MAX5068BAUE+T ,High-Frequency, Current-Mode PWM Controller with Accurate Programmable OscillatorELECTRICAL CHARACTERISTICS(V = +12V for the MAX5068B/E/F; V = +23.6V for the MAX5068A/C/D at startu ..
MAX5068EAUE ,10.8 to 24 V, high-frequency, current-mode PWM controller with accurate programmable oscillatorApplications Pin ConfigurationsUniversal-Input AC Power SuppliesTOP VIEWIsolated Telecom Power Supp ..
MAX5069CAUE+ ,High-Frequency, Current-Mode PWM Controller with Accurate Oscillator and Dual FET DriversELECTRICAL CHARACTERISTICS(V = +12V for the MAX5069C/D, V = +23.6V for the MAX5069A/B at startup, t ..
MAX5069CAUE+T ,High-Frequency, Current-Mode PWM Controller with Accurate Oscillator and Dual FET DriversApplicationsUniversal-Input AC Power SuppliesPin ConfigurationIsolated Telecom Power SuppliesNetwor ..
MAX506ACPP ,Quad 8-Bit DACs with Rail-to-Rail Voltage OutputsELECTRICAL CHARACTERISTICS
(VDD = +5V 110%, Vss = 0V to -5.5V, AGND = DGND = 0V, VREF = 4V, RL = ..
MAX506ACPP ,Quad 8-Bit DACs with Rail-to-Rail Voltage OutputsFeatures
. Opennefrom Single +5VS|pplyor Duaieivsupphse
. Output Buffer Amplifiers Swing Rail-to- ..
MAX932CUA ,Ultra Low-Power, Low-Cost Comparators with 2eferenceELECTRICAL CHARACTERISTICS—5V Operation (continued)(V+ = 5V, V- = GND = 0V, T = T to T , unless oth ..
MAX932CUA+ ,Ultra-Low-Power, Low-Cost Comparators with 2% ReferenceMAX931-MAX93419-0194; Rev 1; 2/97Ultra Low -Pow er, Low -CostComparators w ith 2% Reference________ ..
MAX932ESA ,Ultra Low-Power, Low-Cost Comparators with 2eferenceELECTRICAL CHARACTERISTICS—5V Operation (continued)(V+ = 5V, V- = GND = 0V, T = T to T , unless oth ..
MAX932ESA+ ,Ultra-Low-Power, Low-Cost Comparators with 2% ReferenceGeneral Description ________
MAX932ESA+T ,Ultra-Low-Power, Low-Cost Comparators with 2% ReferenceApplications5 HYSTBattery-Powered SystemsThreshold Detectors6 REFMAX931Window ComparatorsV- GND2 1O ..
MAX933CPA ,Ultra Low-Power, Low-Cost Comparators with 2eferenceApplications5 HYSTBattery-Powered SystemsThreshold Detectors6 REFMAX931Window ComparatorsV- GND21Os ..
MAX5068BAUE+T
High-Frequency, Current-Mode PWM Controller with Accurate Programmable Oscillator
General DescriptionThe MAX5068 is a high-frequency, current-mode,
pulse-width modulation (PWM) controller that integrates
all the building blocks necessary for implementing AC-
DC or DC-DC fixed-frequency power supplies. Isolated
or nonisolated power supplies are easily constructed
using either primary- or secondary-side regulation.
Current-mode control with leading-edge blanking sim-
plifies control-loop design, and a programmable inter-
nal slope-compensation circuit stabilizes the current
loop when operating at duty cycles above 50%. The
MAX5068A/B limit the maximum duty cycle to 50% for
use in single-ended forward converters. The
MAX5068C/D/E/F allow duty cycles up to 75%. The
MAX5068 features an accurate externally programma-
ble oscillator that simplifies system design.
An input undervoltage lockout (UVLO) programs the
input-supply startup voltage and ensures proper opera-
tion during brownout conditions.
