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19-3957; Rev 0; 1/06
Current-Mode PWM Controllers with Programmable Switching Frequency
General Description
The MAX15000/MAX15001 current-mode PWM controllers contain all the control circuitry required for the design of wide-input-voltage isolated and nonisolated power supplies. The MAX15000 is well suited for universal 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 voltage 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 210s internal delay, allows the sequencing of a secondary-side controller. The input-supply start voltage 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 startup. The MAX15001 does not have the internal bootstrap UVLO and can be biased directly from a minimum voltage 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% maximum duty-cycle limit. These devices are available in 10pin MAX(R) packages and are rated for operation over the -40C to +85C temperature range.
Features
Current-Mode Control Programmable Switching Frequency Up to 625kHz Accurate UVLO Threshold (1%) Open-Drain UVLO Flag Output with Internal Delay 36V to 72V Telecom Voltage Range Universal Offline Input Voltage Range Rectified 85VAC to 265VAC (MAX15000) 9.5V to 24V Input (MAX15001) Digital Soft-Start Internal Bootstrap UVLO with Large Hysteresis (MAX15000) Internal Error Amplifier with 1.5% Accurate Reference 50A (typ) Startup Supply Current 50% Maximum Duty-Cycle Limit (MAX15000A/MAX15001A) 75% Maximum Duty-Cycle Limit (MAX15000B/MAX15001B) 60ns Cycle-by-Cycle Current-Limit Propagation Delay Available in Tiny 10-Pin MAX Packages
MAX15000/MAX15001
Ordering Information
PART TEMP RANGE PINPACKAGE 10 MAX 10 MAX 10 MAX 10 MAX PKG CODE U10-2 U10-2 U10-2 U10-2
MAX15000AEUB+ -40C to +85C MAX15000BEUB+ MAX15001BEUB+ -40C to +85C -40C to +85C MAX15001AEUB+ -40C to +85C
Applications
1/2, 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
Selector Guide appears at end of data sheet. MAX is a registered trademark of Maxim Integrated Products, Inc.
Warning: The MAX15000/MAX15001 are designed to work with high voltages. Exercise caution. +Denotes lead-free package.
Pin Configuration
TOP VIEW
UVLO/EN 1 UFLG FB COMP CS 2 3 4 5 10 IN 9 VCC NDRV GND RT
MAX15000 MAX15001
8 7 6
MAX 1
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Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +30V IN Clamp (Internal Shunt) Current ........................................5mA VCC to 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 = +70C) 10-Pin MAX (derate 5.6mW/C above +70C) ........444.4mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range ............................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C
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.
ELECTRICAL CHARACTERISTICS
(VIN = +12V (for MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15k (MAX1500_A), R12 = 7.5k (MAX1500_B), R15 = 1k, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER UVLO/STARTUP Bootstrap UVLO Wake-Up Level Bootstrap UVLO Shutdown Level UVLO/EN Wake-Up Threshold UVLO/EN Shutdown Threshold UVLO/EN Input Current UVLO/EN Hysteresis IN Supply Current In UVLO IN Input Voltage Range UVLO/EN to UFLG Propagation Delay (Figure 3) UVLO/EN to NDRV Propagation Delay (Figure 3) Bootstrap UVLO Propagation Delay UFLG Low Output Voltage UFLG High Output Leakage Current INTERNAL SUPPLY VCC Regulator Set Point IN Supply Current After Startup Shutdown Supply Current VCCSP IIN VIN = 10.8V to 24V, sinking 1A to 20mA from VCC VIN = 24V UVLO/EN = low 7.0 2 50 10.5 4 90 V mA A tEXTR tEXTF tBUVR tBUVF VUFLG ISTART VIN VIN = 19V, MAX15000 only when in bootstrap UVLO MAX15001 only UVLO/EN steps up from 1V to 1.4V UVLO/EN steps down from 1.4V to 1V