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Texas Instruments LM3557SD-2/NOPB
- Part No.:
- LM3557SD-2/NOPB
- Manufacturer:
- Texas Instruments
- Category:
- LED Drivers
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LM3557SD-2/NOPB.pdf
- Description:
- IC LED DRIVER RGLTR 800MA 8WSON
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
LM3557SD-2/NOPB from Texas Instruments is a fixed-frequency, current-mode step-up DC/DC converter optimized for driving white LED strings in portable backlighting applications. It operates from 2.7V–7.5V input, delivers regulated LED current via external R2 feedback, integrates dual internal N-channel FETs (Sw1 and Sw2), and features true shutdown with zero DC ground leakage. Its 1.25 MHz switching frequency enables compact 2.2 µH inductors and low-profile ceramic capacitors.
For engineers reviewing the LM3557SD-2/NOPB datasheet, LM3557SD-2/NOPB pinout, LM3557SD-2/NOPB application, or LM3557SD-2/NOPB equivalent, key selection criteria include its integrated dual-FET architecture, OVP/UVP protection thresholds (22–28.5 V / 2.2–2.3 V), thermal shutdown at +150°C, 8-pin WSON package with exposed DAP, and programmable LED current via Fb–Sw2 reference voltage of 0.51 V (±5%).
Technical Context
The LM3557SD-2/NOPB implements constant-frequency current-mode control using an internal error amplifier comparing 0.51 V feedback voltage (Fb relative to Sw2) against a precision reference. Its dual-FET topology-N1 (Sw1) as main power switch and N2 (Sw2) as synchronous rectifier/LED return path-enables high efficiency and true shutdown by opening both paths simultaneously.
Protection logic includes cycle-by-cycle current limiting (0.4–1.1 A), over-voltage protection triggered at 22–28.5 V with 500 mV hysteresis, under-voltage lockout (2.2 V turn-on, 2.3 V turn-off), and thermal shutdown at ~150°C. All protections force N1 gate drive disable without latching, allowing automatic recovery when fault conditions clear.
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), dual-cell alkaline (2.4–3.2 V), or USB-powered systems without pre-regulation. |
| Switching Frequency | 1.25 MHz (typ.) - enables use of sub-3 mm × 3 mm inductors and reduces output ripple without increasing EMI filtering complexity. |
| Fb Reference Voltage | 0.51 V ±5% (vs Sw2) - sets LED current via R2 = VFb-Sw2 / ILED; enables precise, temperature-stable current programming. |
| OVP Threshold | 22 V to 28.5 V - protects LEDs and output capacitor during open-circuit or overvoltage fault; hysteresis prevents chatter near threshold. |
| UVP Threshold | 2.2 V (turn-on), 2.3 V (turn-off) - prevents operation below minimum battery voltage, avoiding unstable regulation and excessive quiescent current. |
| Quiescent Current | 0.01 µA (shutdown), 0.55 mA (active) - minimizes battery drain in standby while maintaining fast wake-up response. |
| RDS(ON) (Sw1) | 800–1000 mΩ - limits conduction loss at peak switch current; combined with 1.1 A current limit, defines maximum deliverable LED power. |
Pinout & Package
LM3557SD-2/NOPB uses an 8-pin, 2.0 mm × 2.0 mm, 0.75 mm profile WSON package (NGQ drawing) with exposed die attach pad (DAP) soldered to PCB ground for thermal management.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Sw1 (Pin 1) | Drain of main power FET (N1) | Connects to inductor and diode anode; carries full switching current; requires low-inductance layout 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 | Unbonded pad; may be left floating or tied to GND for mechanical stability-no electrical function. |
| En (Pin 4) | Enable control input | Active-high logic interface; 0.9 V threshold ensures compatibility with 1.8 V/3.3 V GPIO; supports PWM dimming up to 1 kHz. |
| Ovp (Pin 5) | Over-voltage protection sense | Monitors output voltage; internal comparator triggers shutdown if >22–28.5 V; bias current ≤10 µA allows resistor-divider scaling. |
| Fb (Pin 6) | Feedback voltage input | Senses voltage across R2 (between Sw2 and Fb); regulates LED current by holding Fb–Sw2 = 0.51 V ±5%. |
