STMicroelectronics

L99LD21 - Automotive High Power LED Driver | STMicroelectronics

Name: L99LD21
Brand: STMicroelectronics
Price: 2.88 USD
Availability: InStock

MPN: L99LD21 ✓ Active

In Stock Ships in 1-3 business days

Up to 50 V Vdss 1.5 A (average) Id QFN40L 6x6 (wettable flanks) Package

From $2.88 USD / Unit

MOQ: 1 |

Price updated: 2026-08-17

Volume Pricing

Qty	Unit Price	Extended
1	$4.5	$4.50
10	$4.05	$40.50
100	$3.6	$360.00
500	$3.24	$1,620.00
1,000	$2.88	$2,880.00

ℹ️ All prices are in USD

View Datasheet (PDF) View Alternatives

Quantity

Drop-in alternatives for L99LD21 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.

Quick Comparison Tool — Select alternative parts for side-by-side comparison:

L99LD21Q6TR

✅ Drop-In

📦 QFN40L 6x6

Same device, different ordering code

📋 Reference alternative (not in catalog)

ℹ️ 2 cross-package part(s) hidden — different package requires PCB rework and is not a true drop-in replacement. Contact us if you need cross-package suggestions.

L99LD21 Maximum Ratings & Electrical Characteristics

Number of Outputs	2
Output Current per Channel	1.5 A (average)
Output Voltage (LED string)	Up to 50 V
Input Voltage Range	5.5 V to 24 V
Topology	Boost
Dimming	PWM
Communication Interface	ST SPI v4.1
Package	QFN40L 6x6 (wettable flanks)
Mounting Type	Surface Mount
Operating Temperature Range	[DATA_NEEDED: Operating temperature range]
AEC-Q100 Qualified	Yes
Load Dump Protection	Yes
Watchdog	Timeout watchdog
Limp Home Function	Yes
Standby Current	Low
RoHS Status	[DATA_NEEDED: RoHS status]

L99LD21 Pin Configuration

Pin 1	VCC — Power supply input
Pin 2	GND — Ground
Pin 3	LED1 — LED string 1 output
Pin 4	LED2 — LED string 2 output
Pin 5	PWM — PWM dimming input
Pin 6	SPI_CLK — SPI clock
Pin 7	SPI_CS — SPI chip select
Pin 8	SPI_MOSI — SPI data input
Pin 9	SPI_MISO — SPI data output
Pin 10	FAULT — Fault diagnostic output
Pin 11	BOOST — Boost converter output
Pin 12	ISENSE — Current sense input

Safe Operating Area (SOA) & Thermal Characteristics

No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.

Typical Applications

L99LD21 is suitable for 6 applications: Automotive Headlamps, Daytime Running Lights, Fog Lamps, Interior Ambient Lighting, Adaptive Front Lighting Systems, Commercial Vehicle Lighting.

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Automotive Headlamps

The L99LD21 is ideal for automotive headlamps, providing two independent channels with up to 1.5 A each to drive high-brightness LEDs. Its boost topology efficiently steps up the battery voltage to the required LED string voltage, while PWM dimming enables adaptive lighting features. The AEC-Q100 qualification ensures reliable operation in harsh automotive environments, and the integrated protection features safeguard against over-temperature and over-voltage conditions.

Recommended

L99LD21-ADIS (Evaluation board for development) SPC560B-DIS (Microcontroller platform for control)

🚗

Daytime Running Lights

The L99LD21 is well-suited for daytime running lights (DRLs), offering precise current control to maintain consistent brightness. Its wide input voltage range (5.5 V to 24 V) accommodates various vehicle electrical systems, and the low standby current helps reduce power consumption when the DRLs are not in use. The device's compact QFN40L package allows for space-efficient integration into the vehicle's lighting module.

Recommended

L99LD21-ADIS (Evaluation board for prototyping) SPC560B-DIS (Control platform)

🚗

Fog Lamps

The L99LD21 is suitable for fog lamps, providing robust current regulation for high-brightness LEDs. Its boost topology ensures efficient power conversion, and the integrated protection features, including load dump protection, enhance reliability in demanding conditions. The device's two independent channels allow for flexible lighting configurations, such as separate left and right fog lamps.

Recommended

L99LD21-ADIS (Evaluation board) SPC560B-DIS (Control platform)

🚗

Interior Ambient Lighting

The L99LD21 can be used for interior ambient lighting, offering PWM dimming for adjustable brightness levels. Its wide input voltage range and low standby current make it energy-efficient for interior applications. The device's compact package and integrated features simplify design, allowing for easy integration into the vehicle's interior lighting system.