UVLO/EN steps up from 1V to 1.4V UVLO/EN steps down from 1.4V to 1V VIN steps up from 9V to 24V (MAX15000 only) VIN steps down from 24V to 9V (MAX15000 only) IUFLG = 5mA sinking VUFLG = 25V 0.1 150 9.5 3 0.6 3 210 5 s 1 0.8 1 V A 10 300 VSUVR VSUVF VULR2 VULF2 IUVLO VIN rising (MAX15000 only) VIN falling (MAX15000 only) UVLO/EN rising UVLO/EN falling VUVLO/EN 2V 19.68 9.05 1.218 1.14 -50 60 50 90 24.0 21.6 9.74 1.23 1.17 23.60 10.43 1.242 1.20 +50 V V V V nA mV A V s ms s SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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Current-Mode PWM Controllers with Programmable Switching Frequency
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V (for MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15k (MAX1500_A), R12 = 7.5k (MAX1500_B), R15 = 1k, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER GATE DRIVER Driver Output Impedance Driver Peak Sink Current Driver Peak Source Current PWM COMPARATOR Comparator Offset Voltage CS Input Bias Current Comparator Propagation Delay CURRENT-LIMIT COMPARATOR Current-Limit Trip Threshold CS Input Bias Current Propagation Delay From Comparator Input to NDRV IN CLAMP VOLTAGE IN Clamp Voltage ERROR AMPLIFIER Voltage Gain Unity-Gain Bandwidth Phase Margin FB Input Offset Voltage COMP High Voltage COMP Low Voltage Source Current Sink Current Reference Voltage Reference Voltage Accuracy FB Input Bias Current COMP Short-Circuit Current DIGITAL SOFT-START Soft-Start Duration Reference Voltage Steps During Soft-Start Reference Voltage Step tSS fSW = 350kHz 1984 5.6 31 39.67 NDRV cycles ms steps mV VREF (Note 3) -1.5 -50 8 ICOMP = 0 ICOMP = 0 0.5 0.5 1.230 +1.5 +50 2.8 1.1 RLOAD = 100k RLOAD = 100k, CLOAD = 200pF RLOAD = 100k, CLOAD = 200pF 80 2 65 1 dB MHz degrees mV V mA mA V % nA mA VINC 2mA sink current (Note 2) 24.1 26.1 29.0 V VCS ICS tPDCS VCS = 0V 100mV overdrive 900 -4 60 1000 1100 +4 mV A ns VPWM ICS tPWM VCOMP - VCS VCS = 0V Change in VCS = 0.1V 1.24 -4 60 1.38 1.54 +4 V A ns RON(LOW) Measured at NDRV sinking 100mA RON(HIGH) Measured at NDRV sourcing 20mA 2 4 1 0.65 4 10 A A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX15000/MAX15001
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3
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V (for MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15k (MAX1500_A), R12 = 7.5k (MAX1500_B), R15 = 1k, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER OSCILLATOR Oscillator Frequency Range Oscillator Frequency Accuracy NDRV Switching Frequency (Note 4) Maximum Duty Cycle fSW DMAX fOSC fOSC = 200kHz to 800kHz fOSC = 50kHz to 2500kHz MAX1500_A, fSW = fOSC/2 MAX1500_B, fSW = fOSC/4 MAX1500_A MAX1500_B 50 -10 -20 25 12.5 50 75 2500 +10 +20 625 625.0 kHz % kHz % SYMBOL CONDITIONS MIN TYP MAX UNITS
Note 1: All devices are 100% tested at TA = +85C. 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 Figure 1) 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: VREF is 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).
Typical Operating Characteristics
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25C, unless otherwise noted.)
BOOTSTRAP UVLO WAKE-UP LEVEL vs. TEMPERATURE
MAX15000 toc01
BOOTSTRAP UVLO SHUTDOWN LEVEL vs. TEMPERATURE
MAX15000 toc02
UVLO/EN WAKE-UP THRESHOLD vs. TEMPERATURE
UVLO/EN RISING 1.234 1.232 1.230 1.228
MAX15000 toc03
21.8 MAX15000 VIN RISING 21.7
10.3 MAX15000 VIN FALLING 10.1
1.236
VIN (V)
21.5
VIN (V)
21.6
9.9
9.7
21.4
9.5
UVLO/EN (V) -15 10 35 60 85
1.226 1.224 -40
21.3 -40
-15
10
35
60
85
9.3 -40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
4
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Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25C, unless otherwise noted.)