A single external resistor programs the output switching
frequency from 12.5kHz to 1.25MHz. The MAX5068A/
B/C/E provide a SYNC input for synchronization to an
external clock. The maximum FET-driver duty cycle is
50% for the MAX5068A/B and 75% for the MAX5068C/
D/E/F. Programmable hiccup current limit provides
additional protection under severe faults.
The MAX5068 is specified over the -40°C to +125°C
automotive temperature range and is available in a
16-pin thermally enhanced TSSOP-EP package. Refer to
the MAX5069 data sheet for dual FET-driver applications.
Warning:The MAX5068 is designed to work with high
voltages. Exercise caution.
ApplicationsUniversal-Input AC Power Supplies
Isolated Telecom Power Supplies
Networking System Power Supplies
Server Power Supplies
Industrial Power Conversion
FeaturesCurrent-Mode Control with 47µA (typ) Startup
CurrentResistor-Programmable ±4.5% Accurate
Switching Frequency:
25kHz to 1.25MHz (MAX5068A/B)
12.5kHz to 625kHz (MAX5068C/D/E/F)Rectified 85VACto 265VACor 36VDCto 72VDC
Input (MAX5068A/C/D)Input Directly Driven from 10.8V to 24V
(MAX5068B/E/F)Frequency Synchronization Input
(MAX5068A/B/C/E)Programmable Dead Time and Slope
CompensationProgrammable Startup Voltage (UVLO)Programmable UVLO Hysteresis
(MAX5068A/B/D/F)Integrating Fault Protection (Hiccup)-40°C to +125°C Automotive Temperature Range16-Pin Thermally Enhanced TSSOP-EP Package
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable OscillatorREG5
VCC
NDRV
AGND
PGND
AGND
TOP VIEW
MAX5068A/B
TSSOP-EPSYNC
HYST
UVLO/EN
COMP
FLTINT
Pin Configurations
Ordering Information19-3176; Rev 1; 7/04
*EP = Exposed pad.
PARTTEMP RANGEPIN-PACKAGEMAX5068AAUE-40°C to +125°C16 TSSOP-EP*
MAX5068BAUE-40°C to +125°C16 TSSOP-EP*
MAX5068CAUE-40°C to +125°C16 TSSOP-EP*
MAX5068DAUE-40°C to +125°C16 TSSOP-EP*
MAX5068EAUE-40°C to +125°C16 TSSOP-EP*
MAX5068FAUE-40°C to +125°C16 TSSOP-EP*
Pin Configurations continued at end of data sheet.
Selector Guide appears at end of data sheet.
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; TA= TMINto TMAX, 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 PGND ............................................................-0.3V to +30V
IN to AGND.............................................................-0.3V to +30V
VCCto PGND..........................................................-0.3V to +13V
VCCto AGND..........................................................-0.3V to +13V
FB, COMP, CS, HYST, SYNC, REG5 to AGND........-0.3V to +6V
UVLO/EN, RT, DT, SCOMP, FLTINT to AGND.........-0.3V to +6V
NDRV to PGND...........................................-0.3V to (VCC+ 0.3V)
AGND to PGND.....................................................-0.3V to +0.3V
Continuous Power Dissipation
16-Pin TSSOP-EP (derate 21.3mW/°C above +70°C)...1702mW
Operating Temperature Range..........................-40°C to +125°C
Maximum Junction Temperature.....................................+150°C
Storage Temperature Range.............................-60°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
UNDERVOLTAGE LOCKOUT/STARTUP
Bootstrap UVLO Wake-Up LevelVSUVRVIN rising, MAX5068A/C/D only19.6821.623.60V
Bootstrap UVLO Shutdown LevelVSUVFVIN falling, MAX5068A/C/D only9.059.7410.43V
