MAX15001AEUB+T ,Current-Mode PWM Controllers with Programmable Switching FrequencyFeatures♦ Current-Mode ControlThe MAX15000/MAX15001 current-mode PWM con-trollers contain all the c ..
MAX15005BAUE+ ,4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply ControllersFeaturesThe MAX15004A/B/MAX15005A/B high-performance, ● Wide Supply Voltage Range Meets Automotive ..
MAX15006AASA+T ,40V, Ultra-Low Quiescent-Current Linear Regulators in 6-Pin TDFN/8-Pin SOElectrical Characteristics(V = 14V, I = 1mA, C = 0.1μF, C = 2.2μF, T = T = -40°C to +125°C, unless ..
MAX15006AATT+ ,40V, Ultra-Low Quiescent-Current Linear Regulators in 6-Pin TDFN/8-Pin SOFeatures● Wide Operating Input Voltage Range (4V to 40V)The MAX15006/MAX15007 ultra-low quiescent-c ..
MAX15006BASA+T ,40V, Ultra-Low Quiescent-Current Linear Regulators in 6-Pin TDFN/8-Pin SOApplicationsPART TEMP RANGEPACKAGE MARK● AutomotiveMAX15006AASA+ -40°C to +125°C 8 SO-EP* —● Tire-P ..
MAX15006BATT+ ,40V, Ultra-Low Quiescent-Current Linear Regulators in 6-Pin TDFN/8-Pin SOElectrical Characteristics(V = 14V, I = 1mA, C = 0.1μF, C = 2.2μF, T = T = -40°C to +125°C, unless ..
MAX4124EUK-T ,Single/Dual/Quad, Wide-Bandwidth, Low-Power, Single-Supply Rail-to-Rail I/O Op AmpsELECTRICAL CHARACTERISTICS (continued)(V = +2.7V to +6.5V, V = 0V, V = 0V, V = V /2, R tied to V /2 ..
MAX4125ESA ,Single, wide-bandwidth, low-power, single-supply Rail-to-Rail I/O op amp. BW 25MHz.ApplicationsMAX4123C/D 0°C to +70°C Dice* —Battery-Powered InstrumentsMAX4123ESA -40°C to +85°C 8 S ..
MAX4125ESA+ ,Single/Dual/Quad, Wide-Bandwidth, Low-Power, Single-Supply Rail-to-Rail I/O Op AmpsApplications Pin Configurations appear at end of data sheet.__________Typical Operating CircuitSele ..
MAX4126 ,Single/Dual/Quad, Wide-Bandwidth, Low-Power, Single-Supply Rail-to-Rail I/O Op AmpsFeaturesThe MAX4122–MAX4129 family of operational amplifiers♦ 5-Pin SOT23 Package (MAX4122/4)combin ..
MAX4126ESA ,Dual, wide-bandwidth, low-power, single-supply Rail-to-Rail I/O op amp. BW 5MHz.Applications Pin Configurations appear at end of data sheet.__________Typical Operating CircuitSele ..
MAX4126ESA ,Dual, wide-bandwidth, low-power, single-supply Rail-to-Rail I/O op amp. BW 5MHz.FeaturesThe MAX4122–MAX4129 family of operational amplifiers' 5-Pin SOT23 Package (MAX4122/4)combin ..
MAX15001AEUB+T
Current-Mode PWM Controllers with Programmable Switching Frequency
General DescriptionThe MAX15000/MAX15001 current-mode PWM con-
trollers contain all the control circuitry required for the
design of wide-input-voltage isolated and nonisolated
power supplies. The MAX15000 is well suited for uni-
versal input (rectified 85VAC to 265VAC) or telecom
(-36VDC to -72VDC) power supplies. The MAX15001
is well suited for low input voltage (9.5VDC to 24VDC)
power supplies.
The MAX15000/MAX15001 contain an internal error
amplifier that regulates the tertiary winding output volt-
age which is used in primary-side-regulated isolated
power supplies. Primary-side regulation eliminates the
need for an optocoupler. An input undervoltage lockout
(UVLO) is provided for programming the input-supply
start voltage and to ensure proper operation during
brownout conditions. An open-drain UVLO flag output,
with 210µs internal delay, allows the sequencing of a
secondary-side controller. The input-supply start volt-
age is externally programmable with a voltage-divider.
