Analog Devices Inc./Maxim Integrated MAX845ESA+TG55

Overview

MAX845ESA+TG55 from Maxim Integrated is an isolated transformer driver IC designed for space-constrained PCMCIA cards and low-profile DC-DC power supplies. It drives center-tapped transformers from a single +5V or +3.3V supply, delivers up to 750mW isolated output power, operates at ≥450kHz switching frequency, and features break-before-make N-channel power switches with 5µW shutdown current.

For engineers reviewing the MAX845ESA+TG55 datasheet, MAX845ESA+TG55 pinout, MAX845ESA+TG55 application, or MAX845ESA+TG55 equivalent, this page provides verified functional identity, confirmed SO-8 package mapping, validated 8-pin push-pull driver topology, real-world isolation use cases (RS-232/RS-485 interface power, medical data acquisition), and two documented alternative drivers with technical differentiation.

Technical Context

The MAX845ESA+TG55 integrates an RC oscillator driving a toggle flip-flop to generate complementary 50% duty-cycle square waves at half the oscillator frequency (≥450kHz min), directly controlling two ground-referenced N-channel power switches (D1/D2). Internal logic enforces 100ns break-before-make timing to prevent shoot-through.

It supports dual-frequency operation via the FS pin: ≥535kHz when FS = 0V, ≥725kHz when FS = VCC or open (internal pull-up). Shutdown is active-high on SD pin, disabling both oscillator and switches while drawing only 0.4µA typical supply current.

Key Specifications

Pinout & Package

MAX845ESA+TG55 is housed in an 8-pin SO (Small Outline) package, pin-compatible with the µMAX variant but with different thermal and mechanical characteristics. The SO package supports standard reflow soldering and offers 471mW continuous power dissipation at +70°C ambient.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar transformer driver applications.

Compared with MAX845ESA+TG55, MAX846ESA+ adds protection features without changing pinout or core functionality, while LM5017MM/NOPB shifts architecture to a controller-based solution requiring additional components and design effort for isolation.

Availability

MAX845ESA+TG55 is available at Aetrix Electronics and suitable for PCMCIA modem cards, isolated RS-232/RS-485 interfaces, and medical data acquisition systems requiring stable component supply and long-term industrial lifecycle support.

Supply support for MAX845ESA+TG55 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 industrial, medical, and communications applications.

The MAX845ESA+TG55 belongs to Maxim's isolated power product line, engineered specifically for ultra-thin, transformer-coupled DC-DC conversion in space-limited portable and embedded systems.

FAQ

What is the exact function of the MAX845ESA+TG55 in a circuit?

The MAX845ESA+TG55 is a dedicated isolated transformer driver IC that generates complementary push-pull waveforms to drive the primary of a center-tapped transformer. It does not regulate output voltage - regulation is achieved externally. Its core function is efficient, low-profile AC excitation of the transformer primary from a single 3.3V or 5V rail, enabling compact isolated DC power generation up to 750mW. The MAX845ESA+TG55 handles timing, switch control, and safety interlocks (break-before-make), offloading magnetics design complexity from the system engineer.

Does the MAX845ESA+TG55 support both 3.3V and 5V input supplies?

Yes, the MAX845ESA+TG55 is explicitly specified to operate from either a +3.3V or +5V supply, with ±10% tolerance. At 3.3V input, maximum output power is reduced to 500mW due to lower available energy per cycle and higher relative conduction losses. The device maintains the same switching frequency range and functional behavior across both rails - no configuration changes are needed. The MAX845ESA+TG55 datasheet confirms operation down to 3.0V minimum start-up voltage, ensuring reliable turn-on even under brownout conditions.

What is the purpose of the FS pin on the MAX845ESA+TG55?

The FS (Frequency Select) pin on the MAX845ESA+TG55 selects between two fixed switching frequencies: ≥535kHz when pulled low (0V), and ≥725kHz when tied to VCC or left open (internal pull-up). This allows designers to optimize transformer size versus EMI performance - higher frequency enables smaller magnetics but increases switching losses and radiated emissions. The MAX845ESA+TG55 uses this pin to adjust the fundamental operating point without altering external components, preserving layout simplicity while offering trade-off flexibility in final system tuning.

Can the MAX845ESA+TG55 be used for negative output voltages?

Yes, the MAX845ESA+TG55 supports negative isolated outputs by configuring the transformer secondary winding polarity and rectifier topology. For example, using a center-tapped secondary with a full-wave bridge (Figure 11b) or voltage doubler (Figure 11c) allows derivation of negative rails such as –5V or –12V - as demonstrated in the MAX176 ADC application (Figure 6). The MAX845ESA+TG55 itself remains agnostic to output polarity; it only drives the primary. Output sign is determined entirely by secondary winding direction and diode orientation, making it fully adaptable to bipolar or multi-rail isolated power architectures.

How does the shutdown feature work on the MAX845ESA+TG55?

The MAX845ESA+TG55 uses an active-high shutdown (SD) pin: driving SD to VCC disables the internal oscillator and both D1/D2 power switches, reducing supply current to just 0.4µA typical. SD must never be left floating - it has no internal default state. In normal operation, SD is grounded. The shutdown action is immediate (see "TIME FROM SHUTDOWN TO POWER-UP" waveform in datasheet Figure), with full recovery occurring within microseconds after SD returns low. This makes the MAX845ESA+TG55 suitable for dynamic power gating in battery-powered or energy-conscious systems where rapid on/off cycling is required.