Analog Devices Inc./Maxim Integrated MAX749CSA+T

Overview

The MAX749CSA+T from Maxim Integrated is a digitally adjustable negative-output LCD bias supply IC that generates programmable contrast voltages from +2V to +6V inputs, delivering up to –100V output in 64 discrete DAC steps. It drives external P-channel MOSFETs or PNP transistors using a flyback topology, features 60µA max quiescent current, 500kHz switching frequency, and retains DAC setpoint during shutdown - enabling precise, low-power contrast control in portable LCD systems.

For engineers reviewing the MAX749CSA+T datasheet, MAX749CSA+T pinout, MAX749CSA+T application, or MAX749CSA+T equivalent, this page delivers verified technical context, real-world design meaning for each specification, validated pin functions, confirmed alternative parts with functional distinctions, and supply-chain support details specific to the MAX749CSA+T.

Technical Context

The MAX749CSA+T implements a current-mode flyback controller with integrated 6-bit DAC and counter logic, combining pulse-skipping (PFM) at light loads and pulse-width modulation (PWM)-like behavior at heavy loads to maintain high efficiency across 5mA–40mA output ranges. Its internal current-sense comparator trips at 140mV (typ) across RSENSE, enforcing peak switch current limiting independent of input voltage.

Control is executed via two logic inputs: CTRL enables/disables operation and resets the DAC to mid-scale when ADJ is high; ADJ increments the DAC on rising edges. The FB pin accepts a single resistor to set full-scale output (–VOUT(MAX) = RFB × 20µA), while V+ powers both internal circuitry and external transistor gate/base drive.

Key Specifications

Pinout & Package

MAX749CSA+T is housed in an 8-pin SO (Small Outline) package, 3.9mm × 4.9mm body size, 1.27mm pitch, RoHS-compliant, with exposed pad not connected internally.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LCD bias supply applications.

Compared with MAX680CPA+ and LM2766MM/NOPB, the MAX749CSA+T uniquely combines wide output voltage range (–100V), flyback topology for high-efficiency high-voltage generation, and zero-software DAC retention - making it the only choice for dynamically adjustable, battery-powered STN/FSTN LCDs requiring >–24V bias.

Availability

MAX749CSA+T is available at Aetrix Electronics and suitable for notebook computers, portable data-collection terminals, and personal digital assistants requiring stable component supply with guaranteed long-term manufacturability and consistent electrical performance.

Supply support for MAX749CSA+T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in high-performance analog, mixed-signal, and power-management ICs for portable, industrial, and communications applications.

The MAX749CSA+T belongs to Maxim's LCD bias and portable power-management product line, designed specifically to replace discrete transistor-based bias supplies in space-constrained, battery-operated LCD systems.

FAQ

What is the maximum negative output voltage achievable with the MAX749CSA+T?

The MAX749CSA+T can generate full-scale output voltages of –100V or greater, determined by the external feedback resistor RFB using the formula –VOUT(MAX) = RFB × 20µA. For example, a 5MΩ RFB yields –100V full scale, and the internal 64-step DAC allows adjustment from –33V to –100V. The actual achievable voltage depends on external component ratings - particularly the breakdown voltage of the external transistor and diode.

Does the MAX749CSA+T require an external microcontroller to operate?

No, the MAX749CSA+T operates autonomously without a microcontroller. It supports three independent control methods: digital adjustment via ADJ/CTRL logic pins, analog adjustment using a potentiometer on the FB pin, or PWM-based control applied to FB. Its internal 6-bit counter and DAC retain state during shutdown, enabling standalone contrast control in systems lacking processing resources.

Can the MAX749CSA+T drive both P-channel MOSFETs and PNP transistors?

Yes, the MAX749CSA+T is explicitly designed to drive either an external P-channel MOSFET (e.g., SMD10P05L) or a PNP transistor (e.g., ZTX750). When using a MOSFET, connect DHI and DLOW together to the gate; when using a PNP, connect DHI to the base and DLOW to RBASE. The datasheet provides layout guidance and component selection tables for both configurations.

What is the purpose of the CS pin on the MAX749CSA+T?

The CS (Current Sense) pin on the MAX749CSA+T monitors the voltage drop across the external sense resistor RSENSE. When the voltage at CS falls 140mV (typical) below V+, the internal comparator disables the external switch to prevent overcurrent. This provides cycle-by-cycle current limiting independent of input voltage or temperature, protecting the external transistor and ensuring predictable peak current under all operating conditions.

How does the MAX749CSA+T achieve high efficiency across varying load conditions?

The MAX749CSA+T uses a hybrid control scheme: at light loads, it employs pulse-skipping (PFM) to minimize switching losses and reduce quiescent current to 60µA; at heavy loads, it transitions to quasi-PWM behavior with fixed-frequency current-mode control, maintaining >75% efficiency from 5mA to 40mA. This adaptive method, combined with 500kHz operation and low-R_DS(on) external switches, enables high efficiency across the full operating range without external compensation.