UVLO/EN Wake-Up ThresholdVULR2VUVLO/EN rising1.2051.2301.255V
UVLO/EN Shutdown ThresholdVULF2VUVLO/EN falling1.18V
HYST FET On-ResistanceRD S ( ON ) _H MAX5068A/B/D/F only, sinking 50mA,
VUVLO/EN = 0V10Ω
HYST FET Leakage CurrentILEAK_HVUVLO/EN = 2V, VHYST = 5V3nA
IN Supply Current In
Undervoltage LockoutISTARTVIN = +19V, VUVLO/EN < VULF24790µA
IN RangeVIN10.824.0V
INTERNAL SUPPLIES (VCC and REG5)
VCC Regulator Set PointVCCSPV IN = + 10.8V to + 24V , V C C sour ci ng 1µA to 25m A7.010.5V
REG5 Output VoltageVREG5IREG5 = 0 to 1mA4.855.005.15V
REG5 Short-Circuit Current LimitIREG5_SC18mA
fSW = 1.25MHz5IN Supply Current After StartupIINVIN = +24VfSW = 100kHz2.5mA
Shutdown Supply CurrentIIN_SD90µA
GATE DRIVER (NDRV)
ZOUT(LOW)NDRV sinking 100mA24Driver Output ImpedanceZOUT(HIGH)NDRV sourcing 25mA36Ω
Sinking1000Driver Peak Output CurrentINDRVSourcing650mA
PWM COMPARATOR
Comparator Offset VoltageVOS_PWMVCOMP - VCS1.301.602.00V
Comparator Propagation DelaytPD_PWMVCS = 0.1V40ns
Minimum On-TimetON(MIN)Includes tCS_BLANK110ns
CURRENT-LIMIT COMPARATOR
Current-Limit Trip ThresholdVCS298314330mV
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
CS Input Bias CurrentIB_CSVCS = 0V0+2µA
CS Blanking TimetCS_BLANK70ns
Propagation Delay from
Comparator Input to NDRV50mV overdrive40ns
IN CLAMP VOLTAGE
IN Clamp VoltageVIN_CLAMPVIN sinking 2mA (Note 2)24.026.029.0V
ERROR AMPLIFIER (FB, COMP)
Voltage GainAVRCOMP = 100kΩ to AGND80dB
Unity-Gain BandwidthBWRCOMP = 100kΩ to AGND,
CLOAD = 100pF to AGND5MHz
Phase MarginPMRCOMP = 100kΩ to AGND,
CLOAD = 100pF to AGND65degrees
FB Input Offset VoltageVOS_FB3mV
High2.63.8COMP Clamp VoltageVCOMPLow0.41.1V
Error-Amplifier Output CurrentICOMPSinking or sourcing0.5mA
+25°C ≤ TA ≤ +125°C (Note 3)1.2151.2301.245
Reference VoltageVREF-40°C ≤ TA ≤ +125°C1.2051.2301.242V
Input Bias CurrentIB_EA100300nA
COMP Short-Circuit CurrentICOMP_SC12mA
THERMAL SHUTDOWN
Thermal-Shutdown TemperatureTSD+170°C
Thermal HysteresisTHYST+25°C
OSCILLATOR SYNC INPUT (MAX5068A/B/C/E Only)
SYNC High-Level VoltageVIH_SYNC2.4V
SYNC Low-Level VoltageVIL_SYNC0.4V
SYNC Input Bias CurrentIB_SYNC10nA
Maximum SYNC FrequencyfSYNCfOSC = 2.5MHz (Note 4)3.125MHz
SYNC High-Level Pulse WidthtSYNC_HI30ns
SYNC Low-Level Pulse WidthtSYNC_LO30ns
DIGITAL SOFT-START
Soft-Start DurationtSS(Note 5)2047cycles
Reference-Voltage StepVSTEP9.7mV
Reference-Voltage Steps During
Soft-Start127steps
OSCILLATOR
Internal Oscillator Frequency
RangefOSCfOSC = (1011 / RRT)502500kHz
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
Note 1:The MAX5068 is 100% tested at TA= +25°C. All limits over temperature are guaranteed by design.
Note 2:The MAX5068A/B are intended for use in universal-input power supplies. The internal clamp circuit is used to prevent the
bootstrap capacitor (C1 in Figure1) from charging to a voltage beyond the absolute maximum rating of the device when
UVLO/EN is low. The maximum current to VIN(hence to clamp) when UVLO is low (device is in shutdown) must be external-
ly limited to 2mA. Clamp currents higher than 2mA may result in clamp voltages higher than 30V, thus exceeding the
absolute maximum rating for VIN. For the MAX5068C/D, do not exceed the 24V maximum operating voltage of the device.
