Maxim’s MAX16834 is a current-mode high-brightness LED (HB LED) that can be used in boost, boost-buck, SEPIC, and high-side buck topologies. In addition to driving N-channel power MOSFETs for switching control, it can also drive N-channel PWM dimming switches. The input operating voltage is 4.75V to 28V, the operating frequency is 100kHz-1MHz, and 3000:1 PWM dimming/analog dimming. In single-string LED LCD backlight, automotive front and rear lighting, projection system RGB LED light source, DC/DC boost / boost-buck converter and MR16, M111 lighting. This article describes the MAX16834 main features, block diagram, various application circuits, and reference design features, Circuit diagram, and PCB layout for a 112W long-string LED boost driver with all-ceramic capacitors.
The MAX16834 is a current-mode high-brightness LED (HB LED) driver for boost, boost-buck, SEPIC, and highside buck topologies. In addition to driving an n-channel power MOSFET switch controlled by the switching controller, it also drives an n-channel PWM dimming switch to achieve LED PWM dimming. The MAX16834 integrates all the building blocks necessary to implement a fixed-frequency HB LED driver with wide-range dimming control.
The MAX16834 features constant-frequency peak current-mode control with programmable slope compensation to control the duty cycle of the PWM controller. A dimming driver designed to drive an external n-channel MOSFET in series with the LED string provides wide-range dimming control up to 20kHz. In addition to PWM dimming, the MAX16834 provides analog dimming using a DC input at REFI. The programmable switching frequency (100kHz to 1MHz) allows design optimization for efficiency and board space reduction.
A single resistor from RT/SYNC to ground sets the switching frequency from 100kHz to 1MHz while an external clock signal at RT/SYNC disables the internal oscillator and allows the MAX16834 to synchronize to an external clock. The MAX16834’s integrated highside current-sense amplifier eliminates the need for a separate high-side LED current-sense amplifier in boost-buck applications.
The MAX16834 operates over a wide supply range of 4.75V to 28V and includes a 3A sink/source gate driver for driving a power MOSFET in high-power LED driver applications. It can also operate at input voltages greater than 28V in boost configuration with an external voltage clamp. The MAX16834 is also suitable for DC/DC converter applications such as boost or boostbuck.
Additional features include external enable/disable input, an on-chip oscillator, fault indicator output (FLT) for LED open/short or overtemperature conditions, and an overvoltage protection sense input (OVP+) for true overvoltage protection.
The MAX16834 is available in a thermally enhanced 4mm x 4mm, 20-pin TQFN-EP package and in a thermally enhanced 20-pin TSSOP-EP package and is specified over the automotive -40℃ to +125℃ temperature range.
MAX16834 main features:
_ Wide Input Operating Voltage Range (4.75V to 28V)
_ Works for Input Voltage > 28V with External Voltage Clamp on VIN for Boost Converter
_ 3000:1 PWM Dimming/Analog Dimming
_ Integrated PWM Dimming MOSFET Driver
_ Integrated High-Side Current-Sense Amplifier for LED Current Sense in Boost-Buck Converter
_ 100kHz to 1MHz Programmable High-Frequency Operation
_ External Clock Synchronization Input
_ Programmable UVLO
_ Internal 7V Low-Dropout Regulator
_ Fault Output (FLT) for Overvoltage, Overcurrent, and Thermal Warning Faults
_ Programmable True Differential Overvoltage Protection
_ 20-Pin TQFN-EP and TSSOP-EP Packages
Single-String LED LCD Backlighting
Automotive Rear and Front Lighting
Projection System RGB LED Light Sources
Architectural and Decorative Lighting (MR16, M111)
Spot and Ambient Lights
DC-DC Boost/Boost-Buck Converters
Figure 1. Block Diagram of the MAX16834
Boost LED Driver
Figure 2. MAX16834 boost-buck LED driver circuit (VLED+ < 28V)
Figure 3. MAX16834 boost LED driver circuit with automotive load-dump protection
Figure 4. MAX16834 high-side step-down LED driver circuit
Figure 5. MAX16834 boost DC/DC converter circuit
Figure 6. MAX16834 boost-buck DC/DC converter circuit
112W Long String LED Boost Driver Reference Design Using All Ceramic Capacitors
This reference design uses the MAX16834 to create a high-powered LED driver for a very long string(s) of LEDs. The LED current is adjustable with a potentiometer, and can be set as high as 1.5A into as many as 20 LEDs ( 75V total). For long life, ceramic capacitors are used for both input and output decoupling.
This is a reference design for a 112.5W boost LED driver that uses the MAX16834 for long strings of LEDs. These long LED strings are commonly found in streetlights and parking garage lights.
112W Long String LED Boost Driver Reference Design Key Specifications:
Input voltage: 24VDC ±5% (at 1.49A)
VLED configuration: Two parallel strings. Each string consists of 19 WLEDs and a 5Ω resistor for current balancing. Current is 750mA per sting for a total of 1.5A into 75V.
Dimming: 50μs (min) on-pulse for up to a 200:1 dimming ratio with a 100Hz dimming frequency
Reference Design Key Features:
♦ 7V to 28V Wide Supply Voltage Range
♦ Configured for Boost Operation
♦ Configurable for Buck-Boost Operation
♦ 1A Output Current
♦ Analog Linear Dimming Control
♦ PWM Dimming Control
♦ Open/Short-Circuit LED Fault Indicator (FLT)
♦ Demonstrates Output Overvoltage Protection
♦ Optional Load Dump Circuit
♦ Fully Assembled and Tested
Figure 6. 112W Long String LED Boost Driver Reference Design Outline Drawing
Figure 7. 112W Long String LED Boost Driver Reference Design Circuit Diagram
112W Long String LED Boost Driver Reference Design Bill of Materials:
Figure 8. 112W Long String LED Boost Driver Reference Design PCB Component Layout
For details, see: