MAX16812ATI+T ,Integrated High-Voltage LED Driver with Analog and PWM Dimming ControlApplicationsLV SRCVININ● Architectural and Industrial LightingGTCINENRTDRVMAX16812RTSLPRTGRML_REGCS ..
MAX16814AUP+ ,Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controllerfeatures pulsed dimming control on all ● LCD TV and Desktop Display LED Backlightsfour channels thr ..
MAX16814AUP+T ,Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC ControllerElectrical Characteristics(V = V = 12V, R = 12.25kI, R = 15kI, C = 1FF, V = V , NDRV = COMP = OUT_ ..
MAX16814BUTP+T ,Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC ControllerApplicationssink channels. An integrated current-mode switching • Drives One to Four LED Strings• 4 ..
MAX16814UUP+TCJ3 ,Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controllerapplications.• Internal MOSFET for Each ChannelAn internal current-mode switching DC-DC control- • ..
MAX16815ASA+ ,High-Voltage, 100mA/200mA Adjustable Linear High-Brightness LED Drivers with PWM DimmingElectrical Characteristics(V = 12V, V = 12V (SO only), C = 0.1µF to GND, I = 0, V = 4V, V - = 0V (S ..
MAX4462HESA+ ,SOT23, 3V/5V, Single-Supply, Rail-to-Rail Instrumentation Amplifiers
MAX4462TETT+T ,SOT23, 3V/5V, Single-Supply, Rail-to-Rail Instrumentation Amplifiers
MAX4464EXK ,Single/Dual/Quad, +1.8V/750nA, SC70, Rail-to-Rail Op Amps
MAX4465EUK+T ,Low-Cost, Micropower, SC70/SOT23-8, Microphone Preamplifiers with Complete ShutdownELECTRICAL CHARACTERISTICS(V = +5V, V = 0, V = V /2, R = ∞ to V /2, SHDN = GND (MAX4467/MAX4468 onl ..
MAX4465EUK-T ,Low-Cost / Micropower / SC70/SOT23-8 / Microphone Preamplifiers with Complete ShutdownFeaturesThe MAX4465–MAX4469 are micropower op amps opti- +2.4V to +5.5V Supply Voltage Operationmi ..
MAX4466EUK-T ,Low-Cost / Micropower / SC70/SOT23-8 / Microphone Preamplifiers with Complete ShutdownApplicationsMAX4465EUK-T -40°C to +85°C 5 SOT23-5Microphone PreamplifiersMAX4466EXK-T -40°C to +85° ..
MAX16812ATI+T
Integrated High-Voltage LED Driver with Analog and PWM Dimming Control
General DescriptionThe 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 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 During Dimming
Minimize EMI●Overtemperature and Short-Circuit Protection
Typical Application Circuit and Pin Configuration appear
at end of data sheet.+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PARTTEMP RANGEPIN-PACKAGEMAX16812ATI+-40°C to +125°C28 TQFN-EP*
VIN
CIN
RTGRM
CH_REG
ROV1
ROV2
CTGRM
DIM
TGRM
VOUT
L_REG
RCSDOUT
VOUT
SRC
DRV
SLP
COMP
RCOMP1
BUCK-BOOST CONFIGURATIONCCOMP1
CSLP
RSRC
COUT
RCOMP2
CS-
CS+DGT
H_REGLXSGNDAGNDREFIREFCS_OUTFB
MAX16812
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Simpliied Diagram
Ordering Information
EVALUATION KIT AVAILABLE
(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 ..................................................-0.3V to +6V
LV, HV, CS-, CS+, DGT, DD, H_REG ..................-0.3V to +80V
