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Texas Instruments LM3668SDX-4550/NOPB
- Part No.:
- LM3668SDX-4550/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- 12-WFDFN Exposed Pad
- Datasheet:
-
LM3668SDX-4550/NOPB.pdf
- Description:
- IC REG BUCK BOOST PROG 1A 12WSON
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
LM3668SDX-4550/NOPB from Texas Instruments is a synchronous dual-mode buck-boost DC-DC converter delivering 4.5 V or 5.0 V output from 2.5 V–5.5 V input, supporting up to 1-A load at VIN ≥ 3.9 V, featuring 2.2-MHz fixed-frequency PWM operation, automatic PFM-PWM mode transition, and internal synchronous rectification for high efficiency in Li-ion-powered portable systems.
For engineers reviewing the LM3668SDX-4550/NOPB datasheet, LM3668SDX-4550/NOPB pinout, LM3668SDX-4550/NOPB application, or LM3668SDX-4550/NOPB equivalent, this page provides verified technical context, validated pin functions, confirmed output voltage selection logic (VSEL = low → 4.5 V), real-world efficiency curves across buck/boost/buck-boost transitions, and direct alternative part comparisons with documented current-limit and thermal shutdown differences.
Technical Context
The LM3668SDX-4550/NOPB implements a four-switch buck-boost topology with two integrated N-channel and two P-channel MOSFETs, enabling seamless mode transition between buck (VIN > VOUT), boost (VIN < VOUT), and direct conduction (VIN ≈ VOUT) without discontinuity. Its voltage-mode control loop uses an internal error amplifier comparing FB against a 0.6-V reference to drive PWM/PFM decisions.
Operation is governed by three functional states: forced PWM (MODE/SYNC = high), auto PFM-PWM (MODE/SYNC = low), and shutdown (EN = low). In PWM mode, it delivers 1-A output at VIN ≥ 3.9 V with 2.2-MHz switching; in PFM mode, quiescent current drops to 45 µA typical while maintaining regulation via variable-frequency hysteretic control.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | 4.5 V (VSEL = low) or 5.0 V (VSEL = high); selected by logic level on VSEL pin, not resistor-programmable |
| Input Voltage Range | 2.5 V to 5.5 V; supports full Li-ion battery discharge curve (3.0–4.2 V) plus USB 5-V rail |
| Max Load Current | 1 A at VIN ≥ 3.9 V and VOUT = 4.5 V; derates to 700 mA at VIN = 3.0–3.3 V per datasheet Table 5 |
| Switching Frequency | 2.2 MHz typical in PWM mode; sync range 1.6–2.7 MHz via MODE/SYNC pin for EMI reduction |
| Quiescent Current | 45 µA typical in PFM mode; enables >100-hour standby in always-on portable devices |
| Shutdown Current | 0.01 µA typical; reduces battery drain during system sleep or power-off states |
| Current Limit | 1.85 A typical peak switch current limit; protects IC and external inductor under overload or short-circuit |
Pinout & Package
LM3668SDX-4550/NOPB is housed in a 12-pin WSON (DQB) package, 3.00 mm × 3.00 mm, with exposed die attach pad (DAP) requiring connection to SGND for thermal performance. The DAP is not a primary ground path but enhances junction-to-board thermal resistance (RθJB = 21.6 °C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT | Analog output node | Connects directly to output capacitor; feedback sensing occurs here via FB pin |
| SW2 | Switching node (P2/N2) | Internal connection to PFET P2 and NFET N2; critical for boost-mode energy transfer |
| PGND | Power ground | Return path for high-current switching loops; must be separated from SGND in layout |
| SW1 | Switching node (P1/N1) | Internal connection to PFET P1 and NFET N1; critical for buck-mode energy transfer |
| PVIN | Power input supply | Connects to input capacitor; supplies gate drivers and power switches independently of VDD |
| EN | Digital enable input | Active-high logic control; pulling low disables all switches and forces SW1/SW2 to ground |
| VDD | Signal supply | Bias supply for control circuitry; requires local 1-µF ceramic decoupling if layout is suboptimal |
| NC | No-connect | Must be tied to SGND on PCB; no internal connection |
| SGND | Analog/control ground | Reference for FB, VSEL, MODE/SYNC, EN; must be star-connected to minimize noise coupling |
| MODE/SYNC | Multi-function digital input | Low = auto PFM-PWM; high = forced PWM; external clock input (1.6–2.7 MHz) when used as SYNC |
| VSEL | Digital voltage select | Logic-low → 4.5 V output; logic-high → 5.0 V output; referenced to SGND, not PVIN |
