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MAX16801AEUA+ |MAX16801AEUAMAXIMN/a93avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers
MAX16801BEUA+ |MAX16801BEUAMAXIMN/a56avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers
MAX16801BEUA+TMAXIMN/a19992avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers
MAX16802AEUA+ |MAX16802AEUAMAXIMN/a41avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers
MAX16802BEUA+MAIXMN/a1500avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers
MAX16802BEUA+TMAXN/a5000avaiOffline and DC-DC PWM Controllers for High-Brightness LED Drivers


MAX16801BEUA+T ,Offline and DC-DC PWM Controllers for High-Brightness LED DriversFeaturesThe MAX16801A/B/MAX16802A/B high-brightness (HB) ♦ Suitable for Buck, Boost, Flyback, SEPIC ..
MAX16802AEUA+ ,Offline and DC-DC PWM Controllers for High-Brightness LED DriversApplicationsMAX16801AEUA+ -40°C to +85°C 8 µMAXOffline and DC-DC LED Commercial andMAX16801BEUA+ -4 ..
MAX16802BEUA+ ,Offline and DC-DC PWM Controllers for High-Brightness LED DriversFeaturesThe MAX16801A/B/MAX16802A/B high-brightness (HB) ♦ Suitable for Buck, Boost, Flyback, SEPIC ..
MAX16802BEUA+T ,Offline and DC-DC PWM Controllers for High-Brightness LED Driversapplications. The♦ Universal Offline Input Voltage Range: RectifiedMAX16801 is well suited for univ ..
MAX16804ATP+ ,High-Voltage, 350mA, High-Brightness LED Driver with Analog and PWM Dimming ControlElectrical Characteristics(V = V = 12V, C = 0.1μF, I = 0, CS- = GND, R = 0.56Ω (see the Typical Ope ..
MAX16804ATP+T ,High-Voltage, 350mA, High-Brightness LED Driver with Analog and PWM Dimming ControlApplicationsLosses● Warning Lights for Emergency Vehicles● Thermal Shutdown and Output Short-Circui ..
MAX4453ESA ,Low-Cost / +3V/+5V / 620A / 200MHz / Single-Supply Op Amps with Rail-to-Rail OutputsELECTRICAL CHARACTERISTICS(V = +5V, V = V /2 - 0.75V, V = 0, R = ∞ to V /2, V = V /2, T = T to T , ..
MAX4453ESA+T ,Low-Cost, +3V/+5V, 620µA, 200MHz, Single-Supply Op Amps with Rail-to-Rail OutputsFeaturesThe MAX4452/MAX4352 single, MAX4453/MAX4353♦ Ultra-Low 620µA Supply Currentdual, and MAX445 ..
MAX4454EUD+ ,Low-Cost, +3V/+5V, 620µA, 200MHz, Single-Supply Op Amps with Rail-to-Rail OutputsApplicationsM A X44 5 3 E KA-T - 40° C to + 85° C 8 SOT 23- 8 AAD S Battery-Powered InstrumentsM ..
MAX4456CPL ,Low-Cost 4x4 / 8x4 / 8x8 Video Crosspoint SwitchesFeaturesThe MAX4359/MAX4360/MAX4456 low-cost video cross- Eight (MAX4456) or Four (MAX4359/MAX4360 ..
MAX4456CPL ,Low-Cost 4x4 / 8x4 / 8x8 Video Crosspoint SwitchesMAX4359/MAX4360/MAX445619-1389; Rev 1; 12/99Low-Cost 4x4, 8x4, 8x8Video Crosspoint Switches
MAX4456CPL+ ,Low-Cost 4x4, 8x4, 8x8 Video Crosspoint SwitchesELECTRICAL CHARACTERISTICS(V+ = +5V, V- = -5V, V = +5V (internal load resistors on), V = V = V = 0V ..


