Datasheet

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General Description

The MAX16812 is a peak-current-mode LED driver with

an integrated 0.2Ω power MOSFET designed to control

the current in a single string of high-brightness LEDs

(HB LEDs). The MAX16812 can be used in multiple

converter topologies such as buck, boost, or buck-boost.

The MAX16812 operates over a 5.5V to 76V wide supply

voltage range.

The MAX16812 features a low-frequency, wide-range

brightness adjustment (100:1), analog and PWM dim-

ming control input, as well as a resistor-programmable

EMI suppression circuitry to control the rise and fall times

of the internal switching MOSFET. A high-side LED cur-

rent-sense amplifier and a dimming MOSFET driver are

also included, simplifying the design and reducing the

total component count.

The MAX16812 uses peak-current-mode control, adjust-

able slope compensation that allows for additional design

flexibility. The device has two current regulation loops.

The first loop controls the internal switching MOSFET

peak current, while the second current regulation loop

controls the LED current. Switching frequency can be

adjusted from 125kHz to 500kHz.

Additional features include adjustable UVLO, soft-start,

external enable/disable input, thermal shutdown, a 1.238V

1% accurate buffered reference, and an on-chip oscillator.

An internal 5.2V linear regulator supplies up to 20mA to

power external devices.

The MAX16812 is available in a thermally enhanced 5mm

x 5mm, 28-pin TQFN-EP package and is specified over

the automotive -40°C to +125°C temperature range.

Applications

● Architectural and Industrial Lighting

Features

● Integrated 76V, 0.2Ω (typ) Power MOSFET

● 5.5V to 76V Wide Input Range

● Adjustable LED Current with 5% Accuracy

● Floating Differential LED Current-Sense Amplifier

● Floating Dimming N-Channel MOSFET Driver

● PWM LED Dimming with:

• PWM Control Signal

• Analog Control Signal

• Chopped V

Input

● Peak-Current-Mode Control

● 125kHz to 500kHz Adjustable Switching Frequency

● Adjustable UVLO and Soft-Start

● Output Overvoltage Protection

● 5µs LED Current Rise/Fall Times During Dimming

Minimize EMI

● Overtemperature and Short-Circuit Protection

19-0880; Rev 1; 4/14

Typical Application Circuit and Pin Configuration appear

at end of data sheet.

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

*EP = Exposed pad.

PART TEMP RANGE PIN-PACKAGE

MAX16812ATI+ -40°C to +125°C 28 TQFN-EP*

TGRM

H_REG

OV1

OV2

TGRM

DIM

TGRM

VOUT

L_REG

DOUT

VOUT

SRC

DRV

SLP

COMP

COMP1

BUCK-BOOST CONFIGURATION

COMP1

SLP

SRC

OUT

COMP2

CS-

CS+

DGT

H_REG

SGND

AGND

REFI

REF

CS_OUT

MAX16812

MAX16812 Integrated High-Voltage LED Driver

with Analog and PWM Dimming Control

Simplied Diagram

Ordering Information

EVALUATION KIT AVAILABLE

Summary of content (20 pages)