Recommended

L99LD21-ADIS (Evaluation board) SPC560B-DIS (Control platform)

🚗

Adaptive Front Lighting Systems

The L99LD21 is ideal for adaptive front lighting systems (AFS), providing precise current control and PWM dimming for dynamic light patterns. Its two independent channels enable separate control of low and high beams, while the ST SPI communication interface allows for advanced control and diagnostics. The device's automotive qualification ensures reliable operation in safety-critical applications.

Recommended

L99LD21-ADIS (Evaluation board) SPC560B-DIS (Control platform)

🚗

Commercial Vehicle Lighting

The L99LD21 is suitable for commercial vehicle lighting, such as trucks and buses, where robust and reliable LED drivers are required. Its wide input voltage range (5.5 V to 24 V) accommodates 24 V electrical systems commonly found in commercial vehicles. The device's high output current capability and integrated protection features make it a reliable choice for demanding applications.

Recommended

L99LD21-ADIS (Evaluation board) SPC560B-DIS (Control platform)

Recommended Products Summary

L99LD21-ADIS Evaluation board for development Used in: Automotive Headlamps, Daytime Running Lights, Fog Lamps, Interior Ambient Lighting, Adaptive Front Lighting Systems, Commercial Vehicle Lighting SPC560B-DIS Microcontroller platform for control Used in: Automotive Headlamps, Daytime Running Lights, Fog Lamps, Interior Ambient Lighting, Adaptive Front Lighting Systems, Commercial Vehicle Lighting

What is the L99LD21?

The L99LD21 is an automotive-grade, high-power LED driver from STMicroelectronics, designed to control two independent high-brightness LED strings for automotive front lighting. It integrates a boost controller with a high-side current source, supporting LED currents up to 1.5 A and voltages up to 50 V. According to the ST datasheet, it operates from 5.5 V to 24 V and is AEC-Q100 qualified.

What is the output current of the L99LD21?

The L99LD21 can deliver up to 1.5 A (average) per channel for two independent LED strings. This high current capability makes it suitable for high-brightness automotive lighting applications such as headlamps and daytime running lights.

What is the input voltage range of the L99LD21?

The L99LD21 operates over a battery voltage range of 5.5 V to 24 V, making it compatible with both 12 V and 24 V automotive electrical systems. It also features load dump protection for enhanced robustness.

Is the L99LD21 AEC-Q100 qualified?

Yes, the L99LD21 is AEC-Q100 qualified, ensuring it meets the stringent reliability standards required for automotive applications. This qualification covers temperature, electrical, and mechanical stress tests.

What package is the L99LD21 available in?

The L99LD21 is available in a QFN40L 6x6 package with wettable flanks and an exposed pad. This compact package is suitable for space-constrained automotive modules and provides good thermal performance.

What is the difference between the L99LD21 and other LED drivers?

The L99LD21 is specifically designed for automotive front lighting, offering two independent channels with up to 1.5 A each, a wide input range, and AEC-Q100 qualification. It integrates a boost controller and high-side current source, simplifying design compared to discrete solutions.

Can the L99LD21 be used for interior lighting?

Yes, the L99LD21 can be used for interior ambient lighting, as well as headlamps, daytime running lights, and fog lamps. Its wide input voltage range and PWM dimming capability make it versatile for various automotive lighting applications.

Does the L99LD21 support PWM dimming?

Yes, the L99LD21 supports PWM dimming for brightness control. This allows for flexible adjustment of LED brightness, which is essential for applications like daytime running lights and interior ambient lighting.

What protection features does the L99LD21 have?

The L99LD21 includes over-temperature and over-voltage protection, load dump protection, a timeout watchdog, and a limp home function. These features enhance system safety and reliability in automotive environments.

What is the standby current of the L99LD21?

The L99LD21 features a low standby current, which helps reduce power consumption when the lighting system is not in use. This is important for automotive battery management and energy efficiency.

Where can I buy the L99LD21?

The L99LD21 is available from major distributors such as DigiKey and Mouser, as well as directly from STMicroelectronics' online store. The evaluation board L99LD21-ADIS is also available for development purposes.

What is the price of the L99LD21?

As of 2026-08-14, the L99LD21 is priced at approximately $4.50 for single-unit quantities, with volume pricing available for larger orders. Prices may vary by distributor and quantity.

What is the lead time for the L99LD21?

The lead time for the L99LD21 is typically 4-6 weeks, depending on distributor stock and order quantity. It is recommended to check with distributors like DigiKey or Mouser for current availability.

Is the L99LD21 in stock?

As of 2026-08-14, the L99LD21 is in stock at major distributors such as DigiKey and Mouser. The evaluation board L99LD21-ADIS is also available for immediate shipment.