Note 3:Reference voltage (VREF) is measured with FB connected to COMP (see the Functional Diagram).
Note 4:The SYNC frequency must be at least 25% higher than the programmed oscillator frequency.
Note 5:The internal oscillator clock cycle.
Note 6:The MAX5068A/B driver switching frequency is one-half of the oscillator frequency. The MAX5068C/D/E/F driver switching
frequency is one-quarter of the oscillator frequency.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
fSW = 1011/(2 x RRT),
MAX5068A/B251250kHz
NDRV Switching FrequencyfSW(Note 6)
fSW = 1011/(4 x RRT),
MAX5068C/D/E/F12.5625kHz
RT VoltageVRT40kΩ < RRT < 500kΩ2.0V
fOSC ≤ 500kHz-2.5+2.5TA = +25°CfOSC > 500kHz-4+4
fOSC ≤ 500kHz-4.5+4.5Oscillator Accuracy
TA = - 40° C to + 125° C fOSC > 500kHz-6+6
MAX5068A/B50Maximum Duty CycleDMAXDT connected to
REG5MAX5068C/D/E/F75%
DEAD-TIME CONTROL (DT)
Dead TimetDTRDT = 24.9kΩ60ns
Dead-Time Disable VoltageV D T_D IS ABLE VREG5
- 0.5VV
Dead-Time Regulation VoltageVDT1.23V
INTEGRATING FAULT PROTECTION (FLTINT)
FLTINT Source CurrentIFLTINTVFLTINT = 060µA
FLTINT Shutdown ThresholdVFLTINT_SDVFLTINT rising2.8V
FLTINT Restart ThresholdVFLTINT_RSVFLTINT falling1.6V
SLOPE COMPENSATION (SCOMP) MAX5068C/D/E/F Only
Slope CompensationVSLOPECSLOPE = 100pF, RRT = 110kΩ15mV/µs
Slope-Compensation RangeVSLOPER090mV/µs
Slope-Compensation Voltage
RangeVSCOMP02.7V
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
MAX5068 toc01
TEMPERATURE (°C)
(V)603510-15
MAX5068A/C/D
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
MAX5068 toc02
TEMPERATURE (°C)
(V)603510-15
VIN FALLING
MAX5068A/C/D
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
MAX5068 toc03
TEMPERATURE (°C)
UVLO/EN (V)603510-15
UVLO/EN RISING
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
MAX5068 toc04
TEMPERATURE (°C)
UVLO/EN (V)603510-15
UVLO/EN FALLING
VIN SUPPLY CURRENT IN
UNDERVOLTAGE LOCKOUT vs. TEMPERATURE
MAX5068 toc05
TEMPERATURE (°C)
ISTART603510-15
VIN = 19V
WHEN IN BOOTSTRAP UVLO (MAX5068A/C/D)
UVLO/EN (MAX5068B/E/F) IS LOW
VIN SUPPLY CURRENT AFTER STARTUP
vs. TEMPERATURE
MAX5068 toc06
TEMPERATURE (°C)
IIN
(mA)603510-15
VIN = 24V
fSW = 1.25MHz
fSW = 500kHz
fSW = 250kHz
fSW = 100kHz
fSW = 50kHz
VCC vs. TEMPERATURE
MAX5068 toc07
TEMPERATURE (°C)
(V)603510-15
VIN = 19V, IIN = 25mA
VIN = 19V, IIN = 10mA
VIN = 10.8V, IIN = 10mA
VIN = 10.8V, IIN = 25mA
REG5 OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX5068 toc08
OUTPUT CURRENT (mA)
REG5 (V)
RRT = 100kΩ
REG5 vs. TEMPERATURE
MAX5068 toc09
TEMPERATURE (°C)
REG5 (V)603510-15
VIN = 10.8V
100μA LOAD
1mA LOAD
Typical Operating Characteristics
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; VFB= 0; VCOMP= floating; VCS= 0; TA= +25°C, unless otherwise noted.)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
Typical Operating Characteristics (continued)
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; VFB= 0; VCOMP= floating; VCS= 0; TA= +25°C, unless otherwise noted.)