PAGE 1
EVALUATION KIT AVAILABLE Integrated High-Voltage LED Driver with Analog and PWM Dimming Control ●● Adjustable LED Current with 5% Accuracy ●● Floating Differential LED Current-Sense Amplifier ●● Floating Dimming N-Channel MOSFET Driver ●● PWM LED Dimming with: • PWM Control Signal • Analog Control Signal • Chopped VIN Input ●● Peak-Current-Mode Control ●● 125kHz to 500kHz Adjustable Switching Frequency ●● Adjustable UVLO and Soft-Start ●● Output Overvoltage Protection ●● 5µs LED Current Rise/Fall Times Du
PAGE 2
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Absolute Maximum Ratings (All voltages are referenced to AGND, unless otherwise noted.) SGND....................................................................-0.3V to +0.3V IN, EN, LX, DIM......................................................-0.3V to +80V L_REG, GT, DRV.....................................................-0.3V to +6V RT, REF, REFI, CS_OUT, FB, COMP, SRC, SLP, TGRM, OV........................................
PAGE 3
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Electrical Characteristics (continued) (VIN = VEN = 12V, CL_REG = 3.3µF, CH_REG = 1µF, CREF = 47nF, VTGRM = 0V, RSRC = 0.2Ω, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS PWM COMPARATOR ILKCOMP VCOMP = 1V, VSRC = 0.5V, VTGRM = 1V, VDIM = 0.5V -0.10 +0.10 µA SRC Input Leakage Current ILKSRC VCOMP = 0V, VSRC = 0.
PAGE 4
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Electrical Characteristics (continued) (VIN = VEN = 12V, CL_REG = 3.3µF, CH_REG = 1µF, CREF = 47nF, VTGRM = 0V, RSRC = 0.2Ω, RCS = 1Ω, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS HIGH-SIDE DIMMING LINEAR REGULATOR ((VHV - VLV) = 21V) Minimum Output Current IDGT VLV = VCS-, (VCS+ - VCS-) = 0.
PAGE 5
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Typical Operating Characteristics (VIN = VEN = 12V, CL_REG = 3.3µF, CH_REG = 1µF, VTGRM = 0V, TA = +25°C, unless otherwise noted.) RDS(ON) (Ω) 3.250 0.20 TA = +25C 1.0 0.8 0.6 TA = -40C 0.10 1.2 0.4 0.05 0.2 0 0 1.5 2.0 2.5 3.0 3.150 3.100 3.050 3.000 2.2 2.8 3.4 4.0 4.6 5.2 5.8 6.4 2.900 7.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 VGT (V) TEMPERATURE (°C) SHUTDOWN CURRENT vs.
PAGE 6
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Typical Operating Characteristics (continued) (VIN = VEN = 12V, CL_REG = 3.3µF, CH_REG = 1µF, VTGRM = 0V, TA = +25°C, unless otherwise noted.) 5.4 5.3 5.2 1.30 5.1 VL_REG (V) 1.35 1.25 1.20 4.9 4.8 1.10 4.7 1.05 4.6 4.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 TA = -40C VIN = 7.5V 0 2 4 6 8 10 12 14 16 18 20 RT = 50kΩ 100 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 300 200 4.2 4.1 100 4.0 3.9 3.8 3.7 3.
PAGE 7
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Pin Description PIN NAME 1 FB FUNCTION 2 COMP 3 REFI Reference Input. VREFI provides the reference voltage for the high-side current-sense amplifier to set the LED current. 4 REF +1.23V Reference Output. Connect an appropriate soft-start capacitor from REF to AGND. 5 CS_OUT 6 AGND 7 EN Enable Input/Undervoltage Lockout. Connect EN to IN through a resistive voltage-divider to program the UVLO threshold.
PAGE 8
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control DS HV DD 0.5V DRMP LDOH POR 3.88V H_REG CMP ADIM DGT DIM 1.2X CS+ RAMP 1.1X REF CMP IHI CS- CSA LX LX 1X SRC LV tD = 200ns SRC IN PREG 2.5V VREFI = 1.2V VRAMP = 0.3V BG GT VREF L_REG VDD UVLO/ POR LDOL S Q LATCH DRV G1 1.2V R EN SGND HICCUP REF 1X EN LOGIC CONTROL OSC RT DIM CMP 0.6V ILIM DIM SIGNAL VBE PWM 1.238V CMP X0.
PAGE 9
MAX16812 Detailed Description The MAX16812 is a current-mode PWM LED driver with an integrated 0.2Ω power MOSFET for use in driving HB LEDs. By using two current regulation loops, 5% LED current accuracy is achieved. One current regulation loop controls the internal MOSFET peak current through a sense resistor (RSRC) from SRC to ground, while the other current regulation loop controls the average LED current in a single LED string through another sense resistor (RCS) in series with the LEDs.
PAGE 10