A UVLO/EN input is used to shutdown the MAX15000/
MAX15001. Internal digital soft-start eliminates output
voltage overshoot.
The MAX15000 has an internal bootstrap UVLO with
large hysteresis that requires a minimum 23.6V for start-
up. The MAX15001 does not have the internal bootstrap
UVLO and can be biased directly from a minimum volt-
age of 9.5V.
The switching frequency for the MAX15000/MAX15001 is
programmable with an external resistor. The MAX15000A/
MAX15001A provide a 50% maximum duty-cycle limit,
while the MAX15000B/MAX15001B provide a 75% maxi-
mum duty-cycle limit. These devices are available in 10-
pin µMAX®packages and are rated for operation over the
-40°C to +85°C temperature range.
Applications1/2, 1/4, and 1/8th Brick Power Modules
High-Efficiency, Isolated Telecom Power
Supplies
Networking/Servers
Isolated Keep-Alive Power Supplies
12V Boost and SEPIC Regulators
Isolated and Nonisolated High-Brightness LED
Power Supplies
Industrial Power Conversion
FeaturesCurrent-Mode ControlProgrammable Switching Frequency Up to 625kHzAccurate UVLO Threshold (1%)Open-Drain UVLO Flag Output with Internal Delay36V to 72V Telecom Voltage RangeUniversal Offline Input Voltage Range
Rectified 85VAC to 265VAC (MAX15000)9.5V to 24V Input (MAX15001)Digital Soft-StartInternal Bootstrap UVLO with Large Hysteresis
(MAX15000)Internal Error Amplifier with 1.5% Accurate
Reference50µA (typ) Startup Supply Current50% Maximum Duty-Cycle Limit
(MAX15000A/MAX15001A)75% Maximum Duty-Cycle Limit
(MAX15000B/MAX15001B)60ns Cycle-by-Cycle Current-Limit Propagation
DelayAvailable in Tiny 10-Pin µMAX Packages
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching FrequencyVCC
NDRV
GNDCOMP
UFLG
UVLO/EN
MAX15000
MAX15001
µMAX
TOP VIEWCS
Pin Configuration
Ordering Information19-3957; Rev 0; 1/06
Warning:The MAX15000/MAX15001 are designed to work with
high voltages. Exercise caution.
+Denotes lead-free package.
EVALUATION KIT
AVAILABLE
Selector Guide appears at end of data sheet.
PARTTEMP RANGEPIN-
PACKAGE
PKG
CODE
MAX15000AEUB+-40°C to +85°C10 µMAXU10-2
MAX15000BEUB+-40°C to +85°C10 µMAXU10-2
MAX15001AEUB+-40°C to +85°C10 µMAXU10-2
MAX15001BEUB+-40°C to +85°C10 µMAXU10-2
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= +12V (for MAX15000, bring VINup to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX1500_A), R12
= 7.5kΩ(MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN= +1.4V, VFB= +1.0V,
COMP = open, 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
IN Clamp (Internal Shunt) Current........................................5mA
VCCto GND............................................................-0.3V to +13V
FB, COMP, UVLO/EN, RT, CS to GND.....................-0.3V to +6V
UFLG to GND.........................................................-0.3V to +30V
NDRV to GND............................................-0.3V to (VCC+ 0.3V)
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C)........444.4mW
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
UVLO/STARTUPBootstrap UVLO Wake-Up LevelVSUVRVIN rising (MAX15000 only)19.6821.623.60V
Bootstrap UVLO Shutdown LevelVSUVFVIN falling (MAX15000 only)9.059.7410.43V
UVLO/EN Wake-Up ThresholdVULR2UVLO/EN rising1.2181.231.242V
UVLO/EN Shutdown ThresholdVULF2UVLO/EN falling1.141.171.20V
UVLO/EN Input CurrentIUVLOVUVLO/EN ≤ 2V-50+50nA
