Texas Instruments LM3578AN

Overview

LM3578AN from Texas Instruments is a monolithic switching regulator controller IC featuring an internal NPN power transistor, dual comparator inputs (inverting and non-inverting), 1.0 V reference, and oscillator programmable up to 100 kHz via external capacitor. It supports buck, boost, and inverting DC-DC topologies with up to 750 mA output current and operates from 2 V to 40 V supply voltage. Used in industrial power supplies requiring stable mid-current regulation.

For engineers reviewing the LM3578AN datasheet, LM3578AN pinout, LM3578AN application, or LM3578AN equivalent, key selection criteria include its 0–90% duty cycle range, ground- or VIN-referenced current limit sensing, collector saturation voltage ≤0.9 V at 750 mA, and ambient temperature rating of 0°C to +70°C - critical for cost-sensitive non-automotive embedded power designs.

Technical Context

The LM3578AN implements a pulse-width modulation architecture with a dedicated oscillator section whose frequency is set by a single external timing capacitor (f_OSC = 8×10⁻⁵/C_T). Its comparator stage provides independent inverting and non-inverting inputs, each internally biased to 1.0 V, enabling direct feedback without external op-amps in inverting configurations.

Current limiting operates cycle-by-cycle using a 110 mV sense threshold referenced either to ground or VIN, with thermal shutdown and built-in protection against emitter output below ground (≤ −1 V). The output transistor is an NPN with separate collector and emitter terminals, supporting flexible external drive and saturation monitoring.

Key Specifications

Pinout & Package

LM3578AN is packaged in an 8-pin plastic DIP (Dual In-line Package), package number P0008E per TI documentation. Pin functions are validated per Figure 1 and Functional Diagram in SNVS767E.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switching regulator controller applications.

Compared with LM2578AN and MC34063AP, the LM3578AN offers optimal balance of commercial-temperature operation, dual-input comparator flexibility, and proven 750 mA drive - making it ideal for cost-sensitive embedded power where inverting capability or extended temperature is unnecessary.

Availability

LM3578AN is available at Aetrix Electronics and suitable for buck regulators, boost converters, inverting power supplies, and lamp flasher circuits requiring stable component supply and long-term commercial-grade availability.

Supply support for LM3578AN 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

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The LM3578A series belongs to TI's legacy switching regulator controller product line, designed specifically for discrete-based DC-DC conversion in cost-sensitive commercial applications where flexibility in topology and simplicity of implementation are prioritized.

FAQ

What is the maximum switching frequency supported by the LM3578AN?

The LM3578AN oscillator supports frequencies up to 100 kHz, with typical operation at 20 kHz (±4 kHz) as specified in the Electrical Characteristics table. The actual frequency is set by an external timing capacitor (CT) using f_OSC = 8×10⁻⁵/C_T. For the LM3578AN, the minimum guaranteed frequency is 16 kHz and maximum is 24 kHz under standard test conditions (T_J = 25°C, C_T = 3900 pF).

Does the LM3578AN support inverting regulator configurations?

Yes, the LM3578AN supports inverting regulator configurations natively due to its dual comparator inputs (pins 1 and 4), each internally biased to 1.0 V. This allows direct feedback from the negative output without external op-amps - as demonstrated in Figure 34 of the SNVS767E datasheet, where LM3578AN generates −15 V from +5 V with 300 mA output capability.

What is the absolute maximum emitter voltage for the LM3578AN?

The absolute maximum emitter voltage for the LM3578AN is −1 V relative to ground, as stated in the Absolute Maximum Ratings table. At junction temperatures ≥100°C, this limit tightens to −0.6 V. Exceeding these values risks unintended turn-on of the internal NPN transistor due to base-emitter clamping, potentially causing excessive power dissipation or latch-up.

Can the LM3578AN be synchronized to an external clock signal?

Yes, the LM3578AN can be synchronized to an external clock signal applied to the CT pin. TI's datasheet specifies that a pulse waveform with 1.5–2.0 V amplitude, minimum 2 µs pulse width, and capable of sourcing/sinking up to 500 µA per device can synchronize multiple LM3578AN units. External capacitors (C₁ through C_N) should be selected for ~20% lower free-running frequency than the sync signal.

How does the current limit function work on the LM3578AN?

The LM3578AN current limit senses voltage at pin 5 (CL) relative to either ground or VIN. A threshold of 110 mV (±30 mV) triggers cycle-by-cycle shutdown. When referenced to ground, a sense resistor between CL and ground converts load current to voltage; when referenced to VIN, the resistor connects between CL and VIN. The internal comparator disables the output transistor whenever the CL pin deviates 110 mV from its reference point.