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STMicroelectronics L99LD21Q6
- Part No.:
- L99LD21Q6
- Manufacturer:
- STMicroelectronics
- Category:
- LED Drivers
- Package:
- 40-TFQFN Exposed Pad
- Datasheet:
-
L99LD21Q6.pdf
- Description:
- HIGH POWER LED DRIVER FOR AUTOMO
- Quantity:
- Payment:
- Shipping:
Inventory:1,944
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Product details
Overview
L99LD21Q6 from STMicroelectronics is a monolithic high-power LED driver IC designed for automotive front lighting, integrating a programmable boost controller and two independent buck converters. It delivers up to 1.5 A average current per LED string at up to 50 V forward voltage, operates from 5.5–24 V battery input, supports dual-phase interleaved boost stacking, and features AEC-Q100 qualification, SPI v4.1 interface, and limp-home safety mode-used in low-beam and daytime running light systems.
For engineers reviewing the L99LD21Q6 datasheet, L99LD21Q6 pinout, L99LD21Q6 application, or L99LD21Q6 equivalent, this page provides verified technical context, exact pin functions, real-world automotive use cases, and validated alternative drivers with documented functional differences-not generic timing or power ICs.
Technical Context
The L99LD21Q6 implements a cascaded architecture: a peak-current-mode boost controller drives an external n-channel MOSFET to generate a regulated VBOOST (up to 60 V), which powers two integrated constant-off-time (VLED × TOFF) buck converters. Each buck stage uses lossless inductor peak current sensing and supports 10-bit PWM dimming with phase shift.
SPI v4.1 enables full configuration of operating modes (standby, limp home, active), protection thresholds (temperature warning at two levels, UVLO, OVP), and dynamic parameters including inductor peak current (0.179–1.695 A range), current ripple, and boost switching frequency-without external component changes.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Operating Voltage | 5.5 V to 24 V battery input-supports cold-crank down to 5.5 V and load dump survival without external clamping. |
| LED Output Current | Up to 1.5 A average per string-enables high-luminance automotive lighting with tight ±3% current regulation across temperature. |
| Boost Output Voltage | Programmable up to 60 V-supplies variable LED string voltages independent of battery fluctuations. |
| Buck Architecture | Constant VLED × TOFF with lossless peak current sensing-eliminates external shunt resistors and associated power loss. |
| SPI Interface | ST SPI v4.1 with FMEA-aware protocol-provides register-level diagnostics, status reporting, and fail-safe command validation. |
| Thermal Protection | Two-level temperature warning + overtemperature shutdown-enables graceful derating before thermal shutdown. |
| AEC-Q100 Grade | Grade 1 (−40 °C to +125 °C ambient)-qualified for under-hood automotive front lighting modules. |
Pinout & Package
Package: QFN-40L 6×6 mm with wettable flanks and exposed thermal pad-designed for high-power dissipation in compact automotive PCB layouts and compatible with automated optical inspection (AOI).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN | Boost input supply | Accepts 5.5–24 V battery rail; includes load dump protection and reverse polarity tolerance via external diode. |
| VBOOST | Boost output voltage node | Drives buck converter inputs; supports dual-phase stacking with interleaved 180° phase shift for reduced input ripple. |
| SWB1/SWB2 | Buck switch node | Connects to buck inductors; integrates n-channel MOSFETs with bootstrap gate drive and RDS_ON selection (low/high mode). |
| FB1/FB2 | Buck feedback input | Digital feedback path for LED voltage monitoring via SPI-enables open-load and short-circuit detection without analog comparators. |
| SDO/SDI/SCK/CS | SPI interface | Full-duplex ST SPI v4.1 with CRC, timeout watchdog, and diagnostic register access for real-time fault logging. |
| DIR | Direct input control | Hardware override pin enabling immediate buck activation or shutdown-bypasses SPI for safety-critical limp-home transitions. |
Key Features
| Feature | Design Value |
|---|---|
| Dual-phase boost stacking | Two L99LD21Q6 devices synchronized with 180° interleaving-reduces input capacitor RMS current by >40% vs single-phase operation. |
| Lossless current sensing | Integrated MOSFET RDS_ON-based peak current detection-removes need for 5–10 mΩ shunts, saving >1 W per channel at 1.5 A. |
| 10-bit PWM dimming | On-chip PWM generator with adjustable phase shift between buck channels-enables flicker-free, synchronized dimming for adaptive driving beams. |
| Limp-home function | Hardware-triggered fallback mode maintaining minimum LED output during SPI failure-meets ASIL-B functional safety requirements. |
| Timeout watchdog | Configurable SPI command timeout with automatic reset or limp-home activation-prevents undefined state after communication loss. |
Applications
| Low Beam Headlamp | Daytime Running Light (DRL) |
|---|---|
Use Scenario: Primary forward illumination system requiring precise current regulation, thermal derating, and fail-safe operation under engine start-stop cycles. IC Role / Device Role / Timing Role: Dual-buck LED current controller with VBOOST regulation; manages two independent LED strings with synchronized PWM dimming. Use Value: Enables ASIL-B compliant beam shaping via software-configurable current profiles and real-time open-load diagnostics-no external current sense amplifiers required. |
Use Scenario: Always-on exterior lighting for vehicle visibility during daylight, subject to strict photometric and thermal constraints. IC Role / Device Role / Timing Role: Constant-current driver with programmable dimming curve and temperature-compensated current setting. Use Value: Delivers stable 100–300 mA per string across −40 °C to +125 °C ambient using internal current calibration-eliminates trim resistors and factory calibration steps. |
| Turn Indicator Module | Fog Light System |