UVLO/EN SHUTDOWN THRESHOLD vs. TEMPERATURE
UVLO/EN FALLING 1.175 1.170 ISTART (A) 1.165 1.160 50 1.155 1.150 -40 45 -40 1.6 55 IIN (mA) 1.8
MAX15000 toc04
VIN SUPPLY CURRENT IN UVLO vs. TEMPERATURE
MAX15000 toc05
VIN SUPPLY CURRENT AFTER STARTUP vs. TEMPERATURE
VIN = 24V fSW = 350kHz 1.9
MAX15000 toc06
1.180
65 VIN = 19V MAX15000 WHEN IN BOOTSTRAP UVLO 60
2.0
VUVLO/EN (V)
1.7
-15
10
35
60
85
-15
10
35
60
85
1.5 -40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
VCC REGULATOR SET POINT vs. TEMPERATURE
VIN = 19V NDRV NOT SWITCHING 9.6 VCC (V) VCC (V)
MAX15000 toc07
VCC REGULATOR SET POINT vs. TEMPERATURE
MAX15000 toc08
CURRENT-LIMIT TRIP THRESHOLD vs. TEMPERATURE
CURRENT-LIMIT TRIP THRESHOLD (V) +3 1.01 1.00 MEAN 0.99 0.98 -3 0.97 TOTAL NUMBER OF DEVICES = 140 0.96
MAX15000 toc09
9.8
8.9 VIN = 19V 8.8 8.7 8.6 10mA LOAD
1.02
9.4 NDRV SWITCHING fSW = 350kHz 9.2
8.5 8.4 20mA LOAD 8.3 8.2
9.0 -40
8.1 -15 10 35 60 85 -40 -20 0 20 40 60 80 TEMPERATURE (C) TEMPERATURE (C)
-40
-15
10
35
60
85
TEMPERATURE (C)
CURRENT-LIMIT TRIP THRESHOLD
MAX15000 toc10
SWITCHING FREQUENCY vs. TEMPERATURE
MAX15000 toc11
SWITCHING FREQUENCY
TOTAL NUMBER OF DEVICES = 140
MAX15000 toc12
60 50 PERCENTAGE OF UNITS (%) 40 30 20 10 0 0.964
355 +3 SWITCHING FREQUENCY (kHz) 350 345 MEAN 340 335 -3 330 TOTAL NUMBER OF DEVICES = 140 325
TOTAL NUMBER OF DEVICES = 140
60 50 PERCENTAGE OF UNITS (%) 40 30 20 10 0 326.7
0.978
0.993
1.007
1.022
1.036
-40
-15
10
35
60
85
333.5
340.3
347.2
354.0
360.8
CURRENT-LIMIT TRIP THRESHOLD (V)
TEMPERATURE (C)
SWITCHING FREQUENCY (kHz)
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5
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25C, unless otherwise noted.)
PROPAGATION DELAY FROM CURRENT-LIMIT COMPARATOR INPUT TO NDRV vs. TEMPERATURE
MAX15000 toc13 MAX15000 toc14
SWITCHING FREQUENCY vs. TIMING RESISTOR
1000 60 MAX15000A
UVLO/EN TO NDRV PROPAGATION DELAY vs. TEMPERATURE
MAX15000 toc15
6 5 UVLO DELAY (ms) 4 3 2 1 206s UVLO/EN FALLING
SWITCHING FREQUENCY (kHz)
55 tPDCS (ns)
UVLO/EN RISING
100
50
45
10 1 10 100 1000 TIMING RESISTOR (k)
40 -40 -15 10 35 60 85 TEMPERATURE (C)
0 -40 -15 10 35 60 85 TEMPERATURE (C)
UVLO/EN TO UFLG PROPAGATION DELAY vs. TEMPERATURE
MAX15000 toc16
REFERENCE VOLTAGE vs. TEMPERATURE
MAX15000 toc17
INPUT CURRENT vs. IN VOLTAGE
UVLO/EN = 1.4V NDRV SWITCHING AT 350kHz 1.76 INPUT CURRENT (mA)
MAX15000 toc18
6 5 UVLO DELAY (s) 4 3 2 UVLO/EN FALLING 1 0 -40 -15 10 35 60 UVLO/EN RISING
1.232 VIN = 12V REFERENCE VOLTAGE (V) 1.231
1.80
1.72
1.230
1.68
1.229
1.64
1.228 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
1.60 10 11 12 13 14 15 16 17 18 19 IN VOLTAGE (V)
INPUT CLAMP VOLTAGE vs. TEMPERATURE
MAX15000 toc19
NDRV LOW OUTPUT IMPEDANCE vs. TEMPERATURE
VIN = 24V SINKING 100mA
MAX15000 toc20
27.0 26.8 INPUT CLAMP VOLTAGE (V) 26.6 26.4 IIN = 2mA
2.4 2.2 2.0 RON () 1.8 1.6 1.4 1.2
26.2 26.0 25.8 25.6 25.4 25.2 25.0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
-40
-15
10
35
60
85
TEMPERATURE (C)
6
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Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25C, unless otherwise noted.)
