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Texas Instruments LM3557SDX-2/NOPB
- Part No.:
- LM3557SDX-2/NOPB
- Manufacturer:
- Texas Instruments
- Category:
- LED Drivers
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LM3557SDX-2/NOPB.pdf
- Description:
- IC LED DRIVER RGLTR 800MA 8WSON
- Quantity:
- Payment:
- Shipping:
Inventory:2,490
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Product details
Overview
LM3557SDX-2/NOPB from Texas Instruments is a fixed-frequency, current-mode step-up DC/DC converter optimized for white LED backlighting in portable devices. It operates from 2.7V–7.5V input, delivers regulated LED current via feedback-controlled switching at 1.25 MHz, and integrates dual internal N-channel FETs (Sw1 and Sw2) with cycle-by-cycle current limit, output over-voltage protection (26 V typ), and true shutdown with zero DC ground leakage. It targets space-constrained mobile displays requiring high efficiency and minimal external components.
For engineers reviewing the LM3557SDX-2/NOPB datasheet, LM3557SDX-2/NOPB pinout, LM3557SDX-2/NOPB application, or LM3557SDX-2/NOPB equivalent, key selection criteria include its 8-pin WSON package with thermal DAP, 0.51 V feedback reference referenced to Sw2, 0.8 A typical power switch current limit, and integrated UVP/OVP protection thresholds - all critical for LED current accuracy, thermal reliability, and system-level fault resilience in battery-powered lighting designs.
Technical Context
The LM3557SDX-2/NOPB implements constant-frequency current-mode control using an internal error amplifier comparing 0.51 V (Fb–Sw2) against a precision reference. Its dual-FET architecture separates energy storage (Sw1-driven inductor) from LED return path (Sw2-switched ground), enabling precise current regulation without sensing resistor voltage drop across ground. The 1.25 MHz oscillator enables use of sub-2.2 µH inductors and low-ESR ceramic capacitors.
Protection logic includes cycle-by-cycle peak current limiting on Sw1 (0.8 A typ), hysteresis-based OVP (26 V on-threshold, 25.5 V off-threshold), and UVP (2.2 V off-threshold, 2.3 V on-threshold). Thermal shutdown activates at ~150°C junction temperature, and TRUE SHUTDOWN disables both FETs with <2 µA quiescent current while opening the LED string.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.7 V to 7.5 V - supports single-cell Li-ion (3.0–4.2 V) and dual-cell alkaline/NiMH (2.4–3.2 V) inputs without pre-regulation. |
| Switching Frequency | 1.25 MHz (typ) - enables compact 2.2 µH inductors and 4.7 µF input/1 µF output ceramic capacitors; reduces EMI fundamental frequency. |
| Fb Reference Voltage | 0.51 V (typ), referenced to Sw2 pin - sets LED current via external R2: ILED = 0.51 V / R2; eliminates ground-referenced sense resistor errors. |
| Power Switch Current Limit | 0.8 A (typ) - limits peak inductor current to prevent saturation and thermal overstress under shorted-LED or high-VOUT conditions. |
| OVP Threshold | 26 V (typ), with 500 mV hysteresis - protects LEDs and output capacitor from overvoltage during open-circuit or dimming transients. |
| Quiescent Current (Shutdown) | 0.01 µA (min) - ensures negligible battery drain when display is off; no DC path from VIN or LED string to GND. |
| Junction Temp Range | −40°C to +125°C - validated for operation in handheld enclosures with limited airflow and ambient temperatures up to 85°C. |
Pinout & Package
LM3557SDX-2/NOPB uses an 8-pin, 2.0 mm × 2.0 mm, 0.75 mm max height WSON package (NGQ drawing) with exposed die attach pad (DAP) soldered to PCB ground for thermal dissipation. Pin 1 is Sw1 (N1 drain); pin 8 is Gnd; DAP must be connected to solid ground plane per TI layout guidelines.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Sw1 (Pin 1) | Drain of internal high-side N-FET (N1) | Connects to inductor input; carries full switching current; requires low-inductance routing to minimize voltage spikes. |
| VIN (Pin 2) | Main input supply connection | Accepts 2.7–7.5 V; must be decoupled with ≤2.0 µF low-ESR ceramic capacitor placed adjacent to pin. |
| NC (Pin 3) | No internal connection | Must remain unconnected; no trace or pad required beyond mechanical clearance. |
| En (Pin 4) | Enable control input | Active-high: ≥0.9 V turns device on; ≤0.3 V forces shutdown; supports PWM dimming at 100–1 kHz. |
| Ovp (Pin 5) | Over-voltage protection monitor | Monitors output voltage; triggers shutdown if >26 V; optional resistor divider allows threshold adjustment. |
| Fb (Pin 6) | Feedback voltage input | Senses voltage across R2; regulates to 0.51 V above Sw2; sets LED current without ground-referenced loss. |
| Sw2 (Pin 7) | Drain of internal low-side N-FET (N2) | Switches LED cathode to ground; enables true shutdown by opening LED string; connects to R2 bottom terminal. |