MAX16801AEUA+-MAX16801BEUA+-MAX16801BEUA+T-MAX16802AEUA+-MAX16802BEUA+-MAX16802BEUA+T
Offline and DC-DC PWM Controllers for High-Brightness LED Drivers
General Description
The MAX16801A/B/MAX16802A/B high-brightness (HB)
LED driver-control ICs contain all the circuitry required
for the design of wide-input-voltage-range LED drivers
for general lighting and display applications. The
MAX16801 is well suited for universal input (rectified
85VAC to 265VAC) LED drivers, while the MAX16802 is
intended for low-input-voltage (10.8VDC to 24VDC) LED
drivers.
When the LED current needs to be tightly regulated, an
additional on-board error amplifier with 1% accurate ref-
erence can be utilized. A wide dimming range can be
implemented by using low-frequency PWM dimming.
The MAX16801/MAX16802 feature an input undervoltage
lockout (UVLO) for programming the input-supply start
voltage, and to ensure proper operation during brownout
conditions. The MAX16801 has an internal-bootstrap
undervoltage lockout circuit with a large hysteresis that
simplifies offline LED driver designs. The MAX16802 does
not have this internal bootstrap circuit and can be biased
directly from a +12V rail.
The 262kHz fixed switching frequency is internally
trimmed, allowing for optimization of the magnetic and fil-
ter components, resulting in a compact, cost-effective
LED driver. The MAX16801A/MAX16802A areofferedwith
50%maximum duty cycle.The MAX16801B/MAX16802B
are offered with 75% maximum duty cycle. These devices
are available in an 8-pin µMAX®package and operate
over the -40°C to +85°C temperature range.
Applications
Features
Suitable for Buck, Boost, Flyback, SEPIC, and
Other Topologies
Up to 50W or Higher Output PowerUniversal Offline Input Voltage Range: Rectified
85VAC to 265VAC (MAX16801)
IN Pin Directly Driven From 10.8VDC to 24VDC
Input (MAX16802)
Internal Error Amplifier with 1% Accurate
Reference for Precise LED Current Regulation
PWM or Linear DimmingFixed Switching Frequency of 262kHz ±12%Thermal ShutdownDigital Soft-StartProgrammable Input Startup VoltageInternal Bootstrap UVLO with Large Hysteresis
(MAX16801)
45µA (typ) Startup Supply Current, 1.4mA (typ)
Operating Supply Current
50% (MAX16801A/MAX16802A) or 75%
(MAX16801B/MAX16802B) Maximum Duty Cycle
Available in a Tiny 8-Pin µMAX Package
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
Ordering Information

19-3880; Rev 2; 1/10
PARTTEMP
RANGE
PIN-
PACKAGE
MAX16801AEUA+
-40°C to +85°C8 µMAX
MAX16801BEUA+-40°C to +85°C8 µMAX
MAX16802AEUA+
-40°C to +85°C8 µMAX
MAX16802BEUA+-40°C to +85°C8 µMAX
+Denotes lead-free package.
Offline and DC-DC LED
Drivers
RGB Back Light for LCD
TVs and Monitors
Commercial and
Industrial Lighting
Decorative and
Architectural Lighting
EVALUATION KIT
AVAILABLE

MAX16802B
10.8VDC TO 24VDC
PWM
GNDR1LEDs
COMP
DIM/FB
UVLO/ENIN
VCC
NDRV
GND
ENABLE
Typical Operating Circuit

µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VIN= +12V (MAX16801: VINmust first be brought up to +23.6V for startup), 10nF bypass capacitors at IN and VCC, CNDRV= 0µF,
VUVLO= +1.4V, VDIM/FB= +1.0V, COMP = unconnected, VCS= 0V, TA= -40°C to +85°C, unless otherwise noted. Typical values are
at TA= +25°C.) (Note 1)
Stresses 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.
IN to GND..........................................................................-0.3V to +30V
VCCto GND......................................................................-0.3V to +13V
DIM/FB, COMP, UVLO, CS to GND..........................-0.3V to +6V
NDRV to GND.............................................-0.3V to (VCC+ 0.3V)
Continuous Power Dissipation (TA = +70°C)
8-Pin µMAX (derate 4.5mW/°C above +70°C)..............362mW
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
UNDERVOLTAGE LOCKOUT/STARTUP