NDRV HIGH OUTPUT IMPEDANCE vs. TEMPERATURE
SOURCING 20mA
MAX15000 toc21
ERROR AMPLIFIER OPEN-LOOP GAIN AND PHASE vs. FREQUENCY
100 80 60 40 GAIN (dB) 20 0 -20 PHASE GAIN
MAX15000 toc22
5.0
120 80 40 0 -40 -80 -120 -160 PHASE (DEGREES)
4.6
RON ()
4.2
3.8
3.4 -40 3.0 -40 -15 10 35 60 85 TEMPERATURE (C) -60 0.1 1 10 100 -200 1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
Pin Description
PIN 1 NAME FUNCTION Externally Programmable Undervoltage Lockout. UVLO/EN programs the input start voltage. Connect UVLO/EN UVLO/EN to GND to disable the device. NDRV stops switching approximately 210s after the UVLO/EN voltage falls below 1.17V. UFLG FB COMP CS Open-Drain Undervoltage Flag Output. UFLG is asserted low as soon as the UVLO/EN voltage falls below its threshold. Error-Amplifier Inverting Input Error-Amplifier Output 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. Oscillator Timing Resistor Input. An RC network may be required to reduce jitter (see the Typical Application Circuit). Ground Connection External n-Channel MOSFET Gate Connection Gate-Drive Supply. Internally generated supply from IN. Decouple VCC with a 10nF or larger capacitor to GND. 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.
2 3 4 5
6 7 8 9
RT GND NDRV VCC
10
IN
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7
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Detailed Description
The MAX15000/MAX15001 current-mode PWM controllers are ideal for isolated and nonisolated powersupply 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 programmable with an external resistor. The MAX15000 is well suited for universal 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 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 the Electrical 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 Figure 1). During this initial period, while the voltage is less than the internal bootstrap UVLO threshold, the device typically consumes only 50A 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 bootstrapped mode, if the power-supply output is shorted, the tertiary winding voltage will drop below the internally 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.
D2
T1
D1 VSUPPLY R2 UVLO/EN UFLG FB C2 C5 R11 R3 COMP CS 1 2 3 4 5 10 9 8 7 6 IN VCC NDRV GND RT Q1 R1 R13 VOUT
MAX15000
C4
R14 C6 C2 R15 R12 C1 R4
0V
Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage 8 _______________________________________________________________________________________
Current-Mode PWM Controllers with Programmable Switching Frequency
Current-Mode Control Loop
The advantages of current-mode control over voltagemode control are twofold. First, there is the feed-forward 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 requirements 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.
MAX15000 Bootstrap UVLO
In addition to the externally programmable UVLO function offered in both the MAX15000 and MAX15001, the MAX15000 includes an internal bootstrap UVLO that is very useful when designing high-voltage power supplies (see the Functional Diagram). This allows the device to bootstrap itself during initial power-up. The MAX15000 attempts to start when V IN exceeds the bootstrap UVLO threshold of 21.6V. During startup, the UVLO circuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver shut down to reduce current consumption. Once VIN reaches 21.6V, the UVLO circuit turns on the CPWM and ILIM comparators, the oscillator, and allows the output driver to switch. If VIN drops below 1.17V, the UVLO circuit shuts down the CPWM comparator, ILIM comparator, oscillator, and output driver returning the MAX15000 to the low-current startup mode.
MAX15000/MAX15001
Undervoltage Lockout
The 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 consumption (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 Figure 1) by using the following formulas: R3 VULR2 VIN 500 IUVLO (VIN - VULR2 )
Startup Operation
The 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 addition 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. Figure 2 shows the voltages at IN and VCC during startup. Initially, both VIN and VCC are 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 1). Only 50A 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 VCC voltage reaches approximately 9.5V, while the voltage across C1 continues rising until it reaches the wake-up level of 21.6V. Once VIN exceeds the bootstrap 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 lower
V -V R2 = IN ULR2 R 3 VULR2 where IUVLO is the UVLO/EN input current (50nA max), and VULR2 is the UVLO/EN wake-up threshold (1.23V). VIN is 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.
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9
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
threshold), then startup has been accomplished and sustained operation will commence. If VIN drops below 9.74V before startup is complete, the device goes back to low-current UVLO. In this case, increase the value of C1 to store enough energy to allow for the voltage at the tertiary winding to build up.
