STMicroelectronics PM6644

Overview

PM6644 from STMicroelectronics is a 350 mA valley current limit step-down DC-DC regulator with integrated 3.3 V reference, operating from 4.5 V to 25 V input and delivering fixed 3.47 V or adjustable 0.9–8 V output. It uses constant-on-time (COT) control for fast transient response, supports programmable 200–600 kHz switching frequency via external resistor, and integrates latched OVP/UVP protection. It powers microcontroller cores in portable industrial systems requiring compact, efficient local regulation.

For engineers reviewing the PM6644 datasheet, PM6644 pinout, PM6644 application, or PM6644 equivalent, key selection criteria include its DFN10 3×3 mm package, dual-mode FB configuration (fixed vs. adjustable), valley-current-limited 350 mA capability, COT architecture benefits for dynamic load handling, and co-integrated REF3 3.3 V reference for auxiliary biasing.

Technical Context

The PM6644 implements a constant-on-time (COT) controller with voltage feed-forward, enabling near-constant switching frequency across line/load variations and sub-1 µs load transient recovery. Its valley current sensing triggers at 350 mA typical, with zero-crossing detection at 14–30 mA to prevent reverse inductor current.

It features independent EN control for full system sequencing, dual power paths for VCC (integrated 3.8 V generator when BYP < 2.4 V, or direct BYP switch-over when BYP > 3.2 V), and a dedicated 3.3 V linear regulator (REF3) with ±3% accuracy and 500 µV load regulation over 0–2 mA.

Key Specifications

Pinout & Package

Housed in a thermally enhanced DFN10 (3 mm × 3 mm, 0.5 mm pitch) package with exposed pad for ground connection and thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator with integrated reference applications.

Compared with TPS62231 and ADP2303, the PM6644 uniquely combines adjustable/fixed output modes, integrated REF3 reference, COT transient response, and DFN10 compactness - making it optimal for space-constrained, multi-rail embedded systems needing both power and precision bias.

Availability

PM6644 is available at Aetrix Electronics and suitable for networking power supply, portable applications, and microcontroller supply requiring stable component supply with long-term production continuity and RoHS-compliant packaging.

Supply support for PM6644 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The PM6644 belongs to ST's high-efficiency, small-footprint DC-DC regulator portfolio designed specifically for space- and performance-critical embedded systems requiring integrated functionality and robust protection.

FAQ

Can PM6644 operate with input voltage below 4.5 V?

No. The absolute minimum recommended input voltage is 4.5 V per Table 5. Operation below this risks failure to start, unstable regulation, or violation of the VCC generator's 6 V minimum requirement. Below 4.5 V, the device may not sustain oscillation or maintain REF3 accuracy, and is outside guaranteed operating conditions.

What is the purpose of the EXP PAD terminal?

It is the exposed thermal pad on the underside of the DFN10 package, electrically connected to GND. It must be soldered to a solid PCB ground plane to ensure thermal dissipation (R_thj-a = 45 °C/W) and electrical stability. Leaving it unconnected degrades thermal performance and may cause premature thermal shutdown.

How does the BYP pin affect VCC operation?

When BYP voltage exceeds 3.2 V, an internal MOSFET connects BYP directly to VCC, disabling the internal 3.8 V generator. When BYP falls below 2.4 V, the generator resumes supplying VCC. This allows flexible biasing: either use internal generation (BYP unconnected or grounded) or external 3.3–5 V supply (via BYP).

Is the REF3 output capable of sourcing >2 mA?

No. Electrical characteristics specify REF3 load regulation tested up to 2 mA, and typical output current capability is limited to 2 mA. Exceeding this risks output voltage droop beyond specification (±0.1 V), reduced accuracy, or thermal stress - external buffering is required for higher loads.