| Sw2 (Pin 7) | Drain of synchronous FET (N2) | Completes LED current path to ground; turns off during shutdown to eliminate DC leakage; RDS(on) = 8–10 Ω affects low-current efficiency. |
| Gnd (Pin 8) | Power and signal ground reference | Primary return path; DAP must be soldered to solid ground plane to achieve θJA = 55°C/W and prevent thermal shutdown. |
Key Features
| Feature | Design Value |
|---|---|
| True shutdown mode | Zero DC current to ground via simultaneous disable of Sw1 and Sw2 - eliminates battery drain in display-off state. |
| No external compensation required | Internally compensated error amplifier - simplifies design, removes risk of instability from incorrect RC network selection. |
| Integrated dual N-channel FETs | Sw1 (main boost switch) + Sw2 (synchronous return path) - eliminates need for external Schottky diode and reduces conduction losses. |
| Fixed 1.25 MHz switching | Enables use of miniature 2.2 µH inductors and 1 µF ceramic output capacitors - reduces board area and BOM count. |
| Output over-voltage protection | Programmable 22–28.5 V threshold with 500 mV hysteresis - safeguards LEDs and output capacitor during open-load faults. |
| Cycle-by-cycle current limit | 0.4–1.1 A peak switch current limit - prevents inductor saturation and device damage during startup or short-circuit events. |
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 a slim smartphone form factor. IC Role / Device Role / Timing Role: Step-up converter providing constant-current LED drive with PWM dimming support via En pin. Use Value: Delivers >85% efficiency at 20 mA per LED while maintaining <1 mm profile via 2.0 mm × 2.0 mm WSON package and 2.2 µH inductor. |
Use Scenario: Powering QVGA or VGA LCD backlight in handheld PDA with variable brightness and battery life optimization. IC Role / Device Role / Timing Role: Constant-current LED driver with UVP/OVP protection and true shutdown to extend standby time. Use Value: Enables 0.01 µA shutdown current and 0.55 mA operating IQ - extends battery runtime by >30% versus discrete boost solutions. |
| Portable Media Player Display | Ultra-Thin Tablet Backlight |
|
Use Scenario: Driving parallel LED strings in a 3.5-inch OLED/LCD screen powered by dual AA batteries (2.4–3.2 V). IC Role / Device Role / Timing Role: Wide-input boost regulator with integrated FETs and programmable current setting via R2. Use Value: Supports 2.7 V minimum VIN and delivers stable current down to 1 mA - maintains uniform brightness across full battery discharge curve. |
Use Scenario: High-efficiency backlight solution for 7-inch tablet with thermal constraints and strict height budget (<1 mm). IC Role / Device Role / Timing Role: Compact, thermally optimized LED driver with DAP-connected ground plane for junction-to-ambient θJA = 55°C/W. Use Value: Maintains full output capability at +85°C ambient without derating - eliminates need for thermal pads or heatsinks in thin-profile designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar white LED boost driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS61160DRVR | Single-FET architecture; requires external Schottky diode; 1.2 MHz switching; 0.5 V feedback reference. | Lacks true shutdown (leakage path through diode); lower integration increases board area and component count. | Choose when cost sensitivity outweighs size/efficiency; verify diode selection meets IFRM ≥ ILpeak and VR > VOUT. |
| MAX16832ATA+T | Current-mode boost controller (external MOSFETs); 2.2 MHz switching; adjustable OVP/UVP; no integrated FETs. | Requires external high-side and low-side switches; greater design flexibility but longer development cycle and layout sensitivity. | Prefer for high-power (>100 mA) or multi-string configurations where thermal management justifies discrete FET selection. |
Compared with TPS61160DRVR and MAX16832ATA+T, LM3557SD-2/NOPB offers superior integration (dual internal FETs), lowest profile (0.75 mm), and true shutdown - reducing bill-of-materials, PCB area, and standby power in space-constrained portable displays.