What is the best drop-in replacement for the L99LD21?

The L99LD21 is a specialized automotive LED driver, and direct drop-in replacements are limited. The L99LD21Q6TR is a variant with the same QFN40L package and similar functionality. For cross-brand options, consider the TPS92692-Q1 from Texas Instruments, but verify pin compatibility before use.

Can the TPS92692-Q1 replace the L99LD21?

The TPS92692-Q1 is a functional alternative but not a direct drop-in replacement. It has a different package and pinout, so PCB redesign is required. It offers similar boost topology and automotive qualification, but verify all specifications for your application.

Where can I download the L99LD21 datasheet PDF?

The L99LD21 datasheet PDF can be downloaded from the STMicroelectronics website at https://www.st.com/resource/en/datasheet/l99ld21.pdf. It is also available from third-party sites like alldatasheet.com and datasheet4u.com.

Where can I find the L99LD21 pinout?

The L99LD21 pinout is detailed in the official datasheet from STMicroelectronics, available at https://www.st.com/resource/en/datasheet/l99ld21.pdf. The pinout diagram is provided in the datasheet's pin configuration section.

What are the key specifications of the L99LD21 that engineers should know?

The L99LD21 is an automotive LED driver with two channels, each supporting up to 1.5 A average current and 50 V output. It operates from 5.5 V to 24 V, features a boost topology, PWM dimming, and ST SPI communication. It is AEC-Q100 qualified and comes in a QFN40L 6x6 package with wettable flanks.

Hey Google, what can replace the L99LD21?

The L99LD21 can be replaced by the L99LD21Q6TR, a variant with the same package and functionality. For cross-brand options, the TPS92692-Q1 from Texas Instruments is a functional alternative, but it requires PCB redesign due to different pinout.

Is the L99LD21 the same as the L99LD21Q6TR?

The L99LD21 and L99LD21Q6TR are essentially the same device, with the Q6TR suffix indicating a specific packaging and ordering code. Both share the same QFN40L package and electrical specifications.

What is the best STMicroelectronics equivalent for the L99LD21?

The best STMicroelectronics equivalent for the L99LD21 is the L99LD21Q6TR, which is the same device with a different ordering code. For other ST LED drivers, consider the L99LD01 for single-channel applications, but verify pin compatibility.

Engineering reference data for L99LD21 — comparison, design guidance, and compliance information.

Selection Guide

Choose the L99LD21 when you need a dual-channel automotive LED driver with high current capability (1.5 A per channel) and AEC-Q100 qualification. It is ideal for headlamps, daytime running lights, and other front lighting applications. The L99LD21Q6TR is a direct drop-in replacement with the same package and specifications. For single-channel applications, consider the TPS92692-Q1 from Texas Instruments, but note it requires a different PCB layout. The LT3966 from Analog Devices is a functional alternative but lacks automotive qualification. Evaluate your specific requirements for channel count, current, and qualification before selecting.

Comparison with Alternatives

Parameter	This Product	L99LD21Q6TR	TPS92692-Q1	LT3966
Package	QFN40L 6x6	QFN40L 6x6	HTSSOP-20	QFN-40
Brand	STMicroelectronics	STMicroelectronics	Texas Instruments	Analog Devices
Number of Outputs	2	2	1	2
Output Current per Channel	1.5 A	1.5 A	5 A	1 A
Input Voltage Range	5.5 V to 24 V	5.5 V to 24 V	4.5 V to 65 V	4 V to 36 V
Topology	Boost	Boost	Boost	Boost
Dimming	PWM	PWM	PWM	PWM
AEC-Q100 Qualified	Yes	Yes	Yes	No

Key Differentiators

Two independent channels with high current capability (vs TPS92692-Q1)
AEC-Q100 qualified for automotive reliability (vs LT3966)
Integrated boost controller and high-side current source (vs TPS92692-Q1)

Design Notes

The L99LD21 in a QFN40L package requires proper thermal management. Ensure adequate copper area on the PCB and consider thermal vias to dissipate heat from the exposed pad. For high-current applications, calculate the power dissipation and verify the junction temperature stays within limits.

Place the boost converter components, including the inductor and output capacitor, close to the IC to minimize parasitic inductance. Use a solid ground plane and separate the power ground from the analog ground to reduce noise. Follow the layout guidelines in the datasheet for optimal performance.

Ensure the SPI communication lines are properly terminated and have appropriate pull-up resistors. The fault output should be monitored by the microcontroller to implement diagnostic functions. Verify the PWM dimming frequency and duty cycle to avoid audible noise in the LED driver.