UVLO Flag (UFLG)
The MAX15000/MAX15001 have an open-drain undervoltage flag output (UFLG). When used with an optocoupler the UFLG output can serve to sequence a secondary-side controller. An internal 210s delay occurs the instant the voltage on UVLO/EN drops below 1.17V until NDRV stops switching. This allows for the UFLG output to change state before the MAX15000/ MAX15001 shut down (Figure 3). When the voltage at the UVLO/EN is above the threshold, UFLG is high impedance. When UVLO/EN is below the threshold, UFLG goes low. UFLG is not affected by bootstrap UVLO (MAX15000).
MAX15000 fig02
Soft-Start
VCC 2V/div
VIN 5V/div
0V
100ms/div
The MAX15000/MAX15001 soft-start feature allows the output voltage to ramp up in a controlled manner, eliminating voltage overshoot. The MAX15000/MAX15001 reference generator that is internally connected to the error amplifier soft-starts to achieve superior control of the output voltage under heavy and light load conditions. Soft-start begins after UVLO is deasserted (VIN is above 21.6V for the MAX15000, VIN is above 9.5V for the MAX15001, and the voltage on UVLO/EN is above 1.23V). The voltage applied to the noninverting node of the amplifier ramps from 0 to 1.23V in 1984 NDRV switching cycles. Use the following formula to calculate the soft-start time (tSS): t SS = 1984 fNDRV
Figure 2. VIN and VCC During Startup When Using the MAX15000 in Bootstrapped Mode (Figure 1)
where fNDRV is the switching frequency at the NDRV output. Figure 4 shows the soft-start regulated output of a power supply using the MAX15000 during startup.
1.23V (1%) VUVLO/EN Hi-Z VUFLG LOW 3s VNDRV
1.17V (typ)
0.6s NDRV SWITCHING
LOW
SHUTDOWN tEXTR 3ms tEXTF 210s
SHUTDOWN
Figure 3. UVLO/EN and UFLG Operation Timing 10 ______________________________________________________________________________________
Current-Mode PWM Controllers with Programmable Switching Frequency
n-Channel MOSFET Switch Driver
The NDRV output drives an external n-channel MOSFET. The internal regulator output (VCC), set to approximately 9V, drives NDRV. For the universal input voltage range, the MOSFET used must withstand the DC level of the high-line input voltage plus the reflected voltage at the primary of the transformer. Most applications that use the discontinuous flyback topology require a MOSFET rated at 600V. NDRV can source/sink in excess of 650/1000mA peak current; therefore, select a MOSFET that will yield acceptable conduction and switching losses.
MAX15000 fig04
MAX15000/MAX15001
VOUT 2V/div
Oscillator/Switching Frequency
Use an external resistor at RT to program the MAX15000/MAX15001 internal oscillator frequency between 50kHz and 2.5MHz. The MAX15000A/ MAX15001A output switching frequency is one-half of the programmed oscillator frequency with a 50% duty cycle. The MAX15000B/MAX15001B output switching frequency is one-quarter of the programmed oscillator frequency with a 75% duty cycle. The MAX15000A/MAX15001A and MAX15000B/ MAX15001B have programmable output switching frequencies from 25kHz to 625kHz and 12.5kHz to 625kHz, respectively. Use the following formulas to determine the appropriate value of the resistor R12 (see Figure 1) needed to generate the desired output switching frequency (fSW) at the NDRV output: R12 = R12 = 1010 for the MAX15000A / MAX15001A. 2fSW 1010 for the MAX15000B / MAX15001 . B 4fSW
100mA LOAD ON/VOUT1 100mA LOAD ON/VOUT2
2ms/div
Figure 4. Primary-Side Output Voltage Soft-Start During Initial Startup for the Circuit in Figure 6
Internal Error Amplifier
The MAX15000/MAX15001 include an internal error amplifier to regulate the output voltage in the case of a nonisolated power supply (see Figure 1). For the circuit in Figure 1, calculate the output voltage using the following equation: R13 VOUT = 1+ V R14 REF where VREF = 1.23V. The amplifier's noninverting input is internally connected to a digital soft-start circuit that gradually increases the reference voltage during startup applied to this input. This forces the output voltage to come up in an orderly and well-defined manner under all load conditions. The error amplifier may also be used to regulate the tertiary winding output which implements a primary-sideregulated, isolated power supply (see Figure 6). For the circuit in Figure 6, calculate the output voltage using the following equation: N R1 VOUT = S 1+ VREF + VD6 - VD2 NT R2 where NS is the number of secondary winding turns, NT is the number of tertiary winding turns, and both V D6 and VD2 are the diode drops at the respective outputs.