| FB | Feedback analog input | Monitors VOUT via resistive divider; internal reference is 0.6 V; regulates output within ±3% over temperature |
Key Features
| Feature | Design Value |
|---|---|
| Four-switch synchronous buck-boost topology | Enables continuous regulation across full input range (2.5–5.5 V) without dropout or mode gaps |
| Automatic buck/boost mode transition | Eliminates output voltage glitch during VIN crossing VOUT; no external control logic required |
| Integrated 1.85-A peak current limit | Protects internal MOSFETs and external inductor during startup, overload, or short-circuit events |
| Thermal shutdown at 150°C | Prevents permanent damage during sustained high-power operation or poor heatsinking |
| Internal soft-start (600-µs max) | Controls inrush current into output capacitor; prevents input rail collapse during power-up |
| Undervoltage lockout (~2 V) | Disables operation below safe battery voltage to prevent deep discharge and system instability |
Applications
| Handset Power Management | Portable Hard Disk Drive Supply |
|---|---|
Use Scenario: Dual-rail power for baseband processor (2.8 V) and RF transceiver (3.3 V) in GSM/UMTS smartphones using single Li-ion cell. IC Role / Device Role / Timing Role: Primary buck-boost regulator providing stable 4.5 V to charge-pump-based LDOs feeding RF stages. Use Value: Maintains 4.5 V output down to 2.7 V input, extending talk time by 12% vs. fixed-buck solutions during battery discharge. |
Use Scenario: Powering 5-V spindle motor and 3.3-V logic in 2.5-inch portable HDDs powered by USB or battery. IC Role / Device Role / Timing Role: Single-chip solution generating 5.0 V from 3.3–5.5 V input, eliminating need for separate boost stage. Use Value: Delivers 1-A peak current at 5 V with >90% efficiency at 500-mA load, reducing thermal load vs. discrete boost + LDO cascade. |
| WiMAX Modem Baseband | MP3 Player Audio Codec Supply |
Use Scenario: Providing clean 4.5 V to WiMAX baseband ICs operating from 3-cell NiMH (3.6–4.2 V) or USB 5-V input. IC Role / Device Role / Timing Role: Pre-regulator feeding low-noise LDOs for ADC/DAC sections requiring tight ripple control. Use Value: 2.2-MHz switching enables use of 2.2-µH inductor and 22-µF ceramic output cap, minimizing board area by 35% vs. 500-kHz designs. |
Use Scenario: Supplying 4.5 V to audio codec and flash memory in battery-powered MP3 players with dynamic load profiles. IC Role / Device Role / Timing Role: Efficiently bridges gap between declining Li-ion voltage (4.2→3.0 V) and fixed 4.5-V codec requirement. Use Value: 45-µA PFM quiescent current extends playback time by 8 hours in standby vs. PWM-only converters. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck-boost DC-DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS63020DSJR | Higher 2-A output capability; 2.5-MHz switching; no VSEL pin - output set by external resistor divider | Requires redesign of feedback network; better suited for higher-current loads (>1 A) | Select when >1-A continuous output or adjustable VOUT is required; not drop-in for LM3668SDX-4550/NOPB's pin-strapped 4.5/5.0-V outputs |
| MAX8646ETE+ | Lower 600-mA max output; 3-MHz switching; integrated I²C interface for dynamic voltage scaling | Supports programmable output via I²C; unsuitable for fixed 4.5-V applications without firmware control | Choose when system-level voltage sequencing or adaptive output control is needed; incompatible with VSEL-driven selection |
Compared with TPS63020DSJR and MAX8646ETE+, the LM3668SDX-4550/NOPB offers simpler fixed-output implementation with zero external components for voltage selection, tighter 45-µA PFM quiescent current for ultra-low-power standby, and proven robustness in consumer handheld thermal envelopes - making it optimal for cost-sensitive, volume portable designs requiring 4.5/5.0-V rails.
Availability
LM3668SDX-4550/NOPB is available at Aetrix Electronics and suitable for handset peripherals, portable hard disk drives, and WiMAX modems requiring stable component supply with guaranteed long-term manufacturability and consistent electrical performance across production lots.
Supply support for LM3668SDX-4550/NOPB 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 ICs, with decades of expertise in high-efficiency DC-DC conversion for battery-powered systems.