CS+, DGT, H_REG to LV ......................................-0.3V to +12V
CS- to LV ..............................................................-0.3V to +0.3V
CS+ to CS- ............................................................-0.3V to +12V
DD to LV ...................................................................-1V to +80V
Maximum Current into Any Pin (except LX, SRC) ...........±20mA
Maximum Current into LX and SRC ......................................+2A
Continuous Power Dissipation (TA = +70°C)28-Pin TQFN 5mm x 5mm(derate 34.65mW/°C* above +70°C) .........................2759mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(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.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSInput Voltage RangeVIN5.576.0V
Quiescent SupplyIQVTGRM = 1V, VDIM = 0V0.32.5mA
Shutdown Supply CurrentISHDNVEN ≤ 300mV2045µA
Internal MOSFET On-ResistanceRDSONILX = 1A, VIN > 10V, VGT = VDRV = 5V0.20.4Ω
Output Current AccuracyILEDILED = 350mA, RCS = 1Ω-5+5%
Peak Switch Current LimitILXLIM2.63.13.6A
Hiccup Switch Current6A
Switch Leakage CurrentILXLEAKVEN = 0V, VLX = 76V, VGT = 0V110µA
UNDERVOLTAGE LOCKOUTIN Undervoltage LockoutUVLOVIN rising4.64.95.3V
UVLO Hysteresis100mV
EN Threshold VoltageVEN_THUPVEN rising1.21.381.6V
EN Hysteresis100mV
REFERENCE (REF) AND LOW-SIDE LINEAR REGULATOR (L_REG)Startup Response TimetPORVIN or VEN rising50µs
Reference VoltageVREFIREF = 10µA1.1901.2381.288V
Reference Soft-Start Charging
CurrentIREF_SLEWVREF = 0V254060µA
L_REG Supply VoltageVIN = 7.5V, IL_REG = 1mA4.95.25.5V
L_REG Load RegulationIL_REG = 20mA20Ω
L_REG Dropout VoltageIL_REG = 25mA400mV
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Electrical CharacteristicsStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
*As per JEDEC51 standard (multilayer board).
Absolute Maximum Ratings
(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.)
(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.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
HIGH-SIDE UNDERVOLTAGE LOCKOUT AND LINEAR REGULATOR (H_REG) ((VHV - VLV) = 21V)H_REG Input-Voltage ThresholdVH_REG is rising3.603.8874.20V
H_REG Supply VoltageIH_REG = 04.7555.40V
H_REG Load RegulationIH_REG = 0 to 3mA80Ω
Dropout VoltageIH_REG = 5mA820mV
HIGH-SIDE CURRENT-SENSE AMPLIFIERS (VHV - VLV) = 21VCS- Input Bias CurrentICS-VCS- = VLV, (VCS+ - VCS-) = -0.1V500µA
CS+ Input Bias CurrentICS+VCS- = VLV, (VCS+ - VCS-) = 0.1V-1+1µA
Input Voltage Range VCS- = VLV00.25V
Minimum Output CurrentICS_OUTSinking25µASourcing400
Output Voltage RangeVCS_OUT01.5V
DC Voltage Gain 4V/V
Unity-Gain Bandwidth0.8MHz
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM COMPARATORCOMP Input Leakage CurrentILKCOMPVCOMP = 1V, VSRC = 0.5V, VTGRM = 1V,
VDIM = 0.5V-0.10+0.10µA
SRC Input Leakage CurrentILKSRCVCOMP = 0V, VSRC = 0.5V, VTGRM = 0V,
VDIM = 0.5V-5+5µA
Comparator Offset VoltageVOS(EA)(VCOMP - VSRC) = VOS 860mV