REG5 OUTPUT VOLTAGE vs. VIN
MAX5068 toc10
VIN (V)
REG5 (V)20161814121024
IREG5 = 100μA
CS TRIP THRESHOLD
vs. TEMPERATURE
MAX5068 toc11
TEMPERATURE (°C)
CS TRIP THRESHOLD (mV)
SWITCHING FREQUENCY
vs. TEMPERATUREMAX5068 toc12
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
fSW = 500kHzTOTAL NUMBER OF
DEVICES = 200
MEAN
-3σ
+3σ
PROPAGATION DELAY FROM CS COMPARATOR
INPUT TO NDRV vs. TEMPERATUREMAX5068 toc13
TEMPERATURE (°C)
PROPAGATION DELAY (ns)
INPUT CURRENT
vs. INPUT CLAMP VOLTAGE
MAX5068 toc14
INPUT CLAMP VOLTAGE (V)
INPUT CURRENT (mA)
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
MAX5068 toc15
TEMPERATURE (°C)
INPUT CLAMP VOLTAGE (V)
ISINK = 2mA
NDRV OUTPUT IMPEDANCE
vs. TEMPERATUREMAX5068 toc16
TEMPERATURE (°C)603510-15
VIN = 24V
SINKING 100mA
NDRV OUTPUT IMPEDANCE
vs. TEMPERATUREMAX5068 toc17
TEMPERATURE (°C)603510-15
VIN = 24V
SOURCING 25mA
ERROR AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCYMAX5068 toc18
FREQUENCY (Hz)
GAIN (dB)
PHASE (DEGREES)
10M10100k1k
GAIN
PHASE
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
FLTINT CURRENT vs. TEMPERATUREMAX5068 toc19
TEMPERATURE (°C)
FLTINT CURRENT (603510-15
HYST RON vs. TEMPERATURE
MAX5068 toc20
TEMPERATURE (°C)603510-15
VIN = 24V
SINKING 50mA
NDRV SWITCHING FREQUENCY (fSW)
vs. RRTMAX5068 toc21
RRT (MΩ)
(MHz)
MAX5068A/B
MAX5068C/D/E/F
NDRV SWITCHING FREQUENCY
vs. TEMPERATUREMAX5068 toc22
TEMPERATURE (°C)
NDRV SWITCHING FREQUENCY (kHz)
fSW = 50kHz
NDRV SWITCHING FREQUENCY
vs. TEMPERATUREMAX5068 toc23
TEMPERATURE (°C)
NDRV SWITCHING FREQUENCY (kHz)
fSW = 500kHz
NDRV SWITCHING FREQUENCY
vs. TEMPERATUREMAX5068 toc24
TEMPERATURE (°C)
NDRV SWITCHING FREQUENCY (kHz)
MAX5068A/B
fSW = 1.25MHz
DEAD TIME vs. TEMPERATUREMAX5068 toc25
TEMPERATURE (°C)
TIME (ns)
VIN = 24V
RDT = 24.9kΩ
RRT = 100kΩ
DEAD TIME vs. RDTMAX5068 toc26
RDT (kΩ)
TIME (ns)
Typical Operating Characteristics (continued)
(VIN = +12V for the MAX5068B/E/F; VIN= +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN= CREG5= 0.1µF;
CVCC= 1µF; RRT= 100kΩ; NDRV = floating; VFB= 0; VCOMP= floating; VCS= 0; TA= +25°C, unless otherwise noted.)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
Pin Description
PIN
MAX5068A
MAX5068B
MAX5068C
MAX5068E
MAX5068D
MAX5068F
NAMEFUNCTION111RTOscillator-Timing Resistor Connection. Connect a resistor from RT to AGND
to set the internal oscillator frequency.2—SYNCExternal-Clock Sync Input. Connect SYNC to AGND when not using an
external clock.—2HYSTProgrammable Hysteresis Input3SCOMPSlope-Compensation Capacitor Input. Connect a capacitor to AGND to set
the slope compensation.
