LT3922-1

36V, 2.3A Synchronous Step-Up LED Driver with 25,000:1 PWM Dimming

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Overview

Features and Benefits
Product Details

Features and Benefits

±2.5% LED Current Regulation
±2% Output Voltage Regulation
25,000:1 PWM Dimming at 100Hz
128:1 Internal PWM Dimming
Spread Spectrum Frequency Modulation
Silent Switcher^® Architecture for Low EMI
Operates in Boost, Buck Mode and Buck-Boost Mode

2.8V to 36V Input Voltage Range
Up to 34V LED String Voltage
2.3A, 40V Internal Switches
200kHz to 2MHz Switching Frequency with SYNC
Analog or Duty Cycle LED Current Control
Open/Short LED Protection and Fault Indication
Thermally Enhanced 28-Lead (4mm × 5mm) QFN
AEC-Q100 Qualified for Automotive Applications

Product Details

The LT3922-1 is a monolithic, synchronous, step-up DC/ DC converter that utilizes fixed-frequency, peak current control and provides PWM dimming for a string of LEDs. The LED current is programmed by an analog voltage or the duty cycle of pulses at the CTRL pin. The LT3922-1 will maintain ±2.5% current regulation through an external sense resistor over a wide range of output voltages.

The switching frequency is programmable from 200kHz to 2MHz by an external resistor at the RT pin or by an external clock applied at the SYNC/SPRD pin. With the optional spread spectrum frequency modulation enabled, the frequency varies from 100% to 125% to reduce EMI. The LT3922-1 also includes a driver for an external high side PMOS for PWM dimming and an internal PWM signal generator for analog control of PWM dimming. When an external signal is available, the LT3922-1 can perform 25,000:1 PWM dimming with 100Hz PWM pulses.

Additional features include an accurate external reference voltage for use with the CTRL and PWM pins, an LED current monitor, an accurate EN/UVLO pin threshold, open-drain fault reporting for open-circuit and short-circuit load conditions, and thermal shutdown.

APPLICATIONS

Automotive and Industrial Lighting
Machine Vision

Product Categories

Power Management

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Product Lifecycle Production

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Evaluation Kits (1)

DC2857A

36V 2A Boost LED Driver with 25,000:1 PWM Dimming

DC2857A

View Detailed Evaluation Kit Information

Demonstration circuit DC2857A is a 36V 2A synchronous 2MHz boost LED driver featuring the LT3922-1. It drives a single string of LEDs at 330mA up to 34V when V_IN is between 7V and 28V. It runs down to 4V_IN with reduced I_LED and can withstand V_IN as high as 36V, but has overvoltage lockout (OVLO) set for 28V for this application. DC2857A runs at 2MHz switching frequency. Spread spectrum frequency modulation (SSFM) can be turned on with a simple jumper, reducing EMI. DC2857A comes with low EMI features including optimized layout, SSFM and input EMI filter. It passes CISPR 25 class 5 conducted and radiated EMI. It is protected against both open and short LED conditions and reports the faults.

The LT3922-1 has an input voltage range from 2.8V to 36V. Its internal synchronous 2A 40V switches allow up to 34V of LEDs on the output with room for over voltage protection and overshoot during an open LED event. It has adjustable switching frequency between 200kHz and 2.5MHz. It can be synchronized to an external source or programmed with SSFM for low EMI. The PWMTG highside PWM MOSFET driver assists with short-circuit protection and versatility. LT3922-1 can be configured as a boost, boost-buck, or buck mode LED driver and maintain all of its low EMI, PWM dimming, and fault diagnostic features.

The LT3922-1 can be PWM dimmed with an external PWM signal or an internally-generated PWM signal. DC2857A has a jumper that can be set to switch between internallygenerated PWM signal, externally-generated PWM signal, and no PWM signal (100% on). It can be analog dimmed with a control voltage on its control pin (CTRL). When run with both PWM dimming and spread spectrum, the spread spectrum aligns itself with the PWM signal for flicker-free operation.

Small ceramic input and output capacitors are used to save space and cost. The board is designed with tiny, high frequency capacitors on both sides of the VOUT pins for a reduction in radiated EMI. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 37.5V if the LED string is opened, although it may reach almost 40V peak during transient from running LEDs to open. There is a protection diode from LED+ to GND to prevent negative ringing during a short-circuit. The output current can be monitored through the ISMON output pin.

Undervoltage and overvoltage lockout can be adjusted on the circuit with a few simple resistor choices.

There is an EMI filter on the input of DC2857A. Please follow the recommend layout and four-layer thickness of DC2857A for low EMI applications.

The LT3922-1 data sheet gives a complete description of the part, operation and applications information. The LT3922EUFD-1 is assembled in a 28-lead plastic 4mm × 5mm QFN package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the data sheet section Layout Considerations.

Resources

Documentation & Resources

Data Sheets

LT3922-1: 36V, 2.3A Synchronous Step-Up LED Driver with 25,000:1 PWM Dimming Data Sheet (Rev. A)
2/8/2021
PDF

Reliability Data

R580 Reliability Data
4/17/2019
PDF

User Guides

DC2857A - Demo Manual (Rev. 0)
9/11/2018
PDF

Rarely Asked Questions

Mitigation Strategies for Tricky FM Band Conducted EMI
4/9/2021

Technical Articles

Automotive LED Driver Power Conversion Topology Guide
6/1/2022 Analog Dialogue
Does the Assembly Orientation of an SMPS Inductor Affect Emissions?
6/4/2021 Analog Dialogue

Tools & Simulations

LTspice

LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

LTspice downloads and documentation

Models for the following parts are available in LTspice:

LT3922

LT3922-1

Design Resources

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.

Part Number	Material Declaration	Reliability Data	Pin/Package Drawing	CAD Symbols, Footprints & 3D Models
LT3922EUFD-1#PBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922EUFD-1#TRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922EUFD-1#WPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922EUFD-1#WTRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922HUFD-1#PBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922HUFD-1#TRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922HUFD-1#WPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922HUFD-1#WTRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922IUFD-1#PBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922IUFD-1#TRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922IUFD-1#WPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
LT3922IUFD-1#WTRPBF	Material Declaration	Reliability Data	28-Lead QFN (4mm x 5mm x 0.75mm w/ EP)	Ultra Librarian SamacSys
Wafer Fabrication Data		R580 Reliability Data

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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.