Bootstrap UVLO Wake-Up LevelVSUVRVIN rising (MAX16801 only)19.6821.623.60V
Bootstrap UVLO Shutdown LevelVSUVFVIN falling (MAX16801 only)9.059.7410.43V
UVLO/EN Wake-Up ThresholdVULR2UVLO/EN rising1.1881.281.371V
UVLO/EN Shutdown ThresholdVULF2UVLO/EN falling1.1681.231.291V
UVLO/EN Input CurrentIUVLOTJ = +125°C25nA
UVLO/EN Hysteresis50mV
IN Supply Current In
Undervoltage LockoutISTARTVIN = +19V, for MAX16801 only when in
bootstrap UVLO4590µA
IN Voltage RangeVIN10.824V
tEXTRUVLO/EN steps up from +1.1V to +1.4V12UVLO/EN Propagation DelaytEXTFUVLO/EN steps down from +1.4V to +1.1V1.8µs
tBUVRVIN steps up from +9V to +24V5Bootstrap UVLO Propagation
DelaytBUVFVIN steps down from +24V to +9V1µs
INTERNAL SUPPLY

VCC Regulator Set PointVCCSPVIN = +10.8V to +24V, sinking 1µA to 20mA
from VCC710.5V
IN Supply Current After StartupIINVIN = +24V1.42.5mA
Shutdown Supply CurrentUVLO/EN = low90µA
GATE DRIVER

RON(LOW)Measured at NDRV sinking, 100mA24Driver Output ImpedanceRON(HIGH)Measured at NDRV sourcing, 20mA412Ω
Driver Peak Sink Current1A
Driver Peak Source Current0.65A
PWM COMPARATOR

Comparator Offset VoltageVOPWMVCOMP - VCS1.151.381.70V
CS Input Bias CurrentICSVCS = 0V-2+2µA
Comparator Propagation DelaytPWMVCS = +0.1V60ns
Minimum On-TimetON(MIN)150ns
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
Note 1:
All devices are 100% tested at TA= +85°C. All limits over temperature are guaranteed by characterization.
Note 2:
VREF is measured with DIM/FB connected to the COMP pin (see the Functional Diagram).
Note 3:
The MAX16801 is intended for use in universal input offline drivers. The internal clamp circuit is used to prevent the boot-
strap capacitor (C1 in Figure 5) from charging to a voltage beyond the absolute maximum rating of the device when
EN/UVLO is low. The maximum current to IN (hence to clamp) when UVLO is low (device in shutdown), must be externally
limited to 2mA (max). Clamp currents higher than 2mA may result in clamp voltage higher than +30V, thus exceeding the
absolute maximum rating for IN. For the MAX16802, do not exceed the +24V maximum operating voltage of the device.
ELECTRICAL CHARACTERISTICS (continued)

(VIN= +12V (MAX16801: VINmust first be brought up to +23.6V for startup), 10nF bypass capacitors at IN and VCC, CNDRV= 0µF,
VUVLO= +1.4V, VDIM/FB= +1.0V, COMP = unconnected, VCS= 0V, TA= -40°C to +85°C, unless otherwise noted. Typical values are
at TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
CURRENT-SENSE COMPARATOR

Current-Sense Trip ThresholdVCS262291320mV
CS Input Bias CurrentICSVCS = 0V-2+2µA
Propagation Delay From
Comparator Input to NDRVtPWM50mV overdrive60ns
Switching FrequencyfSW230262290kHz
MAX1680_A5050.5Maximum Duty CycleDMAXMAX1680_B7576%
IN CLAMP VOLTAGE

IN Clamp VoltageVINC2mA sink current, MAX16801 only (Note 3)24.126.129.0V
ERROR AMPLIFIER

Voltage GainRLOAD = 100kΩ80dB
Unity-Gain BandwidthRLOAD = 100kΩ, CLOAD = 200pF2MHz
Phase MarginRLOAD = 100kΩ, CLOAD = 200pF65D eg r ees
DIM/FB Input Offset Voltage3mV
High2.23.5COMP Clamp VoltageLow0.41.1V
Source Current0.5mA
Sink Current0.5mA
Reference VoltageVREF(Note 2)1.2181.2301.242V
Input Bias Current50nA
COMP Short-Circuit Current8mA
THERMAL SHUTDOWN