Availability
LM3557SD-2/NOPB is available at Aetrix Electronics and suitable for cellular phone backlighting, PDA display lighting, and portable media player applications requiring stable component supply and long-term design continuity.
Supply support for LM3557SD-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 delivering analog, embedded processing, and connectivity technologies for industrial, automotive, and personal electronics markets.
LM3557SD-2/NOPB belongs to TI's LED lighting driver portfolio, engineered specifically for ultra-compact, high-efficiency white LED backlighting in battery-powered portable devices with stringent height and power constraints.
FAQ
What is the recommended inductor value for LM3557SD-2/NOPB in a typical 4-LED string application?
The LM3557SD-2/NOPB datasheet specifies 2.2 µH as the standard inductor value for most white LED backlight configurations. This value balances efficiency, ripple current, and physical size-especially critical in thin portable devices. For 3.6 V input and 12 V output at 20 mA, 2.2 µH yields ~300 mA peak inductor current and maintains continuous conduction mode. Coilcraft DO1608C-223 is a validated option meeting saturation and DCR requirements.
How does LM3557SD-2/NOPB implement true shutdown, and why is it important for battery life?
LM3557SD-2/NOPB achieves true shutdown by simultaneously disabling both internal N-channel FETs (Sw1 and Sw2), eliminating all DC current paths to ground. Unlike controllers requiring external diodes-which leak reverse current-this architecture guarantees <2 µA total shutdown current. In a smartphone with daily display-off periods exceeding 18 hours, this reduces annual battery drain by over 40% compared to non-true-shutdown alternatives.
Can LM3557SD-2/NOPB drive more than six white LEDs in series?
LM3557SD-2/NOPB supports output voltages up to 35 V, enabling up to eight 3.2 V white LEDs in series (25.6 V typical forward drop). However, the OVP threshold is fixed at 22–28.5 V, so driving >6 LEDs requires external resistor-divider scaling on the Ovp pin to avoid premature shutdown. The internal 1.1 A current limit and thermal design also constrain maximum string current at higher VOUT.
What is the purpose of the NC pin (Pin 3) on LM3557SD-2/NOPB, and how should it be handled on the PCB?
Pin 3 (NC) on LM3557SD-2/NOPB is an unconnected die pad with no internal bond wire or circuitry. It serves only mechanical stabilization and thermal relief. TI recommends leaving it floating or connecting it to GND via a small copper pour-not for electrical function, but to improve solder joint reliability and heat spreading. Never route signals or power through this pin.
How does the Fb–Sw2 reference voltage of 0.51 V affect LED current accuracy and temperature stability?
The LM3557SD-2/NOPB regulates LED current by maintaining 0.51 V ±5% between Fb and Sw2 pins. This reference exhibits <100 ppm/°C drift over −40°C to +125°C, ensuring LED current variation remains within ±6% across temperature. Combined with low-tolerance external R2 (e.g., 1% metal-film), system-level current accuracy stays within ±8%-critical for consistent display luminance in consumer devices.
LM3557SD-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)
LM3557SD-2/NOPB FAQ
1.How can I place an order for LM3557SD-2/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3557SD-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 LM3557SD-2/NOPB reliable?
The price and inventory of LM3557SD-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 LM3557SD-2/NOPB is usually 5 days.
3.What payment methods are accepted for LM3557SD-2/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3557SD-2/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3557SD-2/NOPB?
LM3557SD-2/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3557SD-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 LM3557SD-2/NOPB?
For technical support, including LM3557SD-2/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3557SD-2/NOPB requirements.
6.How does Aetrix verify that LM3557SD-2/NOPB is sourced from the original manufacturer or authorized distributors?
All LM3557SD-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 LM3557SD-2/NOPB meets industry standards.
7.What is the process for return or replacement of LM3557SD-2/NOPB?
All LM3557SD-2/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM3557SD-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 LM3557SD-2/NOPB part is unused and in its original packaging.
Return procedure for LM3557SD-2/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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