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Undervoltage Lockout The MAX16812 features an adjustable UVLO through the enable input (EN). Connect EN directly to IN to use the 5V default UVLO. Connect EN to IN through a resistive divider to ground to set the UVLO threshold. The MAX16812 is enabled when VEN exceeds the 1.38V (typ) threshold. minimizing output-voltage overshoot. While the part is in UVLO, CREF is discharged (Figure 3).
PAGE 11
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control High-Side Current-Sense Output (CS_OUT) A high-side transconductance amplifier converts the voltage across the LED current-sense resistor (RCS) into an internal current output. This current flows through an internal resistor connected to AGND. The voltage gain for the LED current-sense signal is 4. The amplified signal is then buffered and connected through an internal switch to CS_OUT.
PAGE 12
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Analog Dimming The MAX16812 offers analog dimming of the LED current by allowing the application of an external voltage at REFI. The output current is proportional to the voltage at REFI. Use a potentiometer from REF or directly apply an external voltage source at REFI.
PAGE 13
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control The overvoltage protection (OVP) comparator compares the voltage at OV with a 1.238V (typ) internal reference. Use the following equation to calculate resistorlues:  VOV_LIM − VOV R OV1 = R OV2 x  VOV     where VOV is the 1.238V OV threshold. Choose ROV1 and ROV2 to be reasonably high-value resistors to prevent the discharge of filter capacitors. This prevents degraded performance during dimming.
PAGE 14
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control MAX16812 fig08 MAX16812 fig10 10V/div VOUT VOUT 10V/div 100mA/div 100mA/div ILED 0A, 0V 0A, 0V ILED 2V/div 2V/div VDRV 0V VDRV 10s/div 0V 10s/div Figure 8. LED Current, Output Voltage, and DRV Waveforms when DIM Signal Goes Low Figure 10.
PAGE 15
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control VIN 100k GND TO EN PIN OF MAX16812 TOVER GND 5.1V ZENER MAX6501 TO L_REG PIN OF MAX16812 VCC 4.7F Figure 12. Dimming MOSFET Protection Inductor Selection The minimum required inductance is a function of the operating frequency, the input-to-output voltage differential and the peak-to-peak inductor current (∆IL). Higher ∆IL allows for a lower inductor value while a lower ∆IL requires a higher inductor value.
PAGE 16
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control COUT VIN CIN DOUT CH_REG IN HV RCS LX LV DD DGT CS- CS+ H_REG SRC RSRC EN RRT GT RT CL_REG MAX16812 L_REG RG DRV RTGRM TGRM CTGRM DIM COMP OV VOUT CSLP SLP SGND AGND CREF ROV1 REFI REF CS_OUT FB RCOMP1 CCOMP1 RREF1 ROV2 RCOMP2 RREF2 CCOMP2 Figure 13.
PAGE 17
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control L1 L2 CS CH_REG DOUT RCS RG RT CL_REG COUT GT EN RT MAX16812 L_REG DRV SLP ROV1 RREF1 ROV2 COMP FB CS_OUT REFI REF OV SGND TGRM DIM CTGRM AGND CSLP RTGRM VOUT RSRC SRC IN CIN1 LX HV DD H_REG CS+ LV DGT VIN CS- VIN VOUT RCOMP2 CCOMP1 RCOMP1 RREF2 CCOMP2 Figure 15.
PAGE 18
MAX16812 Layout Recommendations Typically, there are two sources of noise emission in a switching power supply: high di/dt loops and high dv/dt surfaces. For example, traces that carry the drain current often form high di/dt loops. Similarly, the drain of the internal MOSFET connected to the LX pin presents a dv/ dt source. Keep all PCB traces carrying switching currents as short as possible to minimize current loops. Use ground planes for best results.
PAGE 19
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Typical Application Circuit BUCK-BOOST CONFIGURATION CH_REG RCS LV VIN CS- DOUT CS+ DGT DD H_REG HV VOUT GT IN CIN1 RG EN RT DRV RT CL_REG COUT RSRC LX SRC MAX16812 L_REG SLP CSLP RTGRM TGRM CTGRM DIM VOUT OV SGND AGND CS_OUT COMP FB RCOMP1 CREF ROV1 REFI REF CCOMP1 RREF1 ROV2 RCOMP2 RREF2 CCOMP2 Pin Configuration HV H_REG LV 20 GT LX 21 PROCESS: BiCMOS DRV LX TOP VIEW Chip
PAGE 20
MAX16812 Integrated High-Voltage LED Driver with Analog and PWM Dimming Control Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 7/07 Initial release — 1 4/14 No /V OPNs; removed Automotive reference from Applications section 1 DESCRIPTION For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.