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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > LED Drivers

STMicroelectronics L99LD21Q6TR

Name: L99LD21Q6TR
Brand: STMicroelectronics
SKU: L99LD21Q6TR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L99LD21Q6TR

Manufacturer:: STMicroelectronics

Category:: LED Drivers

Package:: 40-TFQFN Exposed Pad

Datasheet:: L99LD21Q6TR.pdf

Description:: IC LED DRVR RGLTR PWM 1.5A 40QFN

Quantity:: RFQ Add To RFQ list

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Product details

Overview

L99LD21Q6TR from STMicroelectronics is an AEC-Q100 qualified monolithic LED driver IC for automotive front lighting, integrating a programmable boost controller (5.5–24 V input, up to 60 V output) and two independent buck converters with lossless current sensing, delivering up to 1.5 A average LED current per channel for low/high beam and DRL applications.

For engineers reviewing the L99LD21Q6TR datasheet, L99LD21Q6TR pinout, L99LD21Q6TR application, or L99LD21Q6TR equivalent, this page delivers verified technical context, SPI-configurable current/voltage control, dual-phase boost stacking capability, thermal warning/shutdown thresholds, and diagnostic feedback via ST SPI v4.1 - all critical for functional safety-compliant headlamp system design.

Technical Context

The device 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 features programmable inductor peak current (0.179–1.695 A range), adjustable current ripple, and 10-bit PWM dimming with phase shift.

Functional safety is embedded via timeout watchdog, limp-home mode, dual temperature warning thresholds (T_WARN1/T_WARN2), overtemperature shutdown, and comprehensive SPI-accessible diagnostics including LED open/short detection, battery UVLO, and feedback failure protection - all compliant with ASIL-B requirements for front lighting.

Key Specifications

Parameter	Value and Actual Design Meaning
Operating Voltage	5.5 V to 24 V battery input; supports load dump transients per ISO 7637-2.
Boost Output Voltage	Up to 60 V; programmable via SPI; supplies dual buck inputs independently.
LED Current Accuracy	±3% typical average current per channel; achieved via lossless peak current sensing and VLED × TOFF architecture.
Buck Switching	Constant off-time (COT) control; 10-bit PWM dimming resolution; phase-shifted dual-channel operation.
Thermal Protection	Two programmable temperature warning thresholds + automatic overtemperature shutdown at T_J ≥ 175 °C.
SPI Interface	ST SPI v4.1 protocol; supports diagnostics readback, register configuration, and FMEA-aware command validation.
Package	QFN-40L 6×6 mm with wettable flanks and exposed thermal pad; R_θJA = 28.5 °C/W (4-layer PCB).

Pinout & Package

QFN-40L 6×6 mm package with wettable flanks and exposed thermal pad for enhanced thermal dissipation in automotive under-hood environments. Pin numbering follows standard QFN convention (pin 1 marked by dot).

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 node	Drives external N-MOSFET gate; provides regulated high-voltage rail (≤60 V) to buck converter inputs.
BK1OUT / BK2OUT	Buck output terminals	Drive LED strings directly; each supports up to 1.5 A average current with integrated low-R_DS(on) N-MOSFETs.
CS1 / CS2	Current sense inputs	Enable lossless inductor current monitoring; no external shunt required for peak/average current regulation.
SDI / SDO / SCLK / CS	SPI interface signals	ST SPI v4.1 compliant; support full-duplex register access, status reporting, and fault logging with CRC validation.
DIN1 / DIN2	Direct input controls	Hardware override pins for buck activation; enable fast fail-safe response independent of SPI communication.
WDI / WDO	Watchdog interface	Timeout watchdog input/output; triggers limp-home mode on missed refresh; supports ASIL-B functional safety path.

Key Features

Feature	Design Value
Dual-phase boost stacking	Two L99LD21Q6TR devices can be interleaved 180° to halve input current ripple and scale power for high-beam/fog light systems.
Lossless current sensing	Integrated MOSFET R_DS(on)-based sensing eliminates external shunt resistors, reducing BOM cost and thermal losses.
VLED × TOFF architecture	Stabilizes LED current across wide forward voltage variation (e.g., cold vs. hot LED strings) without feedback loop compensation.
Programmable thermal thresholds	Two independent warning levels (T_WARN1, T_WARN2) allow graded derating before shutdown - critical for thermal management in sealed headlamps.
Limp-home function	On critical fault (e.g., open LED, overtemp), reduces output to safe minimum brightness while maintaining illumination - meets UNECE R149 requirements.

Applications

Low Beam Headlamp

High Beam Headlamp

Use Scenario: Primary forward illumination during nighttime driving, requiring precise current regulation and thermal robustness.

IC Role / Device Role / Timing Role: Dual-buck driver delivers stable 700 mA–1.2 A per LED string; boost stage maintains VBOOST > V_fwd across battery voltage sag and temperature drift.

Use Value: ±3% current accuracy ensures consistent lumen output; limp-home preserves minimum legal illumination during partial failure.

Use Scenario: Intermittent high-intensity illumination for long-range visibility, demanding dynamic current scaling and thermal headroom.

IC Role / Device Role / Timing Role: Dual-phase stacked boost enables higher power delivery; 10-bit PWM dimming supports adaptive driving beam (ADB) modulation.

Use Value: Interleaved operation cuts input ripple by 50%, easing EMI filter design; programmable peak current supports multiple LED configurations.

Daytime Running Light (DRL)

Turn Indicator Module

Use Scenario: Always-on daytime illumination with strict power efficiency and ambient temperature resilience.

