Texas Instruments LM3100MHX

Overview

LM3100MHX from Texas Instruments is a synchronous step-down DC-DC regulator IC integrating dual 40 V N-channel MOSFETs, delivering 1.5 A output current with 0.8 V ±1.5% reference voltage, operating across 4.5 V to 36 V input range, and supporting programmable switching frequency up to 1 MHz - used in industrial control power rails and automotive body electronics.

For engineers reviewing the LM3100MHX datasheet, LM3100MHX pinout, LM3100MHX application, or LM3100MHX equivalent, key selection considerations include its Constant ON-Time (COT) control architecture, valley current limit at 1.9 A, integrated VCC LDO, soft-start via external capacitor, and thermal shutdown at 165°C - all implemented in an HTSSOP-20 package with exposed thermal pad.

Technical Context

The LM3100MHX employs a Constant ON-Time (COT) regulation scheme where high-side switch on-time is inversely proportional to VIN and set by RON resistor, enabling near-constant switching frequency across line/load variations without loop compensation. Its valley current limit detects recirculating inductor current through the synchronous low-side MOSFET, triggering inhibition of the next on-pulse when exceeding 1.9 A.

Regulation relies on a precision 0.8 V internal reference compared against FB pin voltage; over-voltage protection activates at 0.92 V to terminate on-time immediately. The integrated 6 V start-up regulator (VCC) powers internal circuitry and gate drivers, requiring ≥680 nF bypass capacitance and exhibiting 3.75 V UVLO with 130 mV hysteresis.

Key Specifications

Pinout & Package

LM3100MHX is housed in a thermally enhanced HTSSOP-20 package (6.50 mm × 4.40 mm) with exposed power pad (EP) tied to GND for improved thermal performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck regulator applications.

Compared with LM22678TJE-ADJ/NOPB and TPS54302DDCR, the LM3100MHX uniquely balances wide-input capability (4.5–36 V), COT simplicity, and 1.5 A output in a thermally optimized HTSSOP-20 - making it optimal for industrial and automotive POL where input transients and thermal reliability are critical.

Availability

LM3100MHX is available at Aetrix Electronics and suitable for industrial control power supplies, automotive body electronics, and embedded system core voltage generation requiring stable component supply and long-term manufacturability.

Supply support for LM3100MHX 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 specializing in analog, embedded processing, and power management ICs, with decades of leadership in high-reliability power conversion solutions.

The LM3100MHX belongs to TI's Simple Switcher® family of integrated DC-DC regulators, designed specifically for cost-sensitive, space-constrained industrial and automotive applications demanding robust input voltage handling and minimal external components.

FAQ

What is the minimum input voltage required for stable operation of the LM3100MHX?

The LM3100MHX requires a minimum input voltage of ≈4.0 V to maintain stable operation. This is determined by the VCC regulator's dropout voltage and its 3.75 V under-voltage lockout (UVLO) threshold. Below 4.0 V, the VCC UVLO activates and disables the buck switch, preventing regulation. The datasheet specifies 4.5 V as the recommended minimum operating voltage to ensure margin across temperature and tolerance.

How does the LM3100MHX achieve stability without external compensation components?

The LM3100MHX uses a Constant ON-Time (COT) control architecture that inherently avoids phase-margin instability issues. It compares FB voltage directly to a 0.8 V internal reference and triggers fixed-duration on-pulses - eliminating the need for traditional Type II/III compensation networks. Stability is maintained even with zero-ESR ceramic output capacitors because the control loop does not depend on capacitor ESR for pole-zero placement.

Can the LM3100MHX be used with an output voltage lower than 0.8 V?

No, the LM3100MHX cannot regulate below 0.8 V. Its internal reference is fixed at 0.8 V ±1.5%, and the feedback comparator only functions correctly when the FB pin voltage equals this reference. For VOUT = 0.8 V, FB is connected directly to the output; lower voltages would violate the regulation condition and cause loss of control. External resistive dividers can only increase, not decrease, the effective reference.

What is the purpose of the TST pin on the LM3100MHX, and how should it be connected?

The TST (Test) pin on the LM3100MHX forces the device into test mode when pulled high; it must be connected to GND for normal operation. Leaving TST floating or applying voltage above GND may result in undefined behavior or failure to regulate. The datasheet explicitly states that TST must be grounded - no pull-up or series resistor is permitted in functional designs.

How is the switching frequency programmed on the LM3100MHX?

The LM3100MHX switching frequency is programmed using an external resistor (RON) connected between VIN and the RON pin. The on-time t_ON is calculated as t_ON = (1.3 × 10⁻¹⁰) × RON / V_IN, and frequency is derived from t_ON and off-time (260 ns minimum). For example, with RON = 50 kΩ and VIN = 12 V, t_ON ≈ 542 ns and F_SW ≈ 850 kHz. RON must be selected so t_ON ≥ 200 ns at maximum VIN to ensure proper current limit operation.