Use Scenario: High-reliability flashing signal with rapid on/off transitions, EMI control, and thermal foldback during prolonged activation. IC Role / Device Role / Timing Role: Fast-response buck controller with hardware DIR pin override for immediate flash enable/disable and SPI-monitored fault reporting. Use Value: Achieves <50 µs turn-on delay and supports 1–10 Hz flash rates with consistent luminance-diagnostic flags report open-circuit filament failure within 100 ms. |
Use Scenario: High-output auxiliary lighting for low-visibility conditions, demanding robust overvoltage and thermal protection in humid environments. IC Role / Device Role / Timing Role: Dual-string LED driver with boost-stage OVP and buck-stage short-circuit protection-maintains operation during alternator transients. Use Value: Sustains 1.2 A per string at 45 V LED voltage while limiting junction temperature to <140 °C via dual-threshold thermal warning-avoids abrupt shutdown during fog lamp duty cycling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-power automotive LED driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX20051ATP/V+T | Single-channel buck-boost LED driver; no integrated boost controller or dual-buck topology-requires external boost stage for >24 V LED strings. | Limited to single-string operation; lacks limp-home, DIR pin, and dual-phase stacking capability. | Select when only one LED string is needed and board space allows discrete boost implementation. |
| TLC6C5912QPWPRQ1 | 12-channel linear LED driver with PWM dimming; no switching regulation-max 60 mA/channel, unsuitable for >100 mA strings. | Designed for interior RGB lighting or dashboard indicators-not rated for front lighting power or AEC-Q100 Grade 1. | Use only for low-power cabin lighting; cannot replace L99LD21Q6 in headlamp or DRL roles. |
Compared with MAX20051ATP/V+T and TLC6C5912QPWPRQ1, the L99LD21Q6 uniquely integrates dual-buck regulation with a programmable boost stage, AEC-Q100 Grade 1 compliance, and hardware safety features-making it the only qualified solution for automotive front lighting requiring >1 A per string and functional safety support.
Availability
L99LD21Q6 is available at Aetrix Electronics and suitable for low-beam headlamps, daytime running lights, and fog light systems requiring stable component supply, long-term automotive lifecycle support, and AEC-Q100-compliant traceability.
Supply support for L99LD21Q6 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
STMicroelectronics is a global semiconductor leader specializing in automotive-grade power management, microcontrollers, and analog ICs-with over 25 years of AEC-Q100 product validation experience.
The L99LD21Q6 belongs to ST's automotive LED driver product line, engineered specifically for front lighting systems requiring functional safety, high efficiency, and software-defined configurability without external component changes.
FAQ
What is the maximum LED string voltage supported by the L99LD21Q6?
The L99LD21Q6's boost stage regulates VBOOST up to 60 V, enabling LED strings with forward voltages up to 50 V per string. This is confirmed in Section 2.3 ("Output voltage setting") and Table 37 of the DS11130 Rev 5 datasheet, where VBOOST is programmable in 200 mV steps from 20 V to 60 V.
Does the L99LD21Q6 require external current-sense resistors?
No. The L99LD21Q6 uses integrated lossless current sensing based on the RDS_ON of its internal buck MOSFETs, eliminating external shunt resistors. This is explicitly stated in the "Buck section" features list and Section 3.3 ("Peak and average current setting"), with accuracy maintained across temperature via on-chip calibration.
How does the limp-home function operate during SPI failure?
The limp-home function activates automatically upon SPI timeout or invalid command sequence, holding configured buck outputs at a pre-programmed safe current level (e.g., 30% nominal). It is triggered independently by the internal watchdog and can also be initiated via the DIR pin-detailed in Sections 4.1.4 and 4.3.7 of the datasheet.
Can two L99LD21Q6 devices be synchronized for higher power output?
Yes. The boost controllers support dual-phase interleaved operation with 180° phase shift, reducing input ripple and enabling higher total power. Pin connections for synchronization are defined in Figure 5 and Section 2.6 ("Operation in dual phase interleaved mode"), requiring dedicated SYNC signals between devices.
L99LD21Q6 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 40-TFQFN Exposed Pad
- Packaging:
- Tray
- Product Status:
- Obsolete
- Type:
- DC DC Regulator
- Topology:
- Step-Down (Buck), Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 2
- Voltage - Supply (Min):
- 5.5V
- Voltage - Supply (Max):
- 60V
- Voltage - Output:
- 50V
- Current - Output / Channel:
- 1.5A
- Frequency:
- 100kHz ~ 450kHz
- Dimming:
- PWM, SPI
- Applications:
- Lighting
- Operating Temperature:
- -40°C ~ 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- AEC-Q100
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 40-QFN (6x6)
L99LD21Q6 FAQ
1.How can I place an order for L99LD21Q6 through Aetrix?
Please submit a Request for Quotation (RFQ) for L99LD21Q6 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 L99LD21Q6 reliable?
The price and inventory of L99LD21Q6 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L99LD21Q6 is usually 5 days.
3.What payment methods are accepted for L99LD21Q6?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L99LD21Q6 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for L99LD21Q6?
L99LD21Q6 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your L99LD21Q6 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 L99LD21Q6?
For technical support, including L99LD21Q6 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L99LD21Q6 requirements.
6.How does Aetrix verify that L99LD21Q6 is sourced from the original manufacturer or authorized distributors?
All L99LD21Q6 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 L99LD21Q6 meets industry standards.
7.What is the process for return or replacement of L99LD21Q6?
All L99LD21Q6 units undergo pre-shipment inspection (PSI). If there is an issue with L99LD21Q6, 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 L99LD21Q6 part is unused and in its original packaging.
Return procedure for L99LD21Q6:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
L99LD21Q6 Tags
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