IC Role / Device Role / Timing Role: Buck converters operate in continuous conduction mode at low duty cycle; standby current < 50 µA minimizes parasitic drain.

Use Value: Lossless sensing and COT control maintain efficiency >92% at 100–300 mA; thermal warning prevents luminous flux degradation in enclosed housings.

Use Scenario: Flashing signal with rapid on/off transitions, requiring deterministic fault response and EMI-controlled switching.

IC Role / Device Role / Timing Role: Direct input (DIN) pins enable hardware-triggered flash timing; short-circuit/open-load detection isolates faults within 2 µs.

Use Value: SPI-diagnostic feedback confirms LED integrity before each flash cycle; limp-home sustains 10% brightness if one channel fails - meeting FMVSS 108 compliance.

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; requires external inductor and MOSFET for boost stage.	Targeted at mid-power rear lighting; lacks dual-buck integration and limp-home functionality.	Select when system-level flexibility outweighs integration - e.g., mixed front/rear lighting with shared boost rail.
TLC6C5912QPWRQ1	12-channel linear LED driver; no switching topology; limited to ≤60 mA/channel; no thermal warning thresholds.	Designed for interior RGB ambient lighting; unsuitable for high-power front lighting due to efficiency and thermal constraints.	Choose only for non-safety-critical, low-current applications where PWM dimming precision matters more than power density.

Compared with MAX20051ATP/V+T and TLC6C5912QPWRQ1, the L99LD21Q6TR uniquely integrates dual-buck + programmable boost in one AEC-Q100 package with ASIL-B-ready diagnostics, enabling compact, thermally robust front lighting designs without external power stage components or safety software overhead.

Availability

L99LD21Q6TR is available at Aetrix Electronics and suitable for automotive front lighting, adaptive driving beam (ADB), and functional safety-compliant headlamp systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for L99LD21Q6TR 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 analog, power, and microcontroller solutions with deep expertise in functional safety and AEC-Q100 qualification.

The L99LD21 belongs to ST's Automotive LED Driver product line, engineered specifically for ASIL-B-compliant front lighting systems requiring high integration, thermal resilience, and real-time diagnostics - not general-purpose LED control.

FAQ

What is the maximum allowable LED string voltage supported by L99LD21Q6TR?

The boost stage regulates up to 60 V output, enabling LED strings with combined forward voltage up to 50 V per buck channel. This accommodates multi-chip LED arrays used in modern low/high beam modules, provided VBOOST exceeds total V_fwd plus buck dropout margin (typically ≥2 V). The VLED × TOFF architecture maintains current accuracy even as V_fwd varies with temperature.

How does the limp-home function activate and what output level does it provide?

Limp-home activates automatically upon critical fault detection - such as overtemperature shutdown, open LED load, or watchdog timeout - and forces both buck outputs to a preconfigured reduced current level (programmable via SPI register CR#3 bit[7:6]). This level is typically set to 10–20% of nominal current, ensuring minimum legal illumination while preventing complete beam loss during vehicle service.

Can L99LD21Q6TR drive LEDs with different forward voltages on BK1OUT and BK2OUT simultaneously?

Yes. Each buck converter operates independently with its own VLED × TOFF constant, allowing distinct LED string configurations - e.g., 35 V low-beam + 42 V high-beam - as long as VBOOST exceeds the higher V_fwd plus buck conduction drop. The boost output is shared, but buck current regulation, PWM dimming, and diagnostics are fully decoupled per channel.

Is external current sense resistor required for accurate LED current regulation?

No. The L99LD21Q6TR uses integrated MOSFET R_DS(on) for lossless current sensing on both buck channels. Peak inductor current is measured directly across the internal switch, eliminating external shunts, associated power loss, PCB area, and calibration drift - confirmed in Section 3.3 and Table 39 of DS11130 Rev 5.

L99LD21Q6TR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 40-TFQFN Exposed Pad

Packaging:: Tape & Reel (TR)

Product Status:: Active

Type:: DC DC Regulator

Topology:: Buck, Boost

Internal Switch(s):: Yes

Number of Outputs:: 2

Voltage - Supply (Min):: 5.5V

Voltage - Supply (Max):: 24V

Voltage - Output:: 50V

Current - Output / Channel:: 1.5A

Frequency:: 100kHz ~ 450kHz

Dimming:: PWM

Applications:: Lighting

Operating Temperature:: -40°C ~ 150°C (TJ)

Grade:: Automotive

Qualification:: AEC-Q100

Mounting Type:: Surface Mount

Supplier Device Package:: 40-QFN (6x6)

L99LD21Q6TR FAQ

1.How can I place an order for L99LD21Q6TR through Aetrix?

Please submit a Request for Quotation (RFQ) for L99LD21Q6TR 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 L99LD21Q6TR reliable?

The price and inventory of L99LD21Q6TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L99LD21Q6TR is usually 5 days.

3.What payment methods are accepted for L99LD21Q6TR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L99LD21Q6TR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L99LD21Q6TR?

L99LD21Q6TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L99LD21Q6TR 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 L99LD21Q6TR?

For technical support, including L99LD21Q6TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L99LD21Q6TR requirements.

6.How does Aetrix verify that L99LD21Q6TR is sourced from the original manufacturer or authorized distributors?

All L99LD21Q6TR 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 L99LD21Q6TR meets industry standards.

7.What is the process for return or replacement of L99LD21Q6TR?

All L99LD21Q6TR units undergo pre-shipment inspection (PSI). If there is an issue with L99LD21Q6TR, 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 L99LD21Q6TR part is unused and in its original packaging.

Return procedure for L99LD21Q6TR:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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