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General Description

The MAX16818 pulse-width modulation (PWM) LED

driver controller provides high-output-current capability

in a compact package with a minimum number of exter-

nal components. The MAX16818 is suitable for use in

synchronous and nonsynchronous step-down (buck)

topologies, as well as in boost, buck-boost, SEPIC, and

Cuk LED drivers. The MAX16818 is the first LED driver

controller that enables Maxim’s technology for fast LED

current transients of up to 20A/µs and 30kHz dimming

frequency.

This device utilizes average-current-mode control that

enables optimal use of MOSFETs with optimal charge

and on-resistance characteristics. This results in the

minimized need for external heatsinking even when deliv-

ering up to 30A of LED current. True differential sensing

enables accurate control of the LED current. A wide dim-

ming range is easily implemented to accommodate an

external PWM signal. An internal regulator enables oper-

ation over a wide input voltage range: 4.75V to 5.5V or 7V

to 28V and above with a simple external biasing device.

The wide switching frequency range, up to 1.5MHz,

allows for the use of small inductors and capacitors.

The MAX16818 features a clock output with 180° phase

delay to control a second out-of-phase LED driver to

reduce input and output filter capacitors size or to mini-

mize ripple currents. The MAX16818 offers programma-

ble hiccup, overvoltage, and overtemperature protection.

The MAX16818ETI+ is rated for the extended tempera-

ture range (-40°C to +85°C) and the MAX16818ATI+ is

rated for the automotive temperature range (-40°C to

+125°C). This LED driver controller is available in a lead-

free, 0.8mm high, 5mm x 5mm 28-pin TQFN package with

exposed paddle.

Applications

● Front Projectors/Rear Projection TVs

● Portable and Pocket Projectors

● LCD TVs and Display Backlight

Features

● High-Current LED Driver Controller IC, Up to 30A

Output Current

● Average-Current-Mode Control

● True-Differential Remote-Sense Input

● 4.75V to 5.5V or 7V to 28V Input Voltage Range

● Programmable Switching Frequency or External

Synchronization from 125kHz to 1.5MHz

● Clock Output for 180° Out-of-Phase Operation

● Integrated 4A Gate Drivers

● Output Overvoltage and Hiccup Mode Overcurrent

Protection

● Thermal Shutdown

● Thermally Enhanced 28-Pin Thin QFN Package

● -40°C to +125°C Operating Temperature Range

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

Pin Configuration appears at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

