Analog Devices LT8391 | Demoboard DC2345A

Description

Demonstration circuit 2345A is a 60V synchronous4-switch buck-boost LED controller with spread spectrumfeaturing the LT®8391 LED driver. It accepts an input voltagefrom 4V to 60V and drives a single string of LEDs up to25V at 2A. DC2345A runs at 400kHz switching frequencywithout spread spectrum, but spread spectrum frequencymodulation (SSFM) can be enabled with a simple jumper.SSFM spreads the switching frequency to fsw ±15% forreduced EMI.The LT8391 has a wide input voltage range down to 4V andup to 60V. It has adjustable switching frequency between150kHz and 600kHz. There is a simple jumper option forexternal frequency synchronization, spread spectrumfrequency modulation, or neither.The LT8391 can be PWM dimmed with an external PWMsignal and an internally-generated PWM signal. DC2345Ahas a jumper that can e set to switch between internallygeneratedPWM signal, externally-generated PWM signal,and no PWM signal (100% on). It can be analog dimmedwith a control voltage on either of its two control pins.LT8391 features both open LED and short LED (LED+ toGND) protection as well as a fault output flag.When run with both PWM dimming and spread spectrum,the spread spectrum aligns itself with the PWM signal forflicker-free operation.Small ceramic input and output capacitors are used to savespace and cost. The board is designed with capacitors onL, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of LinearTechnology Corporation. All other trademarks are the property of their respective owners.both sides of the synchronous switches for a reductionin radiated EMI. The open LED overvoltage protectionuses the IC’s constant voltage regulation loop to regulatethe output to approximately 29.7V if the LED string isopened although it may reach 32V peak during transientfrom running LEDs to open. There is a protection diodefrom LED+ to GND to prevent negative ringing during ashort-circuit with long wires.Undervoltage lockout can be adjusted on the circuit witha few simple resistor choices.There is an EMI filter on the input of DC2345A. This filterhas a 3.2µH inductor and two 4.7µF capacitors. It is effectivein reducing the conducted EMI in the AM band topass CISPR25 class 5 regulations. When run with SSFM,DC2345A has low conducted EMI.The LT8391 data sheet gives a complete description ofthe part, operation and applications information. The datasheet must be read in conjunction with this Demo Manualfor demonstration circuit DC2345A. The LT8391EFE isassembled in a 28-lead plastic TSSOP (FE) package witha thermally enhanced ground pad. Proper board layoutis essential for maximum thermal performance. See thedata sheet section ‘Layout Considerations’.

Features

n 4-Switch Single Inductor Architecture Allows VINAbove, Below or Equal to VOUTn Synchronous Switching: Up to 98% Efficiencyn Proprietary Peak-Buck Peak-Boost Current Moden Wide VIN Range: 4V to 60Vn Wide VOUT Range: 0V to 60V (51V LED)n ±3% LED Current Accuracyn 2000:1 External and 128:1 Internal PWM Dimmingn High Side PMOS PWM Switch Drivern Integrated Bootstrap Diodesn No Top MOSFET Refresh Noise in Buck or Boostn Adjustable and Synchronizable: 150kHz to 650kHzn Flicker-Free Spread Spectrum for Low EMIn Open and Short LED Protection with Fault Reportingn Available in 28-Lead TSSOP with Exposed Pad and28-Lead QFN (4mm × 5mm)

Typical applications

• High Power LED Lighting
• Automotive Head Lamps/Running Lamps

More information

• Datasheet
• IC product information