Input Voltage RangeVSRCVCOMP = VSRC + 860mV01.23V
Propagation DelaytPD50mV overdrive100ns
ERROR AMPLIFIERFB Input CurrentVFB = 1V, VREFI = 1.2V-100+100nA
REFI Input CurrentVFB = 1V, VREFI = 1V-100+100nA
Error-Amplifier Offset VoltageVOSVFB = VCOMP = 1.2V-23+23mV
Input Common-Mode RangeVFB = (VCOMP - 0.9V)01.5V
Source CurrentICOMP(VREFI - VFB) ≥ 0.5V300µA
Sink Current(VFB - VREFI) ≥ 0.5V80µA
COMP Clamp VoltageVCOMPVREF = 1.2V, VFB = 0V1.202.56V
DC Gain72dB
Unity-Gain Bandwidth0.8MHz
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Electrical Characteristics
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.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
HIGH-SIDE DIMMING LINEAR REGULATOR ((VHV - VLV) = 21V)Minimum Output CurrentIDGT
VLV = VCS-, (VCS+ - VCS-) = 0.3V,
(VDD - VLV) = 1V, VDIM = 1V, VTGRM = 0V,
VDGT = 1V, VREFI = 1.0V, sinking
VLV = VCS-, (VCS+ - VCS-) = 0.2V,
(VDD - VLV) = 1V, VTGRM = 0V, VDGT = 3V,
VREFI = 1.0V, VDIM = 1V, sourcing
Output Voltage Range0.25.0V
DC Gain CDGT = 1nF to LV60dB
DD Input Bias CurrentIDD(VDD - VCS-) = 0.5V-3+3µA
DD Input Low ThresholdVTGRM = 0V, VDIM = 1V, VREFI = 1.2V,
(VDGT - VLV) > 1.5V, VDD falling0.250.500.75V
DIMMING ((VHV - VLV) = 21V)DIM Input Bias CurrentIDIMVDIM = 1.1V-1+1µA
TGRM Input High Threshold1.181.231.27V
TGRM Reset High-to-TGRM Low
Pulse Width1µs
TGRM Reset Switch RDS(ON)VTGRM = 1.3V20Ω
Dimming Rise and Fall LED
Current Times5µs
OVERVOLTAGE PROTECTION (OV)OV Input High ThresholdVOV rising1.1801.2301.292V
OV Input Threshold Hysteresis14mV
OV Input Bias CurrentIOVVOV = 1.1V-1+1µA
INTERNAL OSCILLATOR CLOCKInternal Clock FrequencyfOSCRT = 2MΩ to AGND470525570kHzRT = 50kΩ to AGND105125155
SLOPE COMPENSATION INPUT (SLP) SLP Input CurrentISLPVSLP = 0V150µA
LOW-SIDE GATE DRIVE (DRV) DRV Output Low ImpedanceRDRV_LODRV sinking 20mA330Ω
DRV Output High ImpedanceRDRV_HIDRV sourcing 20mA1045Ω
INTERNAL POWER MOSFETGT Input Leakage CurrentVGT = 0 to 5V-1+1µA
Internal MOSFET Gate-to-
Source Threshold VoltageVTH2.5V
Internal MOSFET Gate ChargeQgVLX = 50V8nC
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Electrical Characteristics (continued)
(VIN = VEN = 12V, CL_REG = 3.3µF, CH_REG = 1µF, VTGRM = 0V, TA = +25°C, unless otherwise noted.)
EN UVLO THRESHOLD
vs. TEMPERATUREMAX16812 toc08
EN UVLO (V)
VEN RISING
IN UVLO THRESHOLD
vs. TEMPERATUREMAX16812 toc07
IN UVLO (V)
VIN FALLING
IN UVLO THRESHOLD
vs. TEMPERATUREMAX16812 toc06
TEMPERATURE (°C)
IN UVLO THRESHOLD (V)
VIN RISING
VREF vs. TEMPERATUREMAX16812 toc05
TEMPERATURE (°C)
REF
(V)
IREF = 10µA
SHUTDOWN CURRENT
vs. TEMPERATUREMAX16812 toc04
TEMPERATURE (°C)
SHUTDOWN CURRENT (
SWITCH CURRENT LIMIT
vs. TEMPERATURE
MAX16812 toc03
TEMPERATURE (°C)
SWITCH CURRENT LIMIT (A)
RDS(ON) vs. VGT
MAX16812 toc02
VGT (V)
DS(ON)
TA = +25C
RDS(ON) vs. ILXMAX16812 toc01
ILX (A)
DS(ON)
TA = +125C
TA = +25C
TA = -40C
MAX16812Integrated 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.)
