Texas Instruments LM2578AMX

Overview

LM2578AMX from Texas Instruments is a monolithic switching regulator controller IC featuring an integrated NPN output transistor, dual comparator inputs (inverting and non-inverting), internal 1.0 V reference, and oscillator programmable up to 100 kHz via single external capacitor. It supports buck, boost, and inverting DC-DC topologies with up to 750 mA output current, <0.9 V collector saturation voltage, and operates from 2 V to 40 V input supply - used in industrial power supplies and motor control circuits.

For engineers reviewing the LM2578AMX datasheet, LM2578AMX pinout, LM2578AMX application, or LM2578AMX equivalent, key selection considerations include its 90% max duty cycle, ground- or VIN-referenced current limit sensing, thermal shutdown, and compatibility with discontinuous/continuous conduction mode designs requiring stable 1.0 V reference accuracy and low-temperature-drift oscillator frequency.

Technical Context

The LM2578AMX implements a pulse-width modulation architecture with a unique dual-input comparator stage that provides independent 1.0 V references at both inverting and non-inverting pins, enabling direct feedback without external op-amps in inverting configurations. Its on-chip oscillator uses a single timing capacitor (CT) to set frequency from <1 Hz to 100 kHz, with built-in blanking for 90% duty cycle limiting.

It integrates a high-current NPN output transistor rated for 750 mA pulsed collector current, with separate collector and emitter terminals for flexible topology implementation. Current limiting operates cycle-by-cycle and can be referenced to either ground or VIN, with a nominal sense threshold of 110 mV and ±30 mV tolerance over temperature.

Key Specifications

Pinout & Package

LM2578AMX is packaged in an 8-pin SOIC (Small Outline Integrated Circuit) package per TI package code D0008A, with standard 1.27 mm pitch and gull-wing leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2578AMX, LM2575HVSX-5.0 trades topology flexibility for integration and ease-of-use in fixed-output buck applications, while UC3843N offers superior current-mode control at the cost of added external components and loss of dual-reference convenience.

Availability

LM2578AMX is available at Aetrix Electronics and suitable for industrial DC-DC power supplies, motor speed control circuits, lamp flasher systems, and inverting polarity converters requiring stable component supply and long-term manufacturability.

Supply support for LM2578AMX 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 leader specializing in analog, embedded processing, and power management technologies, with decades of experience in high-reliability industrial and automotive IC design.

The LM2578A product line was developed as a versatile, topology-agnostic switching regulator controller for cost-sensitive and space-constrained DC-DC applications where design flexibility and minimal external parts are critical.

FAQ

What is the maximum allowable emitter voltage below ground for LM2578AMX?

The LM2578AMX emitter output must not be driven more than −1 V below ground at TJ < 100°C; for junction temperatures ≥100°C, this limit tightens to −0.6 V. Exceeding this causes unintended turn-on of the internal NPN transistor due to base clamping, risking excessive power dissipation. For deeper negative swings, an external PNP transistor stage is required, as documented in TI's Application Note SNVS767E Figure 29.

Can LM2578AMX be used in synchronous rectification designs?

No, LM2578AMX does not support synchronous rectification. It features only a single NPN output transistor with collector and emitter terminals - no complementary gate drive outputs or timing control for external MOSFETs. Synchronous operation requires dedicated controllers like the TPS40200 or LM5116, which provide matched high-side/low-side gate drivers and dead-time control.

What is the minimum timing capacitor value for stable 50 kHz operation of LM2578AMX?

For 50 kHz oscillator frequency, LM2578AMX requires a timing capacitor of approximately 1820 pF, as confirmed in TI's typical application circuit (Figure 28). This value derives from the oscillator equation fOSC = 8×10⁻⁵/CT. Using significantly smaller capacitors risks frequency instability and increased jitter; larger values reduce frequency but improve noise immunity.

Does LM2578AMX include under-voltage lockout (UVLO) functionality?

Yes, LM2578AMX implements UVLO using external components: a zener diode and resistor network (Figure 21). When VIN drops below the zener breakdown voltage, the non-inverting input is pulled low relative to the inverting input, forcing the output transistor OFF. The IC itself has no internal UVLO threshold; proper external design is required to enable this protection.

How does the current limit function differ when referenced to VIN versus ground on LM2578AMX?

When current limit is referenced to VIN (Figure 16), the sense resistor connects between the current limit pin and VIN, enabling high-side sensing ideal for buck regulators. When referenced to ground (Figure 15), the resistor connects between the current limit pin and GND, supporting low-side sensing in boost/inverting topologies. The 110 mV threshold applies identically in both cases, but layout and noise immunity differ significantly.