UVLO/EN Hysteresis60mV
IN Supply Current In UVLOISTARTVIN = 19V, MAX15000 only when in
bootstrap UVLO5090µA
IN Input Voltage RangeVINMAX15001 only9.524.0V
UVLO/EN steps up from 1V to 1.4V3UVLO/EN to UFLG Propagation
Delay (Figure 3)UVLO/EN steps down from 1.4V to 1V0.6µs
tEXTRUVLO/EN steps up from 1V to 1.4V310msUVLO/EN to NDRV Propagation
Delay (Figure 3)tEXTFUVLO/EN steps down from 1.4V to 1V150210300µs
tBUVRVIN steps up from 9V to 24V (MAX15000
only)5
Bootstrap UVLO Propagation
DelaytBUVFVIN steps down from 24V to 9V
(MAX15000 only)1
UFLG Low Output VoltageVUFLGIUFLG = 5mA sinking0.8V
UFLG High Output Leakage
CurrentVUFLG = 25V0.11µA
INTERNAL SUPPLYVCC Regulator Set PointVCCSPVIN = 10.8V to 24V, sinking 1µA to 20mA
from VCC7.010.5V
IN Supply Current After StartupIINVIN = 24V24mA
Shutdown Supply CurrentUVLO/EN = low5090µA
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
ELECTRICAL CHARACTERISTICS (continued)(VIN= +12V (for MAX15000, bring VINup to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX1500_A), R12
= 7.5kΩ(MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN= +1.4V, VFB= +1.0V,
COMP = open, VCS= 0V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GATE DRIVERRON(LOW)Measured at NDRV sinking 100mA24Driver Output ImpedanceRON(HIGH)Measured at NDRV sourcing 20mA410Ω
Driver Peak Sink Current1A
Driver Peak Source Current0.65A
PWM COMPARATORComparator Offset VoltageVPWMVCOMP - VCS1.241.381.54V
CS Input Bias CurrentICSVCS = 0V-4+4µA
Comparator Propagation DelaytPWMChange in VCS = 0.1V60ns
CURRENT-LIMIT COMPARATORCurrent-Limit Trip ThresholdVCS90010001100mV
CS Input Bias CurrentICSVCS = 0V-4+4µA
Propagation Delay From
Comparator Input to NDRVtPDCS100mV overdrive60ns
IN CLAMP VOLTAGEIN Clamp VoltageVINC2mA sink current (Note 2)24.126.129.0V
ERROR AMPLIFIERVoltage GainRLOAD = 100kΩ80dB
Unity-Gain BandwidthRLOAD = 100kΩ, CLOAD = 200pF2MHz
Phase MarginRLOAD = 100kΩ, CLOAD = 200pF65degrees
FB Input Offset Voltage±1mV
COMP High VoltageICOMP = 02.8
COMP Low VoltageICOMP = 01.1V
Source Current0.5mA
Sink Current0.5mA
Reference VoltageVREF(Note 3)1.230V
Reference Voltage Accuracy-1.5+1.5%
FB Input Bias Current-50+50nA
COMP Short-Circuit Current8mA
DIGITAL SOFT-START1984NDRV
cyclesSoft-Start DurationtSS
fSW = 350kHz5.6ms
Reference Voltage Steps During
Soft-Start31steps
Reference Voltage Step39.67mV
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
Note 1:All devices are 100% tested at TA= +85°C. All limits over temperature are guaranteed by characterization.
Note 2:The MAX15000 is intended for use in universal input power supplies. The internal clamp circuit at IN 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 (shutdown mode). Externally limit the maximum current to IN (hence to clamp) to 2mA maximum when
UVLO/EN is low. Clamp currents higher than 2mA may result in a clamp voltage higher than 30V, thus exceeding the
absolute maximum rating for IN. For the MAX15001, do not exceed the 24V maximum operating voltage of the device.
Note 3:VREFis measured with FB connected to COMP (see the Functional Diagram).
Note 4:The oscillator in the MAX1500_A is capable of operating up to 2500kHz. However, the NDRV switching frequency is limited
to operate up to 625kHz. Thus, the oscillator frequency for MAX1500_A must be limited to 1250kHz (maximum).