Thermal-Shutdown Temperature130°C
Thermal Hysteresis25°C
DIGITAL SOFT-START

Soft-Start Duration15,872Clock
cycles
Reference Voltage Steps During
Soft-Start31Steps
Reference Voltage Step40mV
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
Typical Operating Characteristics

(VUVLO/EN= +1.4V, VFB= +1V, COMP = unconnected, VCS= 0V, TA= +25°C, unless otherwise noted.)
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE

MAX16801 toc01
TEMPERATURE (°C)
(V)40200-20
MAX16801 VIN RISING
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE

MAX16801 toc02
TEMPERATURE (°C)
(V)40200-20
MAX16801 VIN FALLING
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE

MAX16801 toc03
TEMPERATURE (°C)
UVLO/EN (V)40200-20
UVLO/EN RISING
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE

MAX16801 toc04
TEMPERATURE (°C)
UVLO/EN (V)40200-20
UVLO/EN FALLING
VIN SUPPLY CURRENT IN UNDERVOLTAGE
LOCKOUT vs. TEMPERATURE

MAX16801 toc05
TEMPERATURE (°C)
START40200-20
VIN = 19V
MAX16801 WHEN IN BOOTSTRAP UVLO
MAX16802 WHEN UVLO/EN IS LOW
VIN SUPPLY CURRENT AFTER STARTUP
vs. TEMPERATURE

MAX16801 toc06
TEMPERATURE (°C)
IIN
(mA)40200-20
VIN = 24V
VCC REGULATOR SET POINT
vs. TEMPERATURE

MAX16801 toc07
TEMPERATURE (°C)
(V)40200-20
VIN = 19V
NO LOAD
NDRV OUTPUT IS NOT
SWITCHING, VFB = 1.5V
NDRV OUTPUT IS
SWITCHING
VCC REGULATOR SET POINT
vs. TEMPERATURE

MAX116801 toc08
TEMPERATURE (°C)
(V)40200-20
VIN = 10.8V
10mA LOAD
20mA LOAD
CURRENT-SENSE THRESHOLD
vs. TEMPERATURE

MAX16801 toc09
TEMPERATURE (°C)
CURRENT-SENSE THRESHOLD (40200-20
+3σ
-3σ
MEAN
TOTAL NUMBER OF
DEVICES = 100
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
CURRENT-SENSE THRESHOLD

MAX16801 toc10
CURRENT-SENSE THRESHOLD (mV)
PERCENTAGE OF UNITS (%)
TOTAL NUMBER OF
DEVICES = 200
SWITCHING FREQUENCY
vs. TEMPERATURE

MAX16801 toc11
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)40200-20
+3σ
-3σ
MEAN
TOTAL NUMBER OF
DEVICES = 100
SWITCHING FREQUENCY

MAX16801 toc12
SWITCHING FREQUENCY (kHz)
PERCENTAGE OF UNITS (%)
TOTAL NUMBER OF
DEVICES = 200
PROPAGATION DELAY FROM
CURRENT-SENSE COMPARATOR INPUT
TO NDRV vs. TEMPERATURE

MAX16801 toc13
TEMPERATURE (°C)
PWM
(ns)40200-20
UVLO/EN PROPAGATION DELAY
vs. TEMPERATURE
MAX16801 toc14
TEMPERATURE (°C)
UNDERVOLTAGE LOCKOUT DELAY (40200-20
UVLO/EN RISING
UVLO/EN FALLING
REFERENCE VOLTAGE
vs. TEMPERATURE

MAX16801 toc15
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)40200-20
VIN = 12V
INPUT CURRENT
vs. INPUT CLAMP VOLTAGE

MAX16801 toc16
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
MAX16801 toc17
TEMPERATURE (°C)
INPUT CLAMP VOLTAGE (V)40200-20
IIN = 2mA
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE

MAX16801 toc18
TEMPERATURE (°C)40200-20
VIN = 24V
SINKING 100mA
Typical Operating Characteristics (continued)

(VUVLO/EN= +1.4V, VFB= +1V, COMP = unconnected, VCS= 0V, TA= +25°C, unless otherwise noted.)
MAX16801A/B/MAX16802A/B
Detailed Description

The MAX16801/MAX16802 family of devices is intend-
ed for constant current drive of high-brightness (HB)
LEDs used in general lighting and display applications.
They are specifically designed for use in isolated and
nonisolated circuit topologies such as buck, boost, fly-
back, and SEPIC, operating in continuous or discontin-
uous mode. Current mode control is implemented with
an internally trimmed, fixed 262kHz switching frequen-
cy. A bootstrap UVLO with a large hysteresis (11.9V),
very low startup current, and low operating current
result in an efficient universal-input LED driver. In addi-
tion to the internal bootstrap UVLO, these devices also
offer programmable input startup voltage programmed
through the UVLO/EN pin. The MAX16801 is well suited
for universal AC input (rectified 85VAC to 265VAC) dri-
vers. The MAX16802 is well suited for low input voltage
(10.8VDC to 24VDC) applications.
The MAX16801/MAX16802 regulate the LED current by
monitoring current through the external MOSFET cycle
by cycle.
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers
Pin Description
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE

MAX16801 toc19
TEMPERATURE (°C)40200-20
VIN = 24V
SOURCING 20mA
ERROR-AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY

MAX16801 toc20
FREQUENCY (Hz)
GAIN (dB)
10M1M10k1k100k101001
PHASE (DEGREES)
0.1100M
GAIN
PHASE
Typical Operating Characteristics (continued)

(VUVLO/EN= +1.4V, VFB= +1V, COMP = unconnected, VCS= 0V, TA= +25°C, unless otherwise noted.)
PINNAMEFUNCTION
UVLO/ENExternally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect
UVLO to GND to disable the device.DIM/FBLow-Frequency PWM Dimming Input/Error-Amplifier Inverting InputCOMPError-Amplifier Output. Connect the compensation components between DIM/FB and COMP in high-
accuracy LED current regulation.
4CSCurrent-Sense Connection for Current Regulation. Connect to high side of sense resistor. An RC filter
may be necessary to eliminate leading-edge spikes.GNDPower-Supply GroundNDRVExternal n-Channel MOSFET Gate Connection
7VCCGate-Drive Supply. Internally regulated down from IN. Decouple with a 10nF or larger capacitor to GND.
8IN
IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX16801),
connect a startup resistor from the input supply line to IN. Connect the bias winding supply to this point
(see Figure 5). For the MAX16802, connect IN directly to a +10.8V to +24V supply.
When in the bootstrapped mode with a transformer
(Figure 5), the circuit is protected against most output
short-circuit faults when the tertiary voltage drops
below +10V, causing the UVLO to turn off the gate
drive of the external MOSFET. This re-initiates a startup
sequence with soft-start.
When the LED current needs to be tightly regulated, an
internal error amplifier with 1% accurate reference can
be used (Figure 9). This additional feedback minimizes
the impact of passive circuit component variations and
tolerances, and can be implemented with a minimum
number of additional external components.
A wide dimming range can be implemented using a
low-frequency PWM dimming signal fed directly to the
DIM/FB pin.
LED driver circuits designed with the MAX16801 use a
high-value startup resistor R1 that charges a reservoir
capacitor C1 (Figure 5 or Figure 9). During this initial
period, while the voltage is less than the internal boot-
strap UVLO threshold, the device typically consumes
only 45µA of quiescent current. This low startup current
and the large bootstrap UVLO hysteresis help minimize
the power dissipation across R1, even at the high end
of the universal AC input voltage.
An internal shutdown circuit protects the device when-
ever the junction temperature exceeds +130°C (typ).
Dimming

