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Texas Instruments LM3551SDX
- Part No.:
- LM3551SDX
- Manufacturer:
- Texas Instruments
- Category:
- LED Drivers
- Package:
- 14-WFDFN Exposed Pad
- Datasheet:
-
LM3551SDX.pdf
- Description:
- IC LED DRIVER RGLTR 1A 14WSON
- Quantity:
- Payment:
- Shipping:
Inventory:1,535
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Product details
Overview
LM3551SDX from Texas Instruments is a 1.25MHz fixed-frequency current-mode step-up DC/DC white LED driver with dual integrated low-side NFETs, delivering up to 1A total output current from 2.7V–5.5V input for flash/torch applications in camera phones and digital still cameras. It features independent torch/flash/shutdown modes, flash timeout protection via external capacitor on FTO pin, and over-voltage protection with 12.4V typical trip point.
For engineers reviewing the LM3551SDX datasheet, LM3551SDX pinout, LM3551SDX application, or LM3551SDX equivalent, key selection criteria include its 14-pin WSON (4mm × 4mm) package, dual-FET architecture enabling simultaneous torch + flash current control, programmable soft-start via SS pin, shutdown logic (high-active SD), and compatibility with high-current white LEDs such as Lumileds LXCL-PWF1 and Sharp GM5BW05340A.
Technical Context
The LM3551SDX implements a current-mode PWM boost converter with 1.25MHz constant switching frequency and 92.5% maximum duty cycle, using an internal 0.165Ω RDSON-SW power switch. Its error amplifier has 135µmho transconductance and 135V/V voltage gain, referenced to a tightly regulated 1.265V FB voltage.
It integrates two dedicated low-side NFETs-FET-T (0.98Ω RDSON, ≤200mA continuous) for torch mode and FET-F (0.36Ω RDSON, ≤500mA pulsed) for flash mode-with independent current-setting resistors RT and RF. Flash timeout is implemented via 1.4µA IFTO current charging CFTO to 1.16V trip threshold.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.7V to 5.5V - supports full Li-ion battery range (3.0V–4.2V) without brownout or overvoltage stress |
| Max Output Current | 1A total - sum of torch (via FET-T) and flash (via FET-T + FET-F) currents, enabling high-brightness LED operation |
| Switching Frequency | 1.25MHz (typ.) - enables use of small 4.7µH inductors and low-ESR ceramic capacitors (CIN ≥10µF, COUT ≥10µF) |
| FB Reference Voltage | 1.265V (typ.) - sets LED current accuracy; used with RT and RF to program torch/flash levels per I = 1.265V / Rext |
| OVP Threshold | 12.4V (typ.) - protects output stage during open-LED or feedback fault; auto-recovery at 10.6V |
| Flash Timeout Trip | 1.16V (typ.) on FTO pin - limits flash pulse duration via external CFTO; disable by grounding FTO |
| Shutdown Current | 2.55µA (typ.) - ultra-low quiescent draw in SD-high state, critical for battery-powered standby |
| Thermal Shutdown | 140°C (typ.) - internal protection engages before junction damage; resumes at 120°C |
Pinout & Package
LM3551SDX is housed in a 14-pin WSON package (4mm × 4mm, non-pullback, exposed thermal pad). Pin numbering follows TI's NHL0014B outline with die-attach pad (DAP) connected to GND for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 9) | Power Input | Accepts 2.7V–5.5V supply; requires ≥10µF low-ESR ceramic input capacitor for stability |
| T/F (Pin 13) | Mode Control | Logic-low = Torch Mode (FET-T enabled); logic-high = Flash Mode (FET-T + FET-F enabled) |
| SW (Pin 8) | Switch Node | Connects to boost inductor and Schottky diode anode; handles up to 20V peak during OVP events |
| OVP (Pin 10) | Over-Voltage Sense | Monitors output via resistor divider; grounding disables OVP (not recommended) |
| SD (Pin 5) | Shutdown Input | High = shutdown (2.55µA IQ); internal 1.2MΩ pull-up to VIN ensures default-off state |
| FTO (Pin 12) | Flash Timeout | Sinks 1.4µA to charge external CFTO; voltage ≥1.16V forces immediate FET/SW disable |
| SS (Pin 11) | Soft-Start Control | Sinks 11.5µA to charge external CSS; controls ramp rate of internal reference to limit inrush |
| FB (Pin 4) | Current Sense Feedback | Compares voltage across RT/RF to 1.265V reference; determines LED current magnitude |
| FET-T (Pin 14) | Torch FET Drain | Connects to cathode of torch-path LED; 0.98Ω RDSON supports ≤200mA continuous current |