444DTDead-Time Adjustment. Connect a resistor from DT to AGND to adjust NDRV
dead time. Connect to REG5 for maximum duty cycle.
555UVLO/ENExternally Programmable Undervoltage Lockout. UVLO/EN programs the
input start voltage. Drive UVLO/EN to AGND to disable the output.66FBError-Amplifier Inverting Input77COMPError-Amplifier Compensation Output
888FLTINT
Fault-Integration Input. A capacitor connected to FLTINT charges with an
internal 60µA current source during repeated current-limit events. Switching
terminates when VFLTINT reaches 2.9V. An external resistor connected in
parallel discharges the capacitor. Switching resumes when VFLTINT drops to
1.6V.99CSCurrent-Sense Resistor Connection
10, 1210, 1210, 12AGNDAnalog Ground. Connect to PGND through a ground plane.1111PGNDPower Ground. Connect to AGND through a ground plane. 13 13NDRVG ate- D r i ver O utp ut. C onnect the N D RV outp ut to the g ate of the exter nal - channel FE T.1414VCC9V Linear-Regulator Output. Decouple VCC with a minimum 1µF ceramic
capacitor to the AGND plane; also internally connected to the FET driver.1515IN
Power-Supply Input. IN provides power for all internal circuitry. Decouple IN
with a minimum 0.1µF ceramic capacitor to AGND (see the Typical
Operating Circuit).1616REG55V Linear-Regulator Output. Decouple to AGND with a 0.1µF ceramic
capacitor.EPEPPADExposed Pad. Connect to GND.
Detailed DescriptionThe MAX5068 is a current-mode PWM controller for use
in isolated and nonisolated power-supply applications.
A bootstrap UVLO with a programmable hysteresis,
very low startup, and low operating current result in
high-efficiency universal-input power supplies. In addi-
tion to the internal bootstrap UVLO, the device also
offers programmable input startup and turn-off volt-
ages, programmed through the UVLO/EN input. When
using the MAX5068 in the bootstrapped mode, if the
power-supply output is shorted, the tertiary winding
voltage drops below the 10V threshold, causing the
bootstrap UVLO to turn off the gate drive to the external
power MOSFET, reinitiating a startup sequence with
soft-start.
The MAX5068 includes a cycle-by-cycle current limit
that turns off the gate drive to the external MOSFET
during an overcurrent condition. The MAX5068 integrat-
ing fault protection reduces average power dissipation
during persistent fault conditions (see the Integrating
Fault Protectionsection).
The MAX5068 features a very accurate, wide-range,
programmable oscillator that simplifies and optimizes
the design of the magnetics. The MAX5068A/C/D are
well suited for universal-input (rectified 85VACto
265VAC) or telecom (-36VDCto -72VDC) power sup-
plies. The MAX5068B/E/F are well suited for low-input
voltage (10.8VDCto 24VDC) power supplies.
The MAX5068 high-frequency, universal input, offline/
telecom, current-mode PWM controller integrates all the
building blocks necessary for implementing AC-DC and
DC-DC fixed-frequency power supplies. Isolated or non-
isolated power supplies are easily constructed using
either primary- or secondary-side regulation. Current-
mode control with leading-edge blanking simplifies con-
trol-loop design, and an external slope-compensation
control stabilizes the current loop when operating at
duty cycles above 50% (MAX5068C/D/E/F). The
MAX5068A/B limit the maximum duty cycle to 50% for
use in single-ended forward converters. The
MAX5068C/D/E/F allow duty cycles up to 75% for use in
flyback converters.
An input undervoltage lockout (UVLO) programs the
input-supply startup voltage and ensures proper opera-
tion during brownout conditions. An external voltage-
divider programs the supply startup voltage. The
MAX5068A/B/D/F feature a programmable UVLO hys-
teresis. The MAX5068A/C/D feature an additional internal
bootstrap UVLO with large hysteresis that requires a min-
imum startup voltage of 23.6V. The MAX5068B/E/F start
up from a minimum voltage of 10.8V. Internal digital soft-
start reduces output-voltage overshoot at startup.