Linear dimming can be implemented by creating a
summing node at CS, as shown in Figures 6 and 7.
Low-frequency PWM (chopped-current) dimming is
possible by applying an inverted-logic PWM signal to
the DIM/FB pin of the IC (Figure 8). This might be a pre-
ferred way of dimming in situations where it is critical to
retain the light spectrum unchanged. It is accom-
plished by keeping constant the amplitude of the
chopped LED current.
MAX16801/MAX16802 Biasing

Implement bootstrapping from the transformer when it
is present (Figure 5). Biasing can also be realized
directly from the LEDs in non-isolated topologies
(Figure 1).
Bias the MAX16802 directly from the input voltage of
10.8VDC to 24VDC. The MAX16802 can also be used
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers

MAX16801BAC
BRIDGE
RECTIFIERR5
VCCNDRV
COMP
DIM/FB
UVLO/ENGNDC3
TOTAL LED VOLTAGE:
11V TO 23V
Figure 1. Biasing the IC using LEDs in Nonisolated Flyback Driver
in applications with higher input DC voltages by imple-
menting resistor-Zener bias (Figure 2a) or transistor-
Zener-resistor bias (Figure 2b).
MAX16801/MAX16802 Undervoltage
Lockout

The MAX16801/MAX16802 have an input voltage
UVLO/EN pin. The threshold of this UVLO is +1.28V.
Before any operation can commence, the voltage on
this pin has to exceed +1.28V. The UVLO circuit keeps
the CPWM comparator, ILIM comparator, oscillator,
and output driver in shutdown to reduce current con-
sumption (see the Functional Diagram). Use this UVLO
function to program the input start voltage. Calculate
the divider resistor values, R2 and R3 (Figure 5), by
using the following formulas:
The value of R3 is calculated to minimize the voltage-
drop error across R2 as a result of the input bias cur-
rent of the UVLO/EN pin. VULR2 = +1.28V, IUVLO =
50nA (max), VINis the value of the input-supply voltage
where the power supply must start.
where IUVLOis the UVLO/EN pin input current, and
VULR2is the UVLO/EN wake-up threshold.
MAX16801 Bootstrap Undervoltage
Lockout

In addition to the externally programmable UVLO func-
tion offered in both the MAX16801/MAX16802, the
MAX16801 has an additional internal bootstrap UVLO
that is very useful when designing high-voltage LED
drivers (see the Functional Diagram). This allows the
device to bootstrap itself during initial power-up. The
MAX16801 attempts to start when VINexceeds the
bootstrap UVLO threshold of +23.6V. During startup,
the UVLO circuit keeps the CPWM comparator, ILIM
comparator, oscillator, and output driver shut down to
reduce current consumption. Once VINreaches
+23.6V, the UVLO circuit turns on both the CPWM and
ILIM comparators, as well as the oscillator, and allows
the output driver to switch. If VINdrops below +9.7V,
the UVLO circuit will shut down the CPWM comparator,
ILIM comparator, oscillator, and output driver thereby
returning the MAX16801 to the startup mode.
MAX16801 Startup Operation

In isolated LED driver applications, VINcan be derived
from a tertiary winding of a transformer. However, at
startup there is no energy delivered through the trans-
former. Therefore, a special bootstrap sequence is
required. Figure 3 shows the voltages on IN and VCC
during startup. Initially, both VINand VCCare 0V. After
the line voltage is applied, C1 charges through the
startup resistor R1 to an intermediate voltage. At this
point, the internal regulator begins charging C2 (see
Figure 5). The MAX16801 uses only 45µA of the current
supplied by R1, and the remaining input current
charges C1 and C2. The charging of C2 stops when
the VCCvoltage reaches approximately +9.5V, while
the voltage across C1 continues rising until it reachesVVRINULR
ULR2− VVV
ULRIN
UVLOINULR3500≅×()−
MAX16801A/B/MAX16802A/B
Offline and DC-DC PWM Controllers for
High-Brightness LED Drivers

VDC
(a)
MAX16802A
VDC
(b)
MAX16802A
Figure 2. (a) Resistor-Zener and (b) Transistor-Zener-Resistor Bias Arrangements
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