
| Resolution | 3.5 decimal digits |
| Supply Voltage Range | +2.5 V to +7 V |
| Input Signal Capability | Bipolar input |
| Internal Reference | Integrated |
| Charge Pump | Integrated |
| Display Driver | Direct LED drivers |
| Data Interface | Serial |
| Package | 44-pin PLCC, J-lead, 16.59 mm x 16.59 mm |
| Operating Temperature | -40 °C to +85 °C |
| Packaging | Tube |
| Production Status | Production |
MAX138EQH 44-pin plcc, j-lead, 16.59 mm x 16.59 mm Pin Configuration Guide
Pin configuration for MAX138EQH (44-pin plcc, j-lead, 16.59 mm x 16.59 mm package). This analog component features input, output, and power supply pins. Refer to the manufacturer datasheet for offset null, compensation, and enable pin configurations. Ideal for signal conditioning and amplifier circuits.
No detailed pinout data available for MAX138EQH.
Refer to the datasheet for full pin configuration.
Typical Applications
MAX138EQH is suitable for 6 applications: Digital Panel Meters, Temperature Measurement Instruments, Laboratory Digital Instruments, Industrial Process Indicators, Bench-Top Digital Multimeter, Load and Balance Displays.
Digital Panel Meters
The MAX138EQH fits digital panel meters because its 3.5-digit dual-slope ADC, internal reference, and direct LED drivers combine measurement and display functions in one IC. The single +2.5 V to +7 V supply simplifies low-voltage instrument design, while bipolar-input capability supports meters that display both positive and negative readings. In a panel-meter implementation, the sensor signal is conditioned into the permitted input range, and the converter drives the segmented display directly. The architecture is most appropriate for slow-changing measurements where readable resolution is more important than rapid conversion throughput.
Recommended
Temperature Measurement Instruments
The MAX138EQH is suitable for thermocouple, RTD, or resistance-based temperature instruments when the front end converts the sensed temperature into a bipolar voltage. Its 3.5-digit resolution provides a practical numerical display range, and the integrated reference, charge pump, and LED drivers reduce the number of separate support components. The dual-slope ADC is particularly suitable for thermal signals that change relatively slowly. Front-end amplifier gain, input protection, and sensor wiring must be designed so the complete instrument meets its intended accuracy rather than relying on converter resolution alone.
Recommended
Laboratory Digital Instruments
A laboratory display instrument can use the MAX138EQH when a direct, readable three-and-a-half-digit measurement is preferable to a high-speed converter output. The device accepts bipolar inputs and includes an internal reference, which simplifies the central signal chain around slowly varying laboratory quantities. Its +2.5 V to +7 V operating range allows use with common low-voltage regulated supplies. Designers should add suitable input attenuation, filtering, calibration, and protection while verifying reference accuracy, noise performance, and display-drive limits in the manufacturer datasheet.
Recommended
Industrial Process Indicators
The MAX138EQH supports industrial process indicators for pressure, flow, level, or other slowly varying process variables. Its dual-slope conversion architecture is appropriate when the process signal changes gradually, and the integrated reference and display drivers help create a compact front panel. Bipolar input capability accommodates positive and negative readings around the process zero point. The measurement conditioner should include electrical isolation or protection where required, while the PCB should keep high-current display and actuator wiring away from sensitive analog nodes.
Recommended
Bench-Top Digital Multimeter
The MAX138EQH can serve as the display converter in a bench-top digital multimeter designed around a three-and-a-half-digit numerical indication. It combines a one-channel dual-slope ADC with an internal reference, charge pump, and LED drivers, while accepting bipolar inputs for resistance, voltage, or temperature-derived measurements. The 44-pin PLCC package is relatively large compared with modern surface-mount ADC packages, but it remains practical for leaded legacy-style and industrial instrument designs. Input switching, protection, calibration, and safety barriers remain functions of the complete meter rather than the converter alone.