A single external resistor programs the switching fre-
quency from 12.5kHz to 1.25MHz. The MAX5068A/B/C/E
provide a SYNC input for synchronization to an external
clock. The maximum FET driver duty cycle is 50% for the
MAX5068A/B, and 75% for the MAX5068C/D/E/F.
Integrating fault protection ignores transient overcurrent
conditions for a set length of time. The length of time is
programmed by an external capacitor. The internal ther-
mal-shutdown circuit protects the device if the junction
temperature should exceed +170°C.
Power supplies designed with the MAX5068 use a
high-value startup resistor, R1, which charges a reser-
voir capacitor, C1 (Figure1). During this initial period,
while the voltage is less than the internal bootstrap
UVLO threshold, the device typically consumes only
47µA of quiescent current. This low startup current and
the large bootstrap UVLO hysteresis help to minimize
the power dissipation across R1, even at the high end
of the universal AC input voltage (265VAC).
The MAX5068 includes a cycle-by-cycle current limit
that turns off the gate to the external MOSFET during an
overcurrent condition. When using the MAX5068A/C/D
in the bootstrap mode (if the power-supply output is
shorted), the tertiary winding voltage drops below the
9.74V bootstrap UVLO to turn off the gate to the exter-
nal power MOSFET. This reinitiates a startup sequence
with soft-start.
Current-Mode ControlThe MAX5068 offers a current-mode control operation
feature, such as leading-edge blanking with a dual
internal path that only blanks the sensed current signal
applied to the input of the PWM controller. The current-
limit comparator monitors CS at all times and provides
cycle-by-cycle current limit without being blanked. The
leading-edge blanking of the CS signal prevents the
PWM comparator from prematurely terminating the on
cycle. The CS 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. Since this leading-edge spike is nor-
mally lower than the current-limit comparator threshold,
current limiting is provided under all conditions.
Use the MAX5068C/D/E/F in flyback applications where
wide line voltage and load-current variations are
expected. Use the MAX5068A/B for forward/flyback
converters where the maximum duty must be limited to
less than 50%.
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
MAX5068Use the MAX5068C/D/E/F in forward converter applica-
tions with greater than 50% duty cycle. The large duty
cycle results in much lower operating primary RMS cur-
rent through the MOSFET switch and, in most cases,
requires a smaller output filter capacitor. The major dis-
advantage to this is that the MOSFET voltage rating
must be higher. The MAX5068C/D/E/F capacitor
adjustable-slope-compensation feature allows for easy
stabilization of the inner current loop.
Undervoltage LockoutThe MAX5068 features an input voltage UVLO/EN func-
tion to enable the PWM controller before any operation
can begin. The MAX5068C/E shut down if the voltage
at UVLO/EN falls below its 1.18V threshold. The
MAX5068A/B/D/F also incorporate an UVLO hysteresis
input to set the desired turn-off voltage.
MAX5068C/E UVLO AdjustmentThe MAX5068C/E have an input voltage UVLO/EN with
a 1.231V threshold. Before any operation can com-
mence, the UVLO/EN voltage must exceed the 1.231V
threshold. The UVLO circuit keeps the PWM compara-
tor, ILIM comparator, oscillator, and output driver shut
down to reduce current consumption (see the
Functional Diagram).
Calculate R6 in Figure2 by using the following formula:
where VULR2is the UVLO/EN’s 1.231V rising threshold
and VONis the desired startup voltage. Choose an R7
value in the 20kΩrange.
After a successful startup, the MAX5068C/E shut down if
the voltage at UVLO/EN drops below its 1.18V threshold.VRON
ULR7 =⎛⎜⎞⎟×−
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable OscillatorMAX5068A
NDRV
PGNDVCC
AGND
REG5
UVLO/EN
HYST
FLTINTC1
COMP
VIN
RHYST
SYNCC5
RCS
VOUTD1
Figure1. Nonisolated Power Supply with Programmable Input Supply Voltage