ELECTRICAL CHARACTERISTICS (continued)(VIN= +12V (for MAX15000, bring VINup to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX1500_A), R12
= 7.5kΩ(MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN= +1.4V, VFB= +1.0V,
COMP = open, VCS= 0V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATUREMAX15000 toc01
TEMPERATURE (°C)
(V)3510-15
MAX15000 VIN RISING
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATUREMAX15000 toc02
TEMPERATURE (°C)
(V)3510-15
MAX15000 VIN FALLING
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATUREMAX15000 toc03
TEMPERATURE (°C)
UVLO/EN (V)3510-15
UVLO/EN RISING
Typical Operating Characteristics(VUVLO/EN= +1.4V, VFB= +1V, COMP = open, VCS= 0V, TA= +25°C, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
OSCILLATOROscillator Frequency RangefOSC502500kHz
fOSC = 200kHz to 800kHz-10+10Oscillator Frequency AccuracyfOSC = 50kHz to 2500kHz-20+20%
MAX1500_A, fSW = fOSC/225625NDRV Switching Frequency
(Note 4)fSWMAX1500_B, fSW = fOSC/412.5625.0kHz
MAX1500_A50Maximum Duty CycleDMAXMAX1500_B75%
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATUREMAX15000 toc04
TEMPERATURE (°C)
UVLO/EN
(V)3510-15
UVLO/EN FALLING
VIN SUPPLY CURRENT IN UVLO
vs. TEMPERATUREMAX15000 toc05
TEMPERATURE (°C)
ISTART3510-15
VIN = 19V
MAX15000 WHEN IN
BOOTSTRAP UVLO
VIN SUPPLY CURRENT AFTER
STARTUP vs. TEMPERATUREMAX15000 toc06
TEMPERATURE (°C)
IIN
(mA)3510-15
VIN = 24V
fSW = 350kHz
VCC REGULATOR SET POINT
vs. TEMPERATUREMAX15000 toc07
TEMPERATURE (°C)
(V)3510-15
VIN = 19V
NDRV NOT SWITCHING
NDRV SWITCHING
fSW = 350kHz
VCC REGULATOR SET POINT
vs. TEMPERATUREMAX15000 toc08
TEMPERATURE (°C)
(V)40-20020
10mA LOAD
VIN = 19V
20mA LOAD
CURRENT-LIMIT TRIP THRESHOLD
vs. TEMPERATUREMAX15000 toc09
TEMPERATURE (°C)
CURRENT-LIMIT TRIP THRESHOLD (V)3510-15
-3σ
MEAN
+3σ
TOTAL NUMBER OF DEVICES = 140
CURRENT-LIMIT TRIP THRESHOLDMAX15000 toc10
CURRENT-LIMIT TRIP THRESHOLD (V)
PERCENTAGE OF UNITS (%)
TOTAL NUMBER
OF DEVICES = 140
SWITCHING FREQUENCY
vs. TEMPERATUREMAX15000 toc11
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)3510-15
-3σ
MEAN
+3σ
TOTAL NUMBER OF DEVICES = 140
SWITCHING FREQUENCYMAX15000 toc12
SWITCHING FREQUENCY (kHz)
PERCENTAGE OF UNITS (%)
TOTAL NUMBER
OF DEVICES = 140
Typical Operating Characteristics (continued)(VUVLO/EN= +1.4V, VFB= +1V, COMP = open, VCS= 0V, TA= +25°C, unless otherwise noted.)
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
SWITCHING FREQUENCY
vs. TIMING RESISTORMAX15000 toc13
TIMING RESISTOR (kΩ)
SWITCHING FREQUENCY (kHz)
MAX15000A
PROPAGATION DELAY FROM
CURRENT-LIMIT COMPARATOR
INPUT TO NDRV vs. TEMPERATUREMAX15000 toc14
TEMPERATURE (°C)
tPDCS
(ns)3510-15
UVLO/EN TO NDRV PROPAGATION DELAY
vs. TEMPERATURE
MAX15000 toc15
TEMPERATURE (°C)
UVLO DELAY (ms)3510-15
UVLO/EN RISING
UVLO/EN FALLING206µs
UVLO/EN TO UFLG PROPAGATION DELAY
vs. TEMPERATUREMAX15000 toc16
TEMPERATURE (°C)
UVLO DELAY (3510-15
UVLO/EN RISING
UVLO/EN FALLING
REFERENCE VOLTAGE
vs. TEMPERATUREMAX15000 toc17
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)3510-15
VIN = 12V
INPUT CURRENT
vs. IN VOLTAGEMAX15000 toc18
IN VOLTAGE (V)
INPUT CURRENT (mA)17161514131211
UVLO/EN = 1.4V
NDRV SWITCHING AT 350kHz
INPUT CLAMP VOLTAGE
vs. TEMPERATUREMAX15000 toc19
INPUT CLAMP VOLTAGE (V)40200-20
IIN = 2mA
NDRV LOW OUTPUT IMPEDANCE
vs. TEMPERATUREMAX15000 toc203510-15
VIN = 24V
SINKING 100mA
Typical Operating Characteristics (continued)(VUVLO/EN= +1.4V, VFB= +1V, COMP = open, VCS= 0V, TA= +25°C, unless otherwise noted.)
