Texas Instruments LM3578AMX

Overview

LM3578AMX from Texas Instruments is a monolithic switching regulator controller IC featuring an internal 1.0V reference, dual comparator inputs (inverting and non-inverting), 750 mA output transistor with <0.9V collector saturation voltage, and oscillator frequency adjustable up to 100 kHz via external capacitor. It supports buck, boost, and inverting DC-DC topologies in industrial power supplies requiring stable mid-temperature operation.

For engineers reviewing the LM3578AMX datasheet, LM3578AMX pinout, LM3578AMX application, or LM3578AMX equivalent, key selection criteria include its 0°C to +70°C ambient operating range, ground- or VIN-referenced current limit sensing, duty cycle up to 90%, and compatibility with standard SOIC-8 PCB layouts.

Technical Context

The LM3578AMX integrates a precision 1.0V reference into both comparator inputs, enabling direct feedback without external op-amps in inverting configurations. Its oscillator uses a single external capacitor (CT) to set frequency from <1 Hz to 100 kHz, with built-in blanking for 90% max duty cycle enforcement.

It drives an NPN output transistor capable of 750 mA pulsed 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

LM3578AMX is housed in an 8-pin SOIC package (Package Number D0008A), with thermal performance rated at 150°C/W junction-to-ambient.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2578AMX, LM2578AMX extends temperature capability without layout change, while MC34063AP reduces feature set and increases design effort for inverting or precision reference applications.

Availability

LM3578AMX is available at Aetrix Electronics and suitable for industrial DC-DC power supplies, automotive auxiliary modules, and motor control drivers requiring stable component supply across commercial temperature grades.

Supply support for LM3578AMX 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 legacy in power conversion ICs.

The LM3578A product line delivers rugged, topology-flexible switching regulator controllers optimized for cost-sensitive, medium-power DC-DC applications in commercial and light-industrial environments.

FAQ

What is the maximum allowable junction temperature for LM3578AMX?

The LM3578AMX has a maximum junction temperature of +125°C, as specified in its Operating Ratings table. This limit applies across its full 0°C to +70°C ambient operating range. Exceeding this temperature risks permanent damage or parametric shift. Thermal design must account for the SOIC-8 package's 150°C/W junction-to-ambient thermal resistance and ensure adequate copper area or airflow to maintain TJ ≤125°C under worst-case load and ambient conditions. The LM3578AMX does not include thermal shutdown circuitry, so external thermal monitoring or derating is recommended.

Can LM3578AMX be used in an inverting regulator configuration without external op-amps?

Yes, the LM3578AMX supports inverting regulator configurations without external op-amps due to its unique dual comparator input stage with internal 1.0 V references on both pins. This allows direct feedback from the negative output rail to the inverting input while maintaining correct polarity relationship. Figure 34 in the TI datasheet SNVS767E demonstrates a working −15 V from +5 V design using only passive components. The internal level-shift accuracy of ≤1.0% ensures tight output regulation without added gain stages.

What is the minimum timing capacitor value needed to achieve 50 kHz oscillator frequency with LM3578AMX?

Using the oscillator equation fOSC = 8×10⁻⁵/CT, a 50 kHz frequency requires CT = 8×10⁻⁵ / 50,000 = 1600 pF. The LM3578AMX datasheet confirms 1820 pF (Figure 28) as the standard value for 50 kHz operation, aligning with this calculation. A 1600 pF capacitor is acceptable, but 1820 pF is preferred for margin against process variation and temperature drift. Capacitor tolerance and dielectric stability (e.g., C0G/NP0) directly impact frequency accuracy-±5% tolerance yields ±5% frequency variation.

How does the current limit function differ when referenced to VIN versus ground on LM3578AMX?

When referenced to VIN, the LM3578AMX current limit activates if the Current Limit pin voltage falls 110 mV below VIN; when referenced to ground, it triggers if the pin rises 110 mV above ground. This dual-reference capability allows optimal noise rejection: ground-referencing suits low-side sensing (e.g., shunt at GND), while VIN-referencing enables high-side sensing (e.g., shunt at input) to avoid ground loop interference. The internal comparators are hardwired for these two thresholds-no configuration bits or external resistors are needed to select mode.

Is LM3578AMX pin-compatible with LM2578AMX?

Yes, LM3578AMX is fully pin-compatible with LM2578AMX in the SOIC-8 package (D0008A). Both share identical pin functions, electrical specifications, and timing behavior. The only difference is the ambient temperature rating: LM3578AMX is rated for 0°C to +70°C, while LM2578AMX extends to −40°C to +85°C. No PCB layout changes are required when substituting LM3578AMX for LM2578AMX in commercial-temperature applications, though thermal derating may apply near the upper ambient limit.