where R12 is the resistor connected from RT to GND (see Figure 1). Connect an RC network in parallel with R12 as shown in Figure 1. The RC network should consist of a 100nF capacitor C6 (for stability) in series with resistor R15 which serves to further minimize jitter. Use the following formula to determine the value of R15: R15 = 88.9 x (R12) 4
1
For example, if R12 is 4k, R15 becomes 707.
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11
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Current Limit
The current-sense resistor (R4 in Figure 1), connected between the source of the MOSFET and ground, sets the current limit. The current-limit comparator has a voltage trip level (VCS) of 1V. Use the following equation to calculate the value of R4: V R4 = CS IPRI where IPRI is the peak current in the primary side of the transformer which also flows through the MOSFET. When the voltage produced by this current (through the current-sense resistor) exceeds the current-limit comparator threshold, the MOSFET driver (NDRV) terminates the current on-cycle within 60ns (typ). Use a small RC network to filter out the leading-edge spikes on the sensed waveform when needed. Set the corner frequency between 2MHz and 10MHz. when fSW = 350kHz), C1 must store enough charge to deliver current to the device for at least this much time. To calculate the approximate amount of capacitance required, use the following formula: Ig = Qgtot fSW C1 = (IIN + Ig )(t SS ) VHYST
where IIN is the MAX15000's internal supply current (2mA) after startup, Qgtot is the total gate charge for Q1, f SW is the MAX15000's switching frequency (350kHz), V HYST is the bootstrap UVLO hysteresis (approximately 12V) and tSS is the internal soft-start time (5.6ms). Example: Ig = (8nC) (350kHz) 2.8mA C1 = (2mA + 2.8mA)(5.6ms) = 2.24F 12V
Applications Information
Startup Time Considerations for Power Supplies Using the MAX15000
The bypass capacitor at IN, C1, supplies current immediately after the MAX15000 wakes up (see Figure 1). The size of C1 and the connection configuration of the tertiary winding determine the number of cycles available for startup. Large values of C1 increase the startup time but also supply gate charge for more cycles during initial startup. If the value of C1 is too small, VIN drops below 9.74V because NDRV does not have enough time to switch and build up sufficient voltage across the tertiary output which powers the device. The device goes back into UVLO and does not start. Use a low-leakage capacitor for C1 and C2. Typically, offline power supplies keep startup times to less than 500ms even in low-line conditions (85VAC input for universal offline or 36VDC for telecom applications). Size the startup resistor, R1, to supply both the maximum startup bias of the device (90A) and the charging current for C1 and C2. The bypass capacitor, C2, must charge to 9.5V and C1 to 24V, all within the desired time period of 500ms. Because of the internal soft-start time of the MAX15000 (approximately 5.6ms
Choose a 2.2F standard value (assuming 350kHz switching frequency). Assuming C1 > C2, calculate the value of R1 as follows: V C1 IC1 = SUVR (500ms) VIN(MIN) - VSUVR R1 IC1 + ISTART where VIN(MIN) is the minimum input supply voltage for the application (36V for telecom), VSUVR is the bootstrap UVLO wake-up level (23.6V max), ISTART is the IN supply current at startup (90A max). For example: (24V)(2.2F) = 0.105mA (500ms) (36V) - (12V) R1 = 123.07k (0.105mA) + (90A) IC1 = Choose a 120k standard value.
12
______________________________________________________________________________________
Current-Mode PWM Controllers with Programmable Switching Frequency
Choose a higher value for R1 than the one calculated in the previous equation if a longer startup time can be tolerated to minimize power loss on this resistor. The above startup method is applicable to a circuit similar to the one shown in Figure 1. In this circuit, the tertiary winding has the same phase as the output windings. Thus, the voltage on the tertiary winding at any given time is proportional to the output voltage and goes through the same soft-start period as the output voltage. The minimum discharge time of C1 from 21.6V to 9.74V must be greater than the soft-start time of 5.6ms. Another method for bootstrapping the power supply is to use a bias winding that is in phase with the MOSFET on-time (see Figure 5). In this case, the amount of capacitance required at IN (C1) is much smaller. However, the input voltage cannot have a range greater than approximately 2:1 (primary winding voltage to bias winding voltage ratio). For hiccup-mode fault protection, make the bias winding in phase with the output, then the power-supply hiccups and soft-starts under output short-circuit conditions. The power supply does not hiccup if the bias winding is in phase with the MOSFET on-time.
