Key Selection Information
| Selection Parameter | Confirmed Information |
|---|---|
| Topologies | Boost, SEPIC and flyback with external low-side N-MOSFET |
| Input | 2.97 V to 40 V |
| Frequency | 100 kHz to 1 MHz adjustable |
| Gate Drive | 1 A peak internal push-pull driver |
| Control | Current-mode with cycle-by-cycle current limit |
| Reference | ±2.5% over-temperature internal reference stated |
| Features | Soft start, UVLO, thermal shutdown, shutdown power saving |
| Exact Package / Packing | VSSOP (DGK), 8 pins; 3500-piece large reel; −40°C to +125°C; marking S14B |
Product Overview
LM3478MMX/NOPB is a versatile controller for topologies that use one external low-side N-channel MOSFET, especially boost, SEPIC and flyback. It does not contain the main power MOSFET, so the designer chooses switch voltage/current and magnetics for the actual power level.
The 100-kHz-to-1-MHz oscillator range lets the design trade magnetic size against switching loss. Current-mode control simplifies cycle-by-cycle limiting and transient behavior compared with pure voltage-mode approaches.
This 40-V-input generation is simpler than LM3481: it lacks the latter’s 48-V ceiling, synchronization and some adjustable/light-load features. The exact MMX suffix is the 3500-piece VSSOP reel.
For related devices, see HKEQGOO’s DC DC Switching Controllers category.
Technical Specifications
| Parameter | Verified Information |
|---|---|
| Manufacturer | Texas Instruments |
| Exact MPN | LM3478MMX/NOPB |
| Topologies | Boost, SEPIC and flyback with external low-side N-MOSFET |
| Input | 2.97 V to 40 V |
| Frequency | 100 kHz to 1 MHz adjustable |
| Gate Drive | 1 A peak internal push-pull driver |
| Control | Current-mode with cycle-by-cycle current limit |
| Reference | ±2.5% over-temperature internal reference stated |
| Features | Soft start, UVLO, thermal shutdown, shutdown power saving |
| Exact Package / Packing | VSSOP (DGK), 8 pins; 3500-piece large reel; −40°C to +125°C; marking S14B |
| Manufacturer Status | Active / Production |
| Part Marking | S14B |
Functional Highlights
External MOSFET keeps output power scalable
Controller dissipation stays modest while the power transistor and magnetics are selected independently for the target converter.
Topology flexibility supports step-up and isolated/nonisolated variants
The same controller can implement boost, SEPIC or flyback by changing the power stage rather than changing controller family.
Design Considerations
- Select MOSFET voltage margin from topology-specific switch-node stress, not only VIN.
- Choose compensation and current-sense filtering for the exact power stage and switching frequency.
- Verify 40-V input ceiling if the source has automotive/industrial transients.
Product Status and Exact Order Code
Texas Instruments lists LM3478MMX/NOPB as Active / Production; VSSOP (DGK), 8 pins; 3500-piece large tape and reel; −40°C to +125°C; marking S14B.
Related Engineering Resources
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