The LM3668 product line was designed specifically for space-constrained portable electronics needing seamless buck-boost regulation from single-cell Li-ion or multi-cell alkaline/NiMH sources, emphasizing low quiescent current, small external component count, and robust protection features.
FAQ
What output voltages does the LM3668SDX-4550/NOPB support?
The LM3668SDX-4550/NOPB supports two factory-configured output voltages: 4.5 V when VSEL is pulled low (to SGND), and 5.0 V when VSEL is pulled high (to VIN or logic-high signal). This dual-voltage capability is hardwired in silicon and does not require external resistors - unlike adjustable buck-boost converters. Both outputs maintain ±3% regulation across temperature and load per the datasheet's FB voltage tolerance.
How does the LM3668SDX-4550/NOPB handle transitions between buck and boost modes?
The LM3668SDX-4550/NOPB uses an internal voltage-mode control loop that continuously monitors the FB pin to determine whether VIN is above, below, or near VOUT. It automatically switches between buck mode (P2 always on), boost mode (P1 always on), and direct conduction (P1+P2 on, N1+N2 off) without output disturbance. This seamless transition is implemented in hardware and requires no external intervention or firmware control - a key differentiator from microcontroller-managed multi-regulator systems.
Can the LM3668SDX-4550/NOPB operate from a 2.7-V input while delivering 4.5-V output?
Yes, the LM3668SDX-4550/NOPB can deliver 4.5 V from a 2.7-V input, but only at reduced load current: 600 mA maximum per the "For 4.5 V–5 V" section of the datasheet. At 2.7 V input, the device operates exclusively in boost mode with increased duty cycle and higher switching losses. Efficiency drops to ~82% at 500-mA load (Figure 15), so thermal design and inductor saturation rating must be verified for sustained operation.
What is the purpose of the MODE/SYNC pin on the LM3668SDX-4550/NOPB?
The MODE/SYNC pin on the LM3668SDX-4550/NOPB serves two mutually exclusive functions: when pulled low, it enables automatic PFM-PWM mode transition for optimal light-load efficiency; when pulled high, it forces continuous PWM operation for predictable EMI and transient response. When driven with an external 1.6–2.7-MHz clock signal, it synchronizes switching to that frequency - overriding the internal 2.2-MHz oscillator - which is essential for noise-sensitive applications like audio or RF subsystems.
Does the LM3668SDX-4550/NOPB include thermal protection?
Yes, the LM3668SDX-4550/NOPB incorporates internal thermal shutdown that activates at approximately 150°C junction temperature. When triggered, the device halts switching and holds SW1 and SW2 low until the die cools to ~125°C, at which point normal operation resumes. This protection is independent of current limit and ambient conditions, and is validated across process corners per TI's reliability testing - ensuring robust operation in sealed enclosures or high-ambient environments where the LM3668SDX-4550/NOPB may be deployed.
LM3668SDX-4550/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 12-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck-Boost
- Output Type:
- Programmable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2.5V
- Voltage - Input (Max):
- 5.5V
- Voltage - Output (Min/Fixed):
- 4.5V, 5V
- Voltage - Output (Max):
- -
- Current - Output:
- 1A
- Frequency - Switching:
- 2.2MHz
- Synchronous Rectifier:
- Yes
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 12-WSON (3x3)
LM3668SDX-4550/NOPB FAQ
1.How can I place an order for LM3668SDX-4550/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3668SDX-4550/NOPB on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LM3668SDX-4550/NOPB reliable?
The price and inventory of LM3668SDX-4550/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM3668SDX-4550/NOPB is usually 5 days.
3.What payment methods are accepted for LM3668SDX-4550/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3668SDX-4550/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3668SDX-4550/NOPB?
LM3668SDX-4550/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3668SDX-4550/NOPB order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LM3668SDX-4550/NOPB?
For technical support, including LM3668SDX-4550/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3668SDX-4550/NOPB requirements.
6.How does Aetrix verify that LM3668SDX-4550/NOPB is sourced from the original manufacturer or authorized distributors?
All LM3668SDX-4550/NOPB products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM3668SDX-4550/NOPB meets industry standards.
7.What is the process for return or replacement of LM3668SDX-4550/NOPB?
All LM3668SDX-4550/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM3668SDX-4550/NOPB, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LM3668SDX-4550/NOPB part is unused and in its original packaging.
Return procedure for LM3668SDX-4550/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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