MAX16818ATI+ -40°C to +125°C 28 TQFN-EP*

MAX16818ETI+ -40°C to +85°C 28 TQFN-EP*

HIGH-FREQUENCY

PULSE TRAIN

LED

7V TO 28V

CSP

NOTE: MAXIM TOPOLOGY

PGND

ILIM

OVI

CLP

MAX16818

MAX16818 1.5MHz, 30A High-Efficiency, LED Driver

with Rapid LED Current Pulsing

19-0666; Rev 3; 4/14

Simplied Diagram

Ordering Information

EVALUATION KIT AVAILABLE

Summary of content (25 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing General Description The MAX16818 pulse-width modulation (PWM) LED driver controller provides high-output-current capability in a compact package with a minimum number of external components. The MAX16818 is suitable for use in synchronous and nonsynchronous step-down (buck) topologies, as well as in boost, buck-boost, SEPIC, and Cuk LED drivers.
PAGE 2
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Absolute Maximum Ratings IN to SGND............................................................-0.3V to +30V BST to SGND.........................................................-0.3V to +35V BST to LX.................................................................-0.3V to +6V DH to LX..................................... -0.3V to [(VBST - VLX_) + 0.3V] DL to PGND.............................................. -0.
PAGE 3
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Electrical Characteristics (continued) (VCC = 5V, VDD = VCC, TA = TJ = TMIN to TMAX, unless otherwise noted. Typical specifications are at TA = +25°C.
PAGE 4
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Electrical Characteristics (continued) (VCC = 5V, VDD = VCC, TA = TJ = TMIN to TMAX, unless otherwise noted. Typical specifications are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN Maximum Load Capacitance TYP MAX UNITS 50 V_IOUT Output to IOUT Transfer Function RSENSE = 1mW, 100mV ≤ V_IOUT ≤ 5.5V 132.3 Offset Voltage pF 135 137.
PAGE 5
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Operating Characteristics (TA = +25°C, using Figure 5, unless otherwise noted.) VIN = 12V 30 20 VIN = 5V 10 500 700 900 1100 1300 1500 tF (ns) MAX16818 toc03 MAX16818 toc02 35 26.0 85 60 VIN = 12V fSW = 250kHz 0 1 2 3 4 DRIVER RISE TIME vs. DRIVER LOAD CAPACITANCE 5.25 5.15 VCC (V) 4 100 VIN = 24V 5.05 4.95 12 16 20 4.75 60 DL 40 VIN = 5V 4.
PAGE 6
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Operating Characteristics (continued) (TA = +25°C, using Figure 5, unless otherwise noted.
PAGE 7
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Pin Description PIN NAME 1 PGND FUNCTION 2, 7 N.C. 3 DL 4 BST 5 LX Source connection for the high-side MOSFET. 6 DH High-Side Gate Driver Output. Drives the gate of the high-side MOSFET. 8, 22, 25 SGND 9 CLKOUT Oscillator Output. Rising edge of CLKOUT is phase-shifted from the rising edge of DH by 180°. 10 PGOOD Power-Good Output 11 EN Output Enable.
PAGE 8
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Pin Description (continued) PIN NAME FUNCTION 21 CSP Current-Sense Differential Amplifier Positive Input. The differential voltage between CSN and CSP is amplified internally by the current-sense amplifier (gain = 34.5) to measure the inductor current. 23 SENSE- Differential LED Current-Sensing Negative Input. SENSE- is used to sense the LED current.
PAGE 9
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Application Circuits ON/OFF R6 C3 VLED R3 R4 R5 VIN 7V TO 28V VCC C2 14 C10 C9 R12 LIM 13 12 V_IOUT RT/SYNC 9 10 PGOOD CLKOUT 11 EN L1 8 SGND 15 OVI N.C. 7 16 CLP DH 6 17 EAOUT LX 5 VLED D1 Q1 R11 C8 C7 R10 18 EAN BST 4 MAX16818 19 DIFF DL 3 20 CSN N.C.
PAGE 10
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Application Circuits (continued) ON/OFF R6 C3 VLED R3 R4 R5 VIN 7V TO 28V VCC LED STRING 1 TO 6 LEDS R2 C2 14 C10 C9 R12 LIM 13 12 V_IOUT RT/SYNC 9 10 11 EN L1 8 SGND PGOOD CLKOUT 15 OVI N.C. 7 16 CLP DH 6 17 EAOUT LX 5 D1 VLED Q1 VCC R11 C8 C7 R10 18 EAN BST 4 MAX16818 MAX4073T R7 RS- OUT C1 19 DIFF DL 3 20 CSN N.C.
PAGE 11
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Application Circuits (continued) ON/OFF R6 C4 VLED R3 R4 R5 VIN 7V TO 28V VCC C3 14 C11 C10 R12 LIM 13 12 11 V_IOUT RT/SYNC 9 10 EN L1 8 PGOOD CLKOUT 15 OVI SGND N.C. 7 16 CLP DH 6 17 EAOUT LX 5 C1 VLED D1 Q1 R11 C9 C8 R10 18 EAN C2 LED STRING BST 4 MAX16818 19 DIFF DL 3 20 CSN N.C.
PAGE 12
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Application Circuits (continued) ON/OFF C3 VLED R3 R4 R5 14 C11 C10 R12 R6 13 12 VCC VIN 7V TO 18V 9 10 15 OVI 8 SGND N.C. 7 16 CLP DH 6 17 EAOUT LX 5 LIM V_IOUT RT/SYNC 11 EN PGOOD CLKOUT C2 Q1 R11 C9 C8 R10 18 EAN MAX16818 BST 4 L1 C4 R7 DL 3 20 CSN N.C.
PAGE 13
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Typical Application Circuits (continued) VCC R4 14 LIM C11 C10 R10 R3 C3 13 12 VIN 7V TO 28V ON/OFF V_IOUT RT/SYNC 9 10 PGOOD CLKOUT 11 EN 8 SGND 15 OVI N.C. 7 16 CLP DH 6 17 EAOUT LX 5 C2 R9 C9 C8 R8 18 EAN BST 4 MAX16818 L1 C4 R5 Q1 D1 19 DIFF DL 3 20 CSN N.C.