| FET-F (Pin 2) | Flash FET Drain | Connects to cathode of flash-path LED; 0.36Ω RDSON supports ≤500mA pulsed current |
| GND (Pins 1,7,DAP) | Ground Return | Analog/digital ground common point; DAP must be soldered for thermal performance (θJA = 37.3°C/W) |
| AGND (Pin 6) | Analog Ground | Reference for VC, CFTO, CSS; must connect to GND via low-impedance trace to minimize noise coupling |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent FET outputs | Enables true separation of torch (continuous, low-power) and flash (pulsed, high-current) paths without shared current-limiting compromises |
| Programmable flash timeout | External CFTO sets precise flash duration (e.g., 1µF → ~830ms); prevents LED thermal damage during controller faults |
| True load disconnect in shutdown | Both FET-T and FET-F fully turn off; eliminates leakage paths to GND, reducing system standby current |
| Integrated OVP with auto-recovery | Clamps output at 12.4V and cycles SW on/off until fault clears - avoids destructive latch-up during open-LED conditions |
| 1.25MHz constant-frequency PWM | Ensures predictable EMI spectrum; simplifies filtering and allows compact magnetics vs. variable-frequency alternatives |
Applications
| White LED Camera Flash | Cellular Camera Phone Flash |
|---|---|
Use Scenario: High-intensity, short-duration illumination for smartphone rear/front cameras during low-light capture. IC Role / Device Role / Timing Role: LM3551SDX acts as the primary flash driver, regulating 700mA+ pulsed current through Lumileds LXCL-PWF1 via FET-F while managing thermal safety. Use Value: Delivers consistent luminance across Li-ion battery discharge (3.0V–4.2V) with flash timeout preventing LED overheating during software timing errors. | Use Scenario: Dual-mode lighting in compact mobile handsets requiring both flashlight (torch) and photo/video flash functions. IC Role / Device Role / Timing Role: LM3551SDX provides independent current control: FET-T drives 200mA torch mode; FET-T+FET-F drive 1A flash mode, selected via T/F pin logic level. Use Value: Eliminates need for separate torch/flash ICs; reduces BOM count and PCB area while maintaining precise brightness calibration per mode. |
| DSC (Digital Still Camera) Flash | PDA Camera Flash |
Use Scenario: Compact portable cameras needing reliable flash performance with minimal power supply interaction. IC Role / Device Role / Timing Role: LM3551SDX serves as the regulated boost source, stepping up single-cell battery voltage to drive high-Vf white LEDs (≥3.2V) at controlled current. Use Value: 1.25MHz switching enables use of tiny 4.7µH inductors and 10µF MLCCs, supporting ultra-thin DSC form factors without efficiency penalty. | Use Scenario: Legacy PDA devices with integrated VGA/MegaPixel cameras requiring robust flash capability within tight thermal envelopes. IC Role / Device Role / Timing Role: LM3551SDX manages LED current regulation and thermal safety via integrated OVP, UVP, and thermal shutdown - no external supervision needed. Use Value: Reduces firmware complexity by offloading flash timing, current limiting, and fault recovery to hardware, extending battery life in always-on PDA designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar white LED flash driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM3552SDX | Replaces SD pin with EN pin (active-high enable); identical analog functionality, same pinout except SD→EN mapping | Requires inverted logic control signal; not drop-in compatible with LM3551SDX firmware/hardware without signal inversion | Select LM3552SDX only when system-level enable logic is active-high and board layout accommodates EN pin routing |
| TPS61310DSQR | Single-FET boost driver (no dual torch/flash FETs); max 1.5A switch current but no integrated load disconnect FETs | Requires external MOSFETs and gate drivers for torch/flash separation; increases BOM and layout complexity | Choose TPS61310DSQR only when higher peak current (>1A) is required and dual-FET integration is not essential |
Compared with LM3552SDX, the LM3551SDX offers native high-active shutdown control ideal for systems with open-drain or level-shifted logic, while TPS61310DSQR trades integrated dual-FET simplicity for higher switch current headroom at the cost of added external components and design effort.
Availability
LM3551SDX is available at Aetrix Electronics and suitable for cellular camera phone flash, digital still camera (DSC) flash, and PDA camera flash applications requiring stable component supply, long-term lifecycle support, and guaranteed authentic Texas Instruments sourcing.
Supply support for LM3551SDX 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 connectivity technologies, with decades of expertise in power management ICs for portable electronics.
The LM3551SDX belongs to TI's white LED flash driver product line, engineered specifically for high-efficiency, thermally safe, dual-mode (torch + flash) illumination in space-constrained mobile imaging systems.
FAQ
What is the function of the SD pin on the LM3551SDX?
The SD (Shutdown) pin on the LM3551SDX is a logic-input control terminal where a high voltage (≥1.2V) places the device into ultra-low-power shutdown mode, drawing only 2.55µA. A low voltage (≤0.3V) enables normal operation. An internal 1.2MΩ pull-up to VIN ensures default shutdown if left unconnected, enhancing system safety during power-up sequencing.
How does the LM3551SDX implement flash timeout protection?
The LM3551SDX implements flash timeout protection by sinking a precise 1.4µA current from the FTO pin to charge an external capacitor (CFTO). When the voltage across CFTO reaches 1.16V, the internal timeout circuit disables both FET-T and FET-F, plus the main SW FET, turning off the LED. The part remains disabled until SD is pulled high or T/F is pulled low, ensuring fail-safe flash duration control.
Can the LM3551SDX drive both torch and flash LEDs simultaneously?
No - the LM3551SDX does not drive torch and flash LEDs simultaneously. Torch mode (T/F = low) activates only FET-T; flash mode (T/F = high) activates both FET-T and FET-F. The device supports either continuous low-power illumination (torch) or high-current pulsed illumination (flash), but not concurrent operation of both paths, preserving thermal integrity and current accuracy.
What is the recommended output capacitor for the LM3551SDX when driving a Lumileds LXCL-PWF1?
When driving the Lumileds LXCL-PWF1, the LM3551SDX requires a minimum 10µF low-ESR ceramic output capacitor (X7R/X5R dielectric, 16V rating). This value ensures stable regulation under 700mA flash loads and maintains output ripple below 50mV peak-to-peak. Larger values (e.g., 22µF) further reduce ripple but must retain low ESR (<20mΩ) to avoid loop instability.
Does the LM3551SDX require external compensation components?
Yes - the LM3551SDX requires external RC/CC network on the VC pin for loop stability. A typical configuration uses RC = 10kΩ and CC = 4.7nF for Lumileds LEDs, forming a pole-zero pair that compensates for output capacitor ESR effects and right-half-plane zero. Omitting or mis-sizing these components risks oscillation or poor transient response during LED current steps.
LM3551SDX Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 14-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):
- 5.5V
- Voltage - Output:
- -
- Current - Output / Channel:
- 1A (Flash)
- Frequency:
- 1.25MHz
- Dimming:
- -
- Applications:
- Camera Flash
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-WSON (4x4)
LM3551SDX FAQ
1.How can I place an order for LM3551SDX through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3551SDX 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 LM3551SDX reliable?
The price and inventory of LM3551SDX are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM3551SDX is usually 5 days.
3.What payment methods are accepted for LM3551SDX?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3551SDX transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3551SDX?
LM3551SDX orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3551SDX 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 LM3551SDX?
For technical support, including LM3551SDX datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3551SDX requirements.
6.How does Aetrix verify that LM3551SDX is sourced from the original manufacturer or authorized distributors?
All LM3551SDX 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 LM3551SDX meets industry standards.
7.What is the process for return or replacement of LM3551SDX?
All LM3551SDX units undergo pre-shipment inspection (PSI). If there is an issue with LM3551SDX, 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 LM3551SDX part is unused and in its original packaging.
Return procedure for LM3551SDX:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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