Recommended
Load and Balance Displays
The MAX138EQH is applicable to compact load-cell indicators, weighing systems, and balance displays that need a straightforward numeric result rather than a rapid conversion stream. The 3.5-digit resolution and integrated LED drivers suit a basic commercial display, while the internal reference helps simplify the converter subsystem. Mechanical shock, sensor lead noise, common-mode voltage, and input grounding often determine real weighing accuracy. Use the device within its electrical limits, retain the dual-slope advantage for slowly varying forces, and validate calibration across the full sensor and load range.
Recommended
Recommended Products Summary
Engineering reference data for MAX138EQH — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MAX138EQH+D | MAX138CQH+D | MAX138CQH+TD | MAX138CMH+C10166 | MAX138EPL+ |
|---|---|---|---|---|---|---|
| Package | 44-pin PLCC, J-lead | 44-pin PLCC | 44-pin PLCC | 44-pin PLCC | 44-pin PLCC | 44-pin PLCC |
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| ADC Architecture | Dual-slope ADC | Dual-slope ADC | Dual-slope ADC | Dual-slope ADC | Dual-slope ADC | Dual-slope ADC |
| Resolution | 3.5 decimal digits | 3.5 decimal digits | 3.5 decimal digits | 3.5 decimal digits | 3.5 decimal digits | 3.5 decimal digits |
| Number of Channels | 1 channel | 1 channel | 1 channel | 1 channel | 1 channel | 1 channel |
| Supply Voltage Range | +2.5 V to +7 V | +2.5 V to +7 V | +2.5 V to +7 V | +2.5 V to +7 V | +2.5 V to +7 V | +2.5 V to +7 V |
| Input Capability | Bipolar input | Bipolar input | Bipolar input | Bipolar input | Bipolar input | Bipolar input |
| Integrated Features | Reference, charge pump, direct LED drivers | Reference, charge pump, direct LED drivers | Reference, charge pump, direct LED drivers | Reference, charge pump, direct LED drivers | Reference, charge pump, direct LED drivers | Reference, charge pump, direct LED drivers |
| Interface | Serial | Serial | Serial | Serial | Serial | Serial |
Key Differentiators
- Integrated display-meter signal chain (vs MAX138EQH+D)
- Single-supply operation with internal charge pump (vs MAX138CQH+D)
- Direct LED output integration (vs MAX138CMH+C10166)
- Bipolar measurement capability (vs MAX138CQH+TD)
Design Notes
Place the input-conditioning network, reference bypass, and supply-decoupling components close to the corresponding MAX138EQH pins. Keep the analog input traces short and separate them from display-drive and external switching currents. A compact, ground-referenced analog region reduces susceptibility to errors that can appear as unstable meter readings even when the converter itself is operating correctly.
Use a low-noise, low-drift reference arrangement and route the analog node away from the direct LED-drive outputs. Display multiplexing and external relays can inject transient current into sensitive measurement paths. If the input source has high source impedance, include suitable filtering and account for settling time in the dual-slope measurement cycle. Confirm all input and reference limits in the manufacturer datasheet before setting the gain network.
Do not assume that a related MAX138 suffix is automatically interchangeable. Verify the ordering table, temperature grade, package, pin assignment, and lifecycle configuration for MAX138EQH+D, MAX138CQH+D, or other family members before replacing an installed device. Also avoid driving display outputs beyond their specified limits and provide suitable protection for external sensor wiring, where the measurement system can experience transients or ground-potential differences.
Use a continuous ground plane beneath and around the device, but partition high-current display and switching paths from the measurement-return path. Decouple the +2.5 V to +7 V supply close to the IC and control the amount of copper attached to sensitive signal nodes if leakage or temperature gradients affect accuracy. Review the manufacturer's recommended PCB layout and test setup before releasing a multi-channel or high-precision meter design.
Compliance Information
The MAX138 family is listed as production by Analog Devices, but explicit RoHS, REACH, lead-free, halogen-free, and conflict-minerals declarations are not present in the available product information. AEC-Q100 is not applicable to this general-purpose meter ADC.