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
Pin Description
PINNAMEFUNCTIONUVLO/EN
Externally Programmable Undervoltage Lockout. UVLO/EN programs the input start voltage. Connect
UVLO/EN to GND to disable the device. NDRV stops switching approximately 210µs after the UVLO/EN
voltage falls below 1.17V.UFLGOpen-Drain Undervoltage Flag Output. UFLG is asserted low as soon as the UVLO/EN voltage falls below its
threshold.FBError-Amplifier Inverting InputCOMPError-Amplifier Output
5CS
Current-Sense Input. Current-sense connection for PWM regulation and cycle-by-cycle current limit.
Connect to the high side of the sense resistor. An RC filter may be necessary to eliminate leading-edge
spikes. Current-limit trip voltage is 1V.
6RTOscillator Timing Resistor Input. An RC network may be required to reduce jitter (see the Typical Application
Circuit).GNDGround ConnectionNDRVExternal n-Channel MOSFET Gate Connection
9VCCGate-Drive Supply. Internally generated supply from IN. Decouple VCC with a 10nF or larger capacitor
to GND.IN
IN Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX15000),
connect a startup resistor from the input supply line to IN. Connect the bias winding supply to IN also (see
the Typical Operating Circuit). For the MAX15001, connect IN directly to the 9.5V to 24V supply.
NDRV HIGH OUTPUT IMPEDANCE
vs. TEMPERATUREMAX15000 toc21
TEMPERATURE (°C)3510-15
SOURCING 20mA
ERROR AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCYFREQUENCY (Hz)
GAIN (dB)
PHASE (DEGREES)
-1600.1101001k10k100k1M10M100M
MAX15000 toc22
GAIN
PHASE
Typical Operating Characteristics (continued)(VUVLO/EN= +1.4V, VFB= +1V, COMP = open, VCS= 0V, TA= +25°C, unless otherwise noted.)
MAX15000/MAX15001
Detailed DescriptionThe MAX15000/MAX15001 current-mode PWM con-
trollers are ideal for isolated and nonisolated power-
supply applications. The devices offer an accurate
input startup voltage programmable through the
UVLO/EN input. This feature prevents the power supply
from entering a brownout condition in case the input
voltage sags below its minimum value. This is important
since switching power supplies increases their input
supply current as the input voltage drops to keep the
output power constant. In addition to this externally
adjustable UVLO feature, the MAX15000 also offers a
bootstrap UVLO with a large hysteresis (11.9V) and
very low startup and operating current, which result in
an efficient universal input power supply. The switching
frequency of the MAX15000/MAX15001 is programma-
ble with an external resistor.
The MAX15000 is well suited for universal input (recti-
fied 85VAC to 265VAC) or telecom (-36VDC to
-72VDC) power supplies. The MAX15001 is well suited
for low-input voltage (9.5VDC to 24VDC) power sup-
plies. The devices include an internal clamp at IN to
prevent the input voltage from exceeding the absolute
maximum rating (see Note 2 at the end of theElectrical
Characteristics table). The input is clamped when the
devices are started with a bleed resistor (R1 in Figure 1)
from a high input voltage and the UVLO/EN input is low.
The clamp can safely sink up to 2mA current.
Power supplies designed with the MAX15000 use a
high-value startup resistor R1 that charges a reservoir
capacitor C1 (see Figure1). During this initial period,
while the voltage is less than the internal bootstrap
UVLO threshold, the device typically consumes only
50µA 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 MAX15000/MAX15001 include a cycle-by-cycle
current limit that turns off the gate drive to the external
MOSFET whenever the internally set threshold of 1V is
exceeded. When using the MAX15000 in the boot-
strapped mode, if the power-supply output is shorted,
the tertiary winding voltage will drop below the internal-
ly set threshold causing the UVLO to turn off the gate
drive to the external power MOSFET. This will reinitiate
a startup sequence with soft-start.
