My Inquiry
My Account
Texas Instruments LM3557SDX-2
- Part No.:
- LM3557SDX-2
- Manufacturer:
- Texas Instruments
- Category:
- LED Drivers
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LM3557SDX-2.pdf
- Description:
- IC LED DRIVER RGLTR 800MA 8WSON
- Quantity:
- Payment:
- Shipping:
Inventory:1,560
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
LM3557SDX-2 from Texas Instruments is a fixed-frequency, current-mode step-up DC/DC converter optimized for white LED backlighting in portable displays. It operates from 2.7V–7.5V input, delivers regulated LED current via feedback-controlled switching at 1.25 MHz, and integrates dual internal MOSFETs (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 applications such as smartphone LCD backlights.
For engineers reviewing the LM3557SDX-2 datasheet, LM3557SDX-2 pinout, LM3557SDX-2 application, or LM3557SDX-2 equivalent, key selection considerations include its 8-pin WSON package with exposed thermal pad, integrated dual-FET topology eliminating external high-side switch, programmable LED current via R2 resistor, and OVP threshold adjustability using an external divider on the Ovp pin.
Technical Context
The LM3557SDX-2 implements constant-frequency current-mode control with a 1.25 MHz oscillator, enabling small external inductors (e.g., 2.2 µH) and ceramic capacitors (Cin = 4.7 µF, Cout = 1 µF). Its dual internal FET architecture-N1 (Sw1) as main power switch and N2 (Sw2) as synchronous rectifier/LED return path-eliminates external diode losses and supports true shutdown by opening the LED string.
Protection features are hardware-based and fully integrated: cycle-by-cycle current limiting (0.8 A typ), input under-voltage lockout (2.2 V turn-on), output over-voltage protection (26 V typ with 500 mV hysteresis), and thermal shutdown at ~150°C. The feedback voltage is referenced to Sw2 (not GND), fixed at 0.51 V, enabling precise LED current regulation independent of output rail voltage.
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 (2.4–3.6 V) inputs without pre-regulation. |
| Switching Frequency | 1.25 MHz (typ) - Enables use of sub-3 mm × 3 mm inductors and low-ESR ceramic capacitors for ultra-compact PCB layout. |
| Feedback Voltage | 0.51 V (typ), referenced to Sw2 pin - Enables accurate LED current setting (ILED = 0.51 V / R2) regardless of output voltage swing. |
| OVP Threshold | 26 V (typ), with 500 mV hysteresis - Protects LEDs and circuitry during open-load or overvoltage fault conditions; adjustable via external resistor divider on Ovp pin. |
| Current Limit | 0.8 A (typ), cycle-by-cycle - Prevents inductor saturation and MOSFET overstress during startup or short-circuit events. |
| Quiescent Current | 2 µA (max) in shutdown - Ensures negligible battery drain when display is off; no DC current paths to ground in TRUE SHUTDOWN mode. |
| Package | 8-pin WSON (NGQ), 2.0 mm × 2.0 mm × 0.8 mm - Exposed DAP improves thermal dissipation; footprint compatible with automated assembly and high-density routing. |
Pinout & Package
LM3557SDX-2 uses an 8-pin, 2.0 mm × 2.0 mm, 0.8 mm profile WSON package (TI drawing NGQ) with exposed die attach pad (DAP) soldered to PCB ground for thermal management.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Sw1 | Main power FET drain | Connects to inductor and diode anode; switches at 1.25 MHz to store energy in inductor during ON time. |
| VIN | Input supply connection | Accepts 2.7–7.5 V; powers internal circuitry and supplies energy to inductor via Sw1 path. |
| NC | No connection | Unbonded pin; must remain unconnected and unstubbed on PCB to avoid parasitic coupling. |
| En | Enable control input | Logic-level input (0.9 V threshold); high enables regulation, low forces TRUE SHUTDOWN with zero ground current. |
| Ovp | OVP sense input | Monitors output voltage via direct connection or resistor divider; triggers shutdown if >26 V (typ). |
| Fb | Feedback input | Senses voltage across current-setting resistor R2; regulates to 0.51 V above Sw2 to set precise LED current. |
| Sw2 | Synchronous rectifier drain | Connects to cathode of LED string and R2; provides low-loss return path and enables true open-circuit shutdown. |
| Gnd | Power and signal ground | Reference for all internal circuits; must be tied to DAP and system ground plane for thermal and noise integrity. |
Key Features
| Feature | Design Value |
|---|---|
| Dual integrated MOSFETs (Sw1 + Sw2) | Eliminates external diode and high-side switch, reducing BOM count, board area, and conduction losses in LED return path. |
| TRUE SHUTDOWN mode | Zero DC current to ground during disable - critical for battery-powered devices requiring ultra-low standby power. |
| No external compensation required | Internally compensated error amplifier enables stable operation with minimal external components and no loop-tuning effort. |
| Input UVLO with hysteresis | Turns on at 2.2 V, turns off at 2.3 V - prevents erratic operation near battery depletion while avoiding oscillation at threshold. |
| Thermal shutdown at ~150°C | Protects device under sustained overload or poor heatsinking; auto-recovery upon cooling ensures robust field operation. |
Applications
| Smartphone LCD Backlight | Portable Media Player Display |
|---|---|
Use Scenario: Driving 4–6 series white LEDs from a single Li-ion cell (3.0–4.2 V) in a 3.5-inch TFT-LCD panel. IC Role / Device Role / Timing Role: Step-up converter providing constant-current LED bias; regulates via Fb/Sw2 feedback loop synchronized to 1.25 MHz clock. Use Value: Achieves >85% efficiency at 20 mA per LED with 2.2 µH inductor and eliminates need for external Schottky diode, reducing solution size by 30% vs discrete boost designs. | Use Scenario: Powering a 2.8-inch OLED display requiring stable 15 mA LED current across varying battery voltage (3.3–4.0 V). IC Role / Device Role / Timing Role: Constant-current boost controller with PWM-dimmable enable input; supports 200–500 Hz dimming without audible noise. Use Value: Enables smooth brightness control down to µA-level currents using EN pin PWM, with no flicker due to fixed 1.25 MHz switching frequency. |
| Handheld Barcode Scanner Illumination | Medical Diagnostic Handheld Display |
Use Scenario: Providing brief, high-intensity illumination pulses (100 ms duration) for CCD-based barcode capture from a 3.6 V NiMH pack. IC Role / Device Role / Timing Role: Fast-response boost regulator with cycle-by-cycle current limit; enables safe pulsed overdrive up to 30 mA without thermal runaway. Use Value: Delivers consistent light output across battery discharge curve; OVP (26 V) protects scanner optics during open-circuit LED failure. | Use Scenario: Driving a ruggedized 4.3-inch sunlight-readable LCD in a battery-operated diagnostic tool requiring -20°C to +70°C operation. IC Role / Device Role / Timing Role: Temperature-stable LED driver with junction temp range -40°C to +125°C; maintains ±5% LED current accuracy over full ambient range. Use Value: Guarantees display luminance consistency in clinical environments; WSON package withstands reflow and mechanical shock per IPC-J-STD-020. |
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 | Single-FET architecture; requires external Schottky diode; 1.2 MHz switching; 28 V OVP; no Sw2 pin. | Lacks synchronous rectification and true shutdown - higher quiescent current (1.5 µA vs 2 µA) and less efficient at low LED currents. | Choose when cost sensitivity outweighs efficiency and board space; verify diode selection for 20–30 mA LED loads. |
| MAX16832ATA+T | Fixed 1.1 MHz frequency; integrated 0.5 Ω high-side switch only; no Sw2; OVP at 29 V; requires external current-sense resistor. | Supports higher output voltages but lacks dual-FET topology - cannot achieve true open-circuit shutdown or Sw2-referenced feedback. | Select for multi-string LED configurations where centralized current sensing is preferred; not suitable for single-string ultra-low-power shutdown. |
Compared with TPS61160DRVR and MAX16832ATA+T, the LM3557SDX-2 uniquely integrates both power and synchronous return FETs, enabling true shutdown, lower component count, and Sw2-referenced feedback for superior current accuracy and efficiency below 10 mA - making it optimal for compact, battery-sensitive portable displays.
Availability
LM3557SDX-2 is available at Aetrix Electronics and suitable for smartphone backlighting, portable media player displays, handheld scanner illumination, and medical diagnostic handheld displays requiring stable component supply and long-term manufacturability.
Supply support for LM3557SDX-2 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 solutions for industrial, automotive, and personal electronics markets.