MAX15000/MAX15001
D1 T1 D2 VIN C4 R1 R2 R8 IN U2 OPTO TRANS. C1 R5 FB RT C6 R6 C2 R12 R15 R3 UVLO/EN R4 VCC R7 COMP GND U3 TL431 R10 R9 VOUT
UFLG
U1 MAX15000A
NDRV CS
Q1 U2 OPTO LED C3
Figure 5. Secondary-Side Regulated, Isolated Power Supply
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13
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
IN D8 C16 1F 35V C12 15F 35V FB_P D6 R7 1.2k R12 1.2k D7 OPEN L2 15T 4 8 3 C1 1F 100V C2 1F 100V R8 OPEN C10 OPEN D3 OPEN R1 22.6k 1% R2 +VIN 2.49k 1% R3 1.37M 1% R9 75k 1% C9 100pF 4 C14 3900pF 1 C17 OPEN 9 C7 0.22F SHDN 1 JU1 2 R13 10k UFLG_PULL UFLG 2 VCC GND 7 COMP IN 3 FB IN 10 C11 0.22F R10 4.7 R11 100 C8 OPEN 56 4 1 2 7 8 28T 35H 2 6 1 C6 0.0047F 250VAC 7 5T D1 C3 68F 6.3V D4 L1 5V/1.5A C13 1F VOUT1 C4 22F SGND 6.3V 5 T1 9 10 12T D2 C5 47F 25V VOUT2 15V/100mA D5 C15 1F SGND
36V TO 72V +VIN +VIN -VIN
R6 33k
FB_P
U1 MAX15000A
NDRV
8
N1 IRF7464 3
UVLO/EN
CS
5
R4 51.1k
R5 0.600 1%
UFLG
RT
6 R14 14.3k 1% R15 750 C18 0.1F C19 OPEN
NOTE: MOSFET N1 = IR IRF7464.
Figure 6. Primary-Side-Regulated, Dual-Output, Isolated Telecom Power Supply
Primary-Side-Regulated, Isolated Telecom Power Supply
Figure 6 shows a complete circuit of a dual-output power supply with a telecom voltage range of 36V to 72V. An important aspect of this power supply is that it is primary-side regulated. The regulation through the tertiary winding also supplies bias for the MAX15000. In the circuit of Figure 6, cross-regulation has been improved (tertiary and 5V outputs) by using chip inductors, L1 and L2, and R7||R12 across C12. R7||R12 presents enough loading on the tertiary winding output to allow 10% load regulation on the 5V output over a load current range from 150mA to 1.5A (Figure 7).
5.6 5.5 5.4 VOUT (V) 5.3 5.2 5.1 5.0 4.9 4.8
5V OUTPUT LOAD REGULATION
NO LOAD AT 15V OUTPUT VIN+ = 40V VIN- = 0V
MAX15000 fig07
0.15 0.30 0.45 0.60 0.75 0.90 1.05 1.20 1.35 1.50 IOUT (A)
Figure 7. Output Voltage Regulation for the Circuit in Figure 6 14 ______________________________________________________________________________________
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
L1 12V D1 15V
UFLG IN VCC C3 C1 C2 COMP FB GND NDRV
R2 R5 Q1
MAX15001
CS C4 R1
RT
UVLO/EN
C6 R3 R12 0V R15
R6
Figure 8. 12V to 15V Output Boost Regulator
Layout Recommendations
Typically, there are two sources of noise emission in a switching power supply: high di/dt loops and high dv/dt surfaces. For example, traces that carry the drain current often form high di/dt loops. Similarly, the heatsink of the MOSFET presents a dv/dt source; therefore, minimize the surface area of the heatsink as much as possible. Keep all PC board traces carrying switching currents as short as possible to minimize current loops.
Use a ground plane for best results. The pins of the MAX package are positioned to allow easy interfacing to the external MOSFET. For universal AC input design, follow all applicable safety regulations. Offline power supplies may require UL, VDE, and other similar agency approvals. To avoid noise coupling of signals from RT to NDRV, route traces from RT away from NDRV.