Current-Mode PWM Controllers with
Programmable Switching FrequencyUVLO/ENIN4
VCC
NDRV
GND
UFLG
COMP5RTCS
R12C1
R11
VSUPPLY
R13
R14
VOUT
R15
MAX15000
Figure1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage
Current-Mode Control LoopThe advantages of current-mode control over voltage-
mode control are twofold. First, there is the feed-for-
ward characteristic brought on by the controller’s
ability to adjust for variations in the input voltage on a
cycle-by-cycle basis. Secondly, the stability require-
ments of the current-mode controller are reduced to
that of a single-pole system unlike the double pole in
voltage-mode control.
The MAX15000/MAX15001 use a current-mode control
loop where the output of the error amplifier (COMP) is
compared to the current-sense voltage at CS. When the
current-sense signal is lower than the noninverting
input of the PWM comparator, the output of the CPWM
comparator is low and the switch is turned on at each
clock pulse. When the current-sense signal is higher than
the inverting input of the CPWM, the output of the CPWM
comparator goes high and the switch is turned off.
Undervoltage LockoutThe MAX15000/MAX15001 provide a UVLO/EN input.
The threshold for UVLO is 1.23V with 60mV hysteresis.
Before any operation can commence, the voltage on
UVLO/EN has to exceed 1.23V. The UVLO circuit keeps
the CPWM comparator, ILIM comparator, oscillator,
and output driver shut down to reduce current con-
sumption (see the Functional Diagram).
Use this UVLO/EN input to program the input-supply
start voltage. For example, a reasonable start voltage
for a 36V to 72V telecom range is usually 34V.
Calculate the resistor-divider values, R2 and R3 (see
Figure1) by using the following formulas:
where IUVLOis the UVLO/EN input current (50nA max),
and VULR2is the UVLO/EN wake-up threshold (1.23V).
VINis the value of the input-supply voltage where the
power supply must start. The value of R3 is calculated
to minimize the voltage-drop error across R2 as a result
of the input bias current of the UVLO/EN input.
MAX15000 Bootstrap UVLOIn addition to the externally programmable UVLO func-
tion offered in both the MAX15000 and MAX15001, the
MAX15000 includes an internal bootstrap UVLOthat is
very useful when designing high-voltage power sup-
plies (see the Functional Diagram). This allows the
device to bootstrap itself during initial power-up. The
MAX15000 attempts to start when VINexceeds the
bootstrap UVLO threshold of 21.6V. During startup, the
UVLO circuit keeps the CPWM comparator, ILIM com-
parator, oscillator, and output driver shut down to
reduce current consumption. Once VIN reaches 21.6V,
the UVLO circuit turns on the CPWM and ILIM com-
parators, the oscillator, and allows the output driver to
switch. If VINdrops below 1.17V, the UVLO circuit shuts
down the CPWM comparator, ILIM comparator, oscilla-
tor, and output driver returning the MAX15000 to the
low-current startup mode.
Startup OperationThe MAX15001 starts up when the voltage at IN
exceeds 9.5V and the UVLO/EN input is greater than
1.23V. However, the MAX15000 requires that, in addi-
tion to meeting the specified startup conditions for the
MAX15001, the voltage at IN exceeds the bootstrap
UVLO threshold of 21.6V.
For the MAX15000, the voltage at IN is normally derived
from a tertiary winding of the transformer. However, at
startup there is no energy being delivered through the
transformer, hence, a special bootstrap sequence is
required. Figure2 shows the voltages at 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
Figure1). Only 50µA of the current supplied through R1
is used by the MAX15000, 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 reaches the
wake-up level of 21.6V. Once VINexceeds the boot-
strap UVLO threshold, NDRV begins switching the
MOSFET and transfers energy to the secondary and
tertiary outputs. If the voltage on the tertiary output
builds to higher than 9.74V (the bootstrap UVLO lowerVVVVVR
ULRIN
UVLOINULRULR
ULR500−−
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