VH_REG vs. TEMPERATUREMAX16812 toc15
TEMPERATURE (°C)
H_REG
(V)
(VHV - VLV) = 21V
ILOAD = 3mA
VH_REG vs. IH_REGMAX16812 toc14
IH_REG (mA)
H_REG
(V)
(VHV - VLV) = 6V
VIN = 12V
VH_REG IS MEASURED
WITH RESPECT TO VLV
VH_REG THRESHOLD
vs. TEMPERATUREMAX16812 toc13
TEMPERATURE (°C)
H_REG
THRESHOLD (V)
OSCILLATOR FREQUENCY vs. RT
MAX16812 toc12
RT (MΩ)
OSCILLATOR FREQUENCY (kHz)0.1
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX16812 toc11
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
RT = 2MΩ
RT = 180kΩ
RT = 50kΩ
VL_REG vs. IL_REGMAX16812 toc10
IL_REG (mA)
L_REG
(V)161214468102
TA = +125C
TA = +25C
TA = -40C
VIN = 7.5V
EN UVLO THRESHOLD
vs. TEMPERATUREMAX16812 toc09
TEMPERATURE (°C)
EN UVLO (V)
VEN FALLING
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Typical Operating Characteristics (continued)
PINNAMEFUNCTIONFBLow-Side Error Amplifier’s Inverting InputCOMPLow-Side Error Amplifier’s Output. Connect a compensation network from COMP to FB for stable operation.REFIReference Input. VREFI provides the reference voltage for the high-side current-sense amplifier to set the
LED current.REF+1.23V Reference Output. Connect an appropriate soft-start capacitor from REF to AGND.CS_OUTHigh-Side Current-Sense Amplifier Output. VCS_OUT is proportional to the current through RCS. AGNDAnalog GroundEN
Enable Input/Undervoltage Lockout. Connect EN to IN through a resistive voltage-divider to program the
UVLO threshold. Connect EN directly to IN to set up the device for 5V internal threshold. Apply a logic-level
input to EN to enable/disable the device.INPositive Power-Supply Input. Bypass with a 1µF ceramic capacitor to AGND. L_REG5V Low-Side Regulator Output. Bypass with a 3.3µF ceramic capacitor to AGND.SGNDSignal GroundDDMOSFET’s Drain Voltage-Sense Input. Connect DD to the drain of the external dimming MOSFET.DGTExternal Dimming MOSFET’s Gate DriveCS+High-Side Current-Sense Amplifier’s Positive Input. Connect RCS between CS+ and CS-. CS+ is
referenced to LV.CS-High-Side Current-Sense Amplifier’s Negative Input. Connect RCS between CS- and CS+. CS- is
referenced to LV.LVHigh-Side Reference Voltage Input. A DC voltage at LV sets the lowest reference point for the high-side
current-sense and dimming MOSFET control circuitry.H_REGHigh-Side Regulator Output. H_REG provides a regulated supply for high-side circuitry. Bypass with a 1µF
ceramic capacitor to LV. HVHigh-Side Positive Supply Voltage Input. HV provides power for dimming and LED current-sense circuitry.
HV is referenced to LV.DRVInternal MOSFET Gate Driver Output. Connect to a resistor between DRV and GT to set the rise and fall
times at LX. GTInternal MOSFET GATE. Connect a resistor between GT and DRV to set the rise and fall times at LX.
