Features and Benefits
- 3000:1 External PWM Dimming
- 250:1 Internal PWM Dimming
- Wide VIN Operating Range: 2.5V to 38.5V
- Synchronous Boost Output Voltage up to 60V
- Spread-Spectrum Frequency Modulation for Lower EMI
- PMOS Switch Driver for PWM and Output Disconnect
- Constant Current (±3.5%) Regulation
- Constant Voltage (±2%) Regulation
- Rail-to-Rail LED Current Sense: 0V to 60V
- Programmable VIN Undervoltage Lockout
- Analog Dimming via Two Control Pins
- 100kHz to 1MHz Operation
- Programmable Open LED Protection with OPENLED Flag
- Short-Circuit Protection and SHORTLED Flag
- Drives LEDs in Boost, SEPIC, Buck Mode, or BuckBoost Mode Configurations
- 28 Lead TSSOP and QFN (4mm × 5mm) Exposed Pad Packages
The LT3762 is a synchronous DC/DC controller designed to operate as a constant-current source and constant-voltage regulator. It features a programmable internal PWM dimming signal generator and a synchronous gate driver. The LT3762 is ideally suited for driving high current LEDs with high efficiency and reduced power loss. Rail-to-rail switch current sensing enables synchronous boost topologies and nonsynchronous topologies such as SEPIC. A voltage feedback pin serves as the input for several LED protection features and also allows the converter to operate as a constant-voltage source.
A frequency adjust pin allows the user to program the frequency from 100kHz to 1MHz to optimize efficiency, performance and external component size. Adding a capacitor at SSFM pin activates the Spread-Spectrum Modulation feature to reduce EMI. The LT3762 also includes an integrated DC/DC converter to efficiently produce a regulated 7.5V supply for the N-channel MOSFET gate drivers. The PWM pin controls PWMTG to drive the P-channel MOSFET, allowing a high PWM dimming range (3000:1) and providing LED overcurrent protection and short-circuit protected boost capability.
- Industrial and Automotive Lighting
- Accurate Current-Limited Voltage Regulators
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)
Demonstration circuit DC2342A is a 60V synchronous boost LED controller featuring the LT®3762. It drives a single string of LEDs at 2A up to 32V when VIN is between 7V and 28V. It runs down to 4VIN with reduced ILED and can withstand VIN transients as high as 30V. DC2342A runs at approximately 300kHz switching frequency. Spread spectrum frequency modulation (SSFM) can be turned on with a simple jumper, reducing EMI. DC2342A is designed for high power step-up LED controller applications that require excellent efficiency across the VIN range. This demonstration circuit is protected against both open and short LED conditions, each having its own flag.
The LT3762 has an input range from 2.5V to 42V. It has an adjustable switching frequency between 100kHz and 1MHz. Enabling SSFM spreads the switching frequency from fSW down to fSW – 30% for reduced EMI. SSFM speed is set by placing a capacitor from the SSFM pin of the LT3762 to ground, and can be disabled by shorting this pin to GND. DC2342A has a simple jumper option to enable/disable spread spectrum frequency modulation.
The LT3762 can be PWM dimmed with an external PWM signal, as well as an internally generated PWM signal. A capacitor from PWM to GND of the LT3762 sets the PWM frequency, while the PWM duty cycle is determined by the voltage on the DIM terminal. Between 0V and 3V, VDIM gives between 0.4% and 97% PWM duty cycle. DC2342A has a jumper that can be set to switch between internally generated PWM signal, externally generated PWM signal, and no PWM signal (100% on). When run with both PWM dimming and spread spectrum enabled, the spread spectrum aligns itself with the PWM signal for flicker free operation. DC2342A can also be analog dimmed by placing a voltage source at either of its two CTRL turrets.
Small ceramic input and output capacitors are used to save space and cost. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 35.5V if the LED string is opened, although it may reach almost 40V peak during the transient caused by an open circuit. There is a protection diode from LED+ to GND to prevent negative ringing during a short-circuit.
Undervoltage lockout can be adjusted on the circuit with a few simple resistor choices. Further modifications can be made to DC2342A to reconfigure the circuit from a boost topology to operate as a buck-mode or buck-boost mode LED driver. Please consult the factory for details.
The LT3762 data sheet gives a complete description of the part, operation and applications information. The data sheet must be read in conjunction with this Demo Manual for demonstration circuit DC2342A. The LT3762EUFD 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.
Documentation & Resources
Synchronous Boost Converter Powers High Current LEDs Even at Low Input Voltages2/1/2019 Analog Dialogue
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