PAGE 14
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Functional Diagram VCC IS EN 0.5V x VCC 5V LDO REGULATOR IN VCC UVLO POR TEMP SENSOR TO INTERNAL CIRCUITS LIM HICCUP MODE CURRENT LIMIT MAX16818 126.7kΩ VCM 100kΩ 0.5 x VCLAMP CLP CA CSN CLK OSCILLATOR CLKOUT RT VDD PWM COMPARATOR RAMP CPWM BST S Q DH LX 2 x fS (V/s) R Q DL RAMP GENERATOR DIFF PGND +0.
PAGE 15
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Detailed Description The MAX16818 is a high-performance average-current-mode PWM controller for high-power, high-brightness LEDs (HB LEDs). Average current-mode control is the ideal method for driving HB LEDs. This technique offers inherently stable operation, reduces component derating and size by accurately controlling the inductor current.
PAGE 16
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing The oscillator also generates a 2VP-P voltage-ramp signal for the PWM comparator and a 180? out-of-phase clock signal for CLKOUT to drive a second LED regulator out-of-phase. Synchronization The MAX16818 can be easily synchronized by connecting an external clock to RT/SYNC. If an external clock is present, then the internal oscillator is disabled and the external clock is used to run the device.
PAGE 17
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Inductor Current-Sense Amplifier The differential current-sense amplifier (CA) provides a DC gain of 34.5. The maximum input offset voltage of the current-sense amplifier is 1mV and the common-mode voltage range is 0 to 5.5V (IN = 7V to 28V). The current-sense amplifier senses the voltage across a current-sense resistor. The maximum common-mode voltage is 3.6V when VIN = 5V.
PAGE 18
MAX16818 Differential Amplifier The DIFF AMP facilitates remote sensing at the load (Figure 7). It provides true differential LED current (through the RLS sense resistor) sensing while rejecting the common-mode voltage errors due to high-current ground paths. The VEA provides the difference between the differential amplifier output (DIFF) and the desired LED current-sense voltage. The differential amplifier has a bandwidth of 3MHz. The difference between SENSE+ and SENSE- is regulated to 0.6V.
PAGE 19
MAX16818 Applications Information Application Circuit Descriptions This section provides some detail regarding the application circuits in the Simplified Diagram and Figures 1–5. The discussion includes some description of the topology as well as basic attributes. High-Frequency LED Current Pulser 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing span from the output to the input.
PAGE 20
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing nous MOSFET keeps the power dissipation to a minimum, especially when the input voltage is large when compared to the voltage on the LED string. It is important to keep the current-sense resistor, R1, inside the LC loop, so that ripple current is available. To regulate the LED current, R2 creates a voltage that the differential amplifier compares to 0.6V.
PAGE 21
MAX16818 1.
PAGE 22
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Current Limit Buck: I x D(1 − D) CIN = OUT ∆VQ x fSW where IOUT is the output current of the converter. For example, at VIN = 13.2V, VLED = 7.8V, IOUT = 1A, ∆IL = 0.4A, and fSW = 330kHz, the ESR and input capacitance are calculated for the input peak-to-peak ripple of 100mV or less yielding an ESR and capacitance value of 25mΩ and 10µF.
PAGE 23
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Compensation The main control loop consists of an inner current loop (inductor current) and an outer LED current loop. The MAX16818 uses an average current-mode control scheme to regulate the LED current (Figure 7). The VEA output provides the controlling voltage for the current source. The inner current loop absorbs the inductor pole reducing the order of the LED current loop to that of a single-pole system.
PAGE 24
Keep the SGND and PGND isolated and connect them at one single point. 6) Run the current-sense lines CSP and CSN very close to each other to minimize the loop area. Similarly, run the remote voltage-sense lines SENSE+ and SENSE- close to each other. Do not cross these critical signal lines through power circuitry. Sense the current right at the pads of the current-sense resistors. 7) Avoid long traces between the VDD bypass capacitors, the driver output of the MAX16818, the MOSFET gates, and PGND.
PAGE 25
MAX16818 1.5MHz, 30A High-Efficiency, LED Driver with Rapid LED Current Pulsing Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 10/06 Initial release 1 6/08 Replaced Compensation section and corrected Figure 4. 2 3/09 Updated formula in Inductor Selection section.