| Gnd (Pin 8) | Power and signal ground reference | Primary ground return; DAP must be soldered to same ground plane for thermal and noise performance. |
Key Features
| Feature | Design Value |
|---|---|
| TRUE SHUTDOWN mode | Zero DC current paths to ground during disable - eliminates standby battery drain and prevents unintended LED glow. |
| Dual integrated N-FETs (Sw1/Sw2) | Eliminates need for external high-voltage diode and current-sense resistor - reduces BOM count and board area by ≥3 components. |
| 1.25 MHz fixed switching frequency | Enables use of 2.2 µH inductors and 1 µF ceramic output capacitors - cuts solution size vs. 500 kHz alternatives by >40%. |
| Output over-voltage protection (OVP) | 26 V threshold with 500 mV hysteresis - prevents LED and capacitor damage during open-circuit faults or PWM dimming overshoot. |
| No external compensation required | Internally compensated error amplifier - simplifies design validation and eliminates stability tuning iterations. |
Applications
| Cellular Phone Backlight | PDA Display Lighting |
|---|---|
Use Scenario: Driving 4–6 white LEDs in series from a 3.6 V Li-ion battery in slim handset form factor. IC Role / Device Role / Timing Role: Step-up converter regulating constant LED current via Fb–Sw2 feedback; Sw2 provides true open-circuit shutdown. Use Value: Achieves >85% efficiency at 20 mA per LED while maintaining ±3% current accuracy across battery discharge (3.0–4.2 V) and temperature (−20°C to +70°C). | Use Scenario: Powering QVGA TFT LCD backlight with variable brightness in handheld PDA with limited PCB real estate. IC Role / Device Role / Timing Role: High-frequency boost controller enabling compact 2.0 mm × 2.0 mm layout; En pin accepts 200–500 Hz PWM for smooth dimming. Use Value: Reduces total solution footprint by 35% vs. discrete boost + linear regulator approach, with no external compensation or sense resistor. |
| Portable Media Player UI Light | Handheld Barcode Scanner Indicator |
Use Scenario: Illuminating OLED status icons and navigation keys in battery-operated media players. IC Role / Device Role / Timing Role: Low-quiescent-current boost IC delivering 5–15 mA LED current; UVP prevents operation below 2.2 V to preserve battery health. Use Value: Extends usable battery life by 12% versus competing solutions due to 0.01 µA shutdown current and 1.25 MHz efficiency optimization. | Use Scenario: Driving high-brightness indicator LED in industrial barcode scanners subject to vibration and wide ambient temperature swings. IC Role / Device Role / Timing Role: Robust LED driver with thermal shutdown (150°C) and cycle-by-cycle current limit - sustains operation under intermittent load faults. Use Value: Eliminates field failures from LED open-circuit events via OVP-triggered shutdown and maintains current accuracy within ±4% from −40°C to +85°C. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar white LED boost converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS61160DRVR | Higher 1.2-MHz switching frequency; 28-V OVP; requires external compensation; no Sw2 FET - needs external MOSFET for true shutdown. | Lacks integrated low-side switch; requires additional component for open-circuit LED protection and zero-ground-current shutdown. | Select when higher OVP threshold or adjustable frequency is needed; accept added BOM and layout complexity. |
| MAX16832ATA+T | Fixed 600-kHz frequency; 36-V OVP; integrated high-side FET only; uses ground-referenced current sense. | Lower switching frequency increases inductor size; ground-referenced sensing introduces offset errors and reduces current accuracy at low ILED. | Prefer for cost-sensitive designs where 2.2 µH inductor size is acceptable and ±5% LED current tolerance is sufficient. |
Compared with TPS61160DRVR and MAX16832ATA+T, LM3557SDX-2/NOPB uniquely integrates both high- and low-side FETs in a thermally enhanced WSON package, enabling true shutdown, superior current accuracy via Sw2-referenced feedback, and smallest total solution size - making it optimal for ultra-thin portable displays demanding minimal external components and zero standby leakage.
Availability
LM3557SDX-2/NOPB is available at Aetrix Electronics and suitable for cellular phone backlighting, PDA display lighting, and portable media player UI illumination requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for LM3557SDX-2/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 digital signal processing technologies, with decades of expertise in power management ICs for portable electronics.
The LM3557 product line was designed specifically for space-constrained white LED backlighting in battery-powered handheld devices, emphasizing integration, thermal efficiency, and simplified bill-of-materials through dual-FET architecture and no-external-compensation operation.
FAQ
What is the recommended inductor value for LM3557SDX-2/NOPB in a typical 4-LED backlight application?
TI recommends a 2.2 µH shielded power inductor (e.g., Coilcraft DO1608C-223) for LM3557SDX-2/NOPB in standard white LED backlight configurations. This value balances peak current handling (≤0.8 A), size constraints (≤2.0 mm × 2.0 mm footprint), and efficiency (>85% at 20 mA per LED). Inductor saturation current must exceed calculated peak inductor current - typically 1.2× ILED/(1−D), where D ≈ VOUT/(VOUT−VIN) - and DCR should be <150 mΩ to minimize conduction losses. LM3557SDX-2/NOPB's 1.25 MHz operation makes this inductance optimal for minimizing solution size without compromising stability.
How does the LM3557SDX-2/NOPB achieve true shutdown with no DC current paths to ground?
The LM3557SDX-2/NOPB achieves true shutdown by simultaneously disabling both internal N-channel FETs: Sw1 (high-side) and Sw2 (low-side). When the En pin falls below 0.3 V, the control logic turns off Sw1 to halt energy transfer and opens Sw2 to disconnect the LED cathode from ground - leaving the entire LED string floating. This eliminates all DC current paths from VIN, the LED anodes, or the output node to GND, resulting in <2 µA total shutdown current. This behavior is confirmed in the datasheet's "TRUE SHUTDOWN" section and distinguishes LM3557SDX-2/NOPB from boost converters requiring external MOSFETs or diodes to achieve comparable leakage performance.
Can the LM3557SDX-2/NOPB drive more than six white LEDs in series?
No - LM3557SDX-2/NOPB is not rated to drive more than six white LEDs in series. Its 26 V typical over-voltage protection threshold and 40 V absolute maximum Sw1 voltage rating limit practical output voltage to ≤30 V. Assuming 3.2 V forward voltage per LED at 20 mA, six LEDs require ~19.2 V, leaving ~6.8 V margin for diode drop, trace loss, and ripple. Driving seven LEDs (≥22.4 V) risks triggering OVP during transient conditions or reducing design margin for temperature drift and manufacturing variance. For higher LED counts, TI recommends alternatives like TPS61165 or discrete boost + linear solutions.
What is the purpose of the Sw2 pin on the LM3557SDX-2/NOPB, and how does it differ from conventional boost controllers?
The Sw2 pin on LM3557SDX-2/NOPB is the drain terminal of an integrated low-side N-channel FET that switches the LED cathode to ground. Unlike conventional boost controllers that rely on a diode or external MOSFET for the return path, Sw2 enables direct current sensing referenced to the switching node (not ground), eliminating sense resistor power loss and offset errors. It also enables true shutdown by opening the LED string, and allows programmable LED current via R2 placed between Fb and Sw2 - where feedback voltage is measured relative to Sw2, not GND. This architecture improves accuracy, efficiency, and safety beyond standard diode-based or high-side-sense boost ICs.
Does the LM3557SDX-2/NOPB require external compensation components?
No, the LM3557SDX-2/NOPB does not require external compensation components. Its error amplifier and current-mode control loop are fully internally compensated, as stated in the datasheet's "FEATURES" list and verified in the "APPLICATION INFORMATION" section. This eliminates the need for external RC networks, simplifies PCB layout, and removes stability tuning steps during design-in. The fixed 1.25 MHz switching frequency and integrated compensation ensure robust performance across input voltage (2.7–7.5 V), output load (5–30 mA), and temperature (−40°C to +125°C) without user-adjustable parameters - a key differentiator versus controllers like TPS61088 that mandate external compensation for stability.
LM3557SDX-2/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 8-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- DC DC Regulator
- Topology:
- Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 2.7V
- Voltage - Supply (Max):
- 7.5V
- Voltage - Output:
- -
- Current - Output / Channel:
- 800mA (Switch)
- Frequency:
- 1.2MHz
- Dimming:
- -
- Applications:
- Backlight
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-WSON (3x3)
LM3557SDX-2/NOPB FAQ
1.How can I place an order for LM3557SDX-2/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3557SDX-2/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 LM3557SDX-2/NOPB reliable?
The price and inventory of LM3557SDX-2/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM3557SDX-2/NOPB is usually 5 days.
3.What payment methods are accepted for LM3557SDX-2/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3557SDX-2/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3557SDX-2/NOPB?
LM3557SDX-2/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3557SDX-2/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 LM3557SDX-2/NOPB?
For technical support, including LM3557SDX-2/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3557SDX-2/NOPB requirements.
6.How does Aetrix verify that LM3557SDX-2/NOPB is sourced from the original manufacturer or authorized distributors?
All LM3557SDX-2/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 LM3557SDX-2/NOPB meets industry standards.
7.What is the process for return or replacement of LM3557SDX-2/NOPB?
All LM3557SDX-2/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM3557SDX-2/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 LM3557SDX-2/NOPB part is unused and in its original packaging.
Return procedure for LM3557SDX-2/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LM3557SDX-2/NOPB Tags
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