Texas Instruments LM3670MF-1.875

Overview

LM3670MF-1.875 from Texas Instruments is a fixed-output synchronous step-down DC-DC converter optimized for ultralow-voltage circuits powered by single Li-Ion or three-cell NiMH/NiCd batteries. It delivers up to 350 mA load current with 1.875 V output, 1-MHz fixed PWM switching frequency, 15 µA typical quiescent current, and operates across 2.5 V to 5.5 V input range - used in mobile phone core logic power rails.

For engineers reviewing the LM3670MF-1.875 datasheet, LM3670MF-1.875 pinout, LM3670MF-1.875 application, or LM3670MF-1.875 equivalent, key selection considerations include dropout behavior at light load, PFM/PWM mode transition thresholds, internal synchronous rectifier efficiency at sub-2V outputs, and SOT-23-5 layout constraints for portable battery-powered designs.

Technical Context

The LM3670MF-1.875 implements voltage-mode control with input feed-forward compensation and automatic seamless transition between PWM (≥70 mA) and hysteretic PFM (<70 mA) modes. Its internal PFET/NFET synchronous rectifier pair enables high efficiency (90–95% at 1–100 mA) and 100% duty-cycle low-dropout operation down to VIN = VOUT + ILOAD × (RDSON(P) + RINDUCTOR).

Functional blocks include a 0.5 V internal reference, soft-start ramp generator, undervoltage lockout (2.4 V), cycle-by-cycle current limiting (620 mA typ), thermal shutdown, and zero-current detection for PFM mode termination. The FB pin connects directly to VOUT in fixed-output variants, eliminating external resistor dividers.

Key Specifications

Pinout & Package

The LM3670MF-1.875 is housed in a 5-pin SOT-23 package (2.90 mm × 1.60 mm body size), optimized for space-constrained portable PCB layouts with minimal thermal mass.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down DC-DC converter applications.

Compared with TPS62231DRVR and AP63205WU-18, the LM3670MF-1.875 provides the only industry-standard 1.875 V fixed output option in SOT-23-5, retains proven PFM/PWM auto-switching at ultra-low IQ, and offers superior dropout performance below 2.7 V - making it irreplaceable in legacy portable platforms requiring precise voltage alignment with ASIC core specifications.

Availability

LM3670MF-1.875 is available at Aetrix Electronics and suitable for mobile phones, handheld medical instruments, PDAs, and wearable fitness trackers requiring stable component supply across multi-year production cycles.

Supply support for LM3670MF-1.875 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, specializing in analog, embedded processing, and power management technologies for industrial, automotive, and consumer markets.

The LM3670 product line was designed specifically for ultralow-voltage, battery-powered portable electronics - delivering high efficiency, minimal external component count, and robust protection features in sub-3 mm² footprints.

FAQ

What is the minimum input voltage required for LM3670MF-1.875 to regulate 1.875 V at 350 mA?

The minimum input voltage for LM3670MF-1.875 to sustain 1.875 V output at 350 mA is calculated as VIN(MIN) = VOUT + ILOAD × (RDSON(P) + RINDUCTOR). With max RDSON(P) = 690 mΩ and typical inductor DCR < 0.3 Ω, VIN(MIN) ≈ 1.875 V + 0.35 A × 0.99 Ω = 2.22 V - but per datasheet, guaranteed operation starts at 2.5 V due to UVLO threshold and margin requirements. LM3670MF-1.875 enters 100% duty-cycle mode below 2.7 V input.

Does LM3670MF-1.875 require external feedback resistors to set its output voltage?

No, LM3670MF-1.875 does not require external feedback resistors. It is a fixed-output variant with internal resistor divider network trimmed to deliver 1.875 V; the FB pin connects directly to VOUT in application circuits. This eliminates resistor tolerance errors and saves PCB area - a key advantage over adjustable buck converters like LM3670SD-ADJ. LM3670MF-1.875 simplifies design by removing tuning complexity.

How does LM3670MF-1.875 behave during load transients from 1 mA to 300 mA?

LM3670MF-1.875 automatically transitions from PFM to PWM mode within 32 clock cycles (~32 µs at 1 MHz) when load increases past ~70 mA. Output voltage deviation is limited to ±1.6% of nominal (±30 mV) due to fast error amplifier response and internal compensation. Recovery time to within 1% of 1.875 V is <100 µs, verified in Figure 11 and 12 of the SNVS250F datasheet. LM3670MF-1.875 maintains regulation without external loop compensation.

Can LM3670MF-1.875 be used with a 2.2 µH inductor instead of the recommended 4.7 µH or 10 µH?

Using a 2.2 µH inductor with LM3670MF-1.875 is not recommended. At 1-MHz switching, 2.2 µH yields excessive peak-to-peak inductor current ripple (>400 mA), risking saturation, reduced efficiency, and potential current-limit triggering. The datasheet specifies 4.7 µH (for low-profile) or 10 µH (for lower ripple) with ≥800 mA saturation rating. LM3670MF-1.875's control loop is optimized for 4.7–10 µH; deviating compromises stability and transient response.

What thermal derating applies to LM3670MF-1.875 at 350 mA continuous load on a standard 2-layer PCB?

On a standard 2-layer FR-4 PCB with 1-in² copper pour under the LM3670MF-1.875 SOT-23-5 package, junction temperature rise is calculated as ΔTJ = PD × RθJA. At 350 mA, VIN = 3.6 V, VOUT = 1.875 V, efficiency ≈ 90%, so PD ≈ 0.67 W. With RθJA = 163.3°C/W, ΔTJ ≈ 109°C - exceeding 125°C max rating. Derating to ≤220 mA is required for reliable operation; adding thermal vias or 4-layer board reduces RθJA to ~60°C/W, enabling full 350 mA. LM3670MF-1.875 must be thermally managed per layout guidelines in Section 10.