The LM3557SDX-2 belongs to TI's LED lighting driver portfolio, designed specifically for space-constrained, battery-powered white LED backlight applications demanding high efficiency, low quiescent current, and integrated protection.
FAQ
What is the recommended inductor value for LM3557SDX-2 in a typical smartphone backlight design?
The LM3557SDX-2 datasheet specifies a 2.2 µH inductor (e.g., Coilcraft DO1608C-223) for standard operation. This value balances peak current, ripple, and physical size while maintaining CCM operation across 3.0–4.2 V input and 15–25 mA LED loads. Inductor saturation current must exceed 1.1 A (max cycle-by-cycle limit), and DCR should be minimized to preserve efficiency. Layout requires short, wide traces between Sw1, inductor, and diode.
How does the LM3557SDX-2 achieve true shutdown with zero ground current?
The LM3557SDX-2 achieves true shutdown by turning off both internal FETs: Sw1 (main switch) and Sw2 (synchronous return path). With Sw2 open, the LED string is fully disconnected from ground, eliminating all DC current paths. This results in <2 µA total shutdown current - confirmed in Electrical Characteristics under IQ (VEN = 0 V). No external components are needed to realize this behavior; it is inherent to the dual-FET architecture.
Can the over-voltage protection threshold of LM3557SDX-2 be adjusted, and how?
Yes, the LM3557SDX-2 OVP threshold (26 V typ) can be increased using an external resistor divider on the Ovp pin. Per Figure 12 in the datasheet, connecting R3 and R4 between VOUT and GND, with Ovp tied to the R3/R4 node, scales the sensed voltage. To maintain accuracy, the divider bias current must exceed 100× the Ovp pin leakage (≥100 nA), so R3 + R4 ≤ 270 kΩ is recommended. This allows safe operation up to 35 V output while preserving protection integrity.
What is the function of the Sw2 pin in LM3557SDX-2, and why is it referenced in the feedback equation?
The Sw2 pin is the drain of the internal synchronous rectifier FET and serves as the return path for LED current. The feedback voltage (0.51 V typ) is measured *between Fb and Sw2*, not Fb and GND. This differential sensing rejects common-mode voltage swing on Sw2 during switching, enabling accurate LED current regulation (ILED = 0.51 V / R2) even as the output voltage varies widely - a key advantage for multi-LED strings with dynamic forward voltage.
Does LM3557SDX-2 require external compensation components, and why or why not?
No, the LM3557SDX-2 does not require external compensation components. Its error amplifier and current-mode control loop are fully internally compensated, as stated in the FEATURES list and verified in the APPLICATION INFORMATION section. This eliminates the need for external RC networks, simplifies design, reduces BOM cost, and guarantees stability across all recommended operating conditions - including variations in input voltage, output load, and temperature - without user tuning.
LM3557SDX-2 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 FAQ
1.How can I place an order for LM3557SDX-2 through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3557SDX-2 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 reliable?
The price and inventory of LM3557SDX-2 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 is usually 5 days.
3.What payment methods are accepted for LM3557SDX-2?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3557SDX-2 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3557SDX-2?
LM3557SDX-2 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3557SDX-2 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?
For technical support, including LM3557SDX-2 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3557SDX-2 requirements.
6.How does Aetrix verify that LM3557SDX-2 is sourced from the original manufacturer or authorized distributors?
All LM3557SDX-2 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 meets industry standards.
7.What is the process for return or replacement of LM3557SDX-2?
All LM3557SDX-2 units undergo pre-shipment inspection (PSI). If there is an issue with LM3557SDX-2, 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 part is unused and in its original packaging.
Return procedure for LM3557SDX-2:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LM3557SDX-2 Tags
-
BCR402RE6327HTSA1
Infineon Technologies
-
BCR430UXTSA2
Infineon Technologies
-
BCR420UE6433HTMA1
Infineon Technologies
-
BCR420UE6327HTSA1
Infineon Technologies
-
BCR421UE6327HTSA1
Infineon Technologies
-
LYT1604D-TL
Power Integrations
-
HV9910CLG-G
Microchip Technology
-
CL2N8-G
Microchip Technology
-
BCR420UW6-7
Diodes Incorporated
-
BCR421UW6-7
Diodes Incorporated
-
BCR420UFD-7
Diodes Incorporated
-
BCR421UFD-7
Diodes Incorporated
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