20, 21LXInternal MOSFET Drain
22, 23SRCInternal Power MOSFET SourceSLPSlope Compensation Setting. Connect an appropriate external capacitor from SLP to AGND to generate a
ramp signal for stable operation.TGRMDimming Comparator’s Reference/Ramp GeneratorDIMDimming Control InputRTResistor-Programmable Internal Oscillator Setting. Connect a resistor from RT to AGND to set the internal
oscillator frequency. OV
Overvoltage Protection Input. Connect OV to HI through a resistive voltage-divider to AGND to set the
overvoltage limit for the load. When the voltage at OV exceeds the 1.238V (typ) threshold, the gate drive
(DRV) for the switching MOSFET is disabled. Once VOV goes below 1.238V by 14mV, the switching
MOSFET turns on again.Exposed Pad. Connect EP to a large-area ground plane for effective power dissipation. Do not use as the
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Pin Description
Figure 1. Functional Diagram
LDOH
POR
3.88V1.2X
1.1X
PREGBG
VREF
LDOL
OSC
tD = 200ns
UVLO/
POR
DIM
RAMP
REF
CMP
CMP
IHICSA
ADIM
DRMP
0.5VLATCHS
LOGIC
CONTROL
ERROR
AMPLIFIER
AND
DIMMING
S/H
VREFI = 1.2V
VRAMP = 0.3V
CMP
OVP
CMP
1.238V
1.238V
2µs PULSE
LOW TO DISCHARGE
DIM
SIGNAL
2.5V
VDD
1.2V
SGND
HICCUP
0.6V
ILIM
PWM
VBE
X0.2
MAX16812
H_REG
L_REG
REF
DIM
TGRM
SGNDAGND
CS+
CS-
SRC
SRC
DRV
SLP
COMP
CS_OUT
REFI
DGT
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Detailed DescriptionThe 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 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.
The MAX16812 includes a cycle-by-cycle current limit
that turns off the gate drive to the internal MOSFET
during an overcurrent condition. The MAX16812 features programmable oscillator that simplifies and optimizes
the design of magnetics. The MAX16812 is well suited
for inputs from 5.5V to 76V. An external resistor in series
with the internal MOSFET gate can control the rise and
fall times on the drain of the internal switching MOSFET,
therefore minimizing EMI problems.
The MAX16812 high-frequency, current-mode PWM
HB LED driver integrates all the necessary building blocks
for driving a series LED string in an adjustable constant
current mode with PWM dimming. Current-mode control
with leading-edge blanking simplifies control-loop design,
and an external adjustable slope-compensation control
stabilizes the inner current-mode loop when operating at
duty cycles above 50%.
An input undervoltage lockout (UVLO) programs the input
supply startup voltage. An external voltage-divider on
EN programs the supply startup voltage. If EN is directly
connected to the input, the UVLO is set at 5V. A single
external resistor from RT to AGND programs the switch-
ing frequency from 125kHz to 500kHz.
Wide contrast (100:1) PWM dimming can be achieved
with the MAX16812. A DC input on DIM controls the
dimming duty cycle. The dimming frequency is set by
the sawtooth ramp frequency on TGRM (see the PWM
Dimming section). In addition, PWM dimming can be
achieved by applying a PWM signal to DIM with TGRM
set to a DC voltage less than 1.238V. A floating high-volt-
age driver drives an external n-channel MOSFET in series
with the LED string. REFI allows analog dimming of the
LED current, further increasing the effective dimming
range over PWM alone. The MAX16812 has a 5µs pre-
programmed LED current rise and fall time.
A nonlatching overvoltage protection limits the voltage on
the internal switching MOSFET under open-circuit condi-
tions in the LED string. The internal thermal shutdown cir-
Current-Mode ControlThe MAX16812 offers a current-mode control opera-
tion feature with leading-edge blanking that blanks the
sensed current signal applied to the input of the PWM
current-mode comparator. In addition, a current-limit com-
parator monitors the same signal at all times and provides
cycle-by-cycle current limit. An additional hiccup com-
parator limits the absolute peak current to two times the
cycle-by-cycle current limit. The leading-edge blanking of
the current-sense signal prevents noise at the PWM com-
parator input from prematurely terminating the on-cycle.
The switch current-sense signal contains a leading-edge
spike that results from the MOSFET gate-charge current,
and the capacitive and diode reverse-recovery current of
the power circuit. The MAX16812’s capacitor-adjustable
slope-compensation feature allows for easy stabilization
of the inner switching MOSFET current-mode loop. Upon
triggering the hiccup current limit, the soft-start capacitor
on REF is discharged and the gate drive to DRV is dis-
abled. Once the inductor current falls below the hiccup
current limit, the soft-start capacitor is released and it
begins to charge after 10µs.
Slope CompensationThe MAX16812 uses an internal ramp generator for
slope compensation. The internal ramp signal resets at
the beginning of each cycle and slews at the rate pro-
grammed by the external capacitor connected at SLP
and an internal ISLP current source of 150µA. An internal
attenuator attenuates the actual slope compensation
signal by a factor of 0.2. Adjust the MAX16812 slew-rate
capacitor by using the following equation:
SLPSLOPEC 0.2 SR=×
where ISLP is the charging current in mA and CSLOPE is
the slope compensation capacitance on the SLP in µF,
and SR is the designed slope in mV/µs.
When using the MAX16812 for internal switching MOSFET
duty cycles greater than 50%, the following conditions
must be met to avoid current-loop subharmonic oscilla-
tions.
SRCIND_OFF0.5 R VSR mV/sL××≥µ
where RSRC is in mΩ, VIND_OFF is in volts, and L is in
µH. L is the inductor connected to the LX pin of the
internal switching MOSFET and VIND_OFF is the voltage
across the inductor during the off-time of the internal
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
Undervoltage LockoutThe 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 divid-
er to ground to set the UVLO threshold. The MAX16812
is enabled when VEN exceeds the 1.38V (typ) threshold.
Calculate the EN UVLO resistor-divider values as follows
(see Figure 2):UV1UV2UVLOENR R x V- V=
where RUV1 is in the 20kΩ range, VEN is the 1.38V
(typ) EN threshold voltage, and VUVLO is the desired
input-voltage UVLO threshold in volts. Due to the 100mV
hysteresis of the UVLO threshold, capacitor CEN is
required to prevent chattering at the UVLO threshold due
to line impedance drops at power-up and during dimming.
If the undervoltage setting is very close to the required
minimum operating voltage, there can be jumps in the
voltage at IN while dimming. CEN should be large enough
to limit the ripple on EN to less than 100mV (EN hystere-
sis) under these conditions so that it does not turn on and
off due to the ripple on IN.
Soft-StartThe soft-start feature of the MAX16812 allows the LED
string current to ramp up in a controlled manner, thus
minimizing output-voltage overshoot. While the part is in
UVLO, CREF is discharged (Figure 3). Upon coming out
of UVLO, an internal current source starts charging CREF
during the soft-start cycle. Use the following equation to
calculate total soft-start e:REF
REF
1.238t C I=×
where IREF is 40µA, CREF is in µF, and tST is in seconds.
Operation begins when REF ramps above 0.6V. Once
the soft-start is complete, REF is regulated to 1.238V, the
internal voltage reference.
Low-Side Internal Switching MOSFET Driver Supply (L_REG)L_REG is the regulated (5.2V) internal supply voltage
capable of delivering 20mA. L_REG provides power to
the gate drive of the internal switching power MOSFET.
VL_REG is referenced to AGND. Connect a 3.3µF ceramic
capacitor from L_REG to AGND.
High-Side Regulator (H_REG)H_REG is a low-dropout linear regulator referenced
to LV. H_REG provides the gate drive for the external
n-channel dimming MOSFET and also powers up the
MAX16812’s LED current-sense circuitry. Bypass H_REG
to LV with a 1µF ceramic capacitor.
Figure 3. Soft-Start SettingFigure 2. UVLO Threshold Setting
MAX16812
VIN
AGND
REF
CREF
MAX16812
VIN
AGND
RUV2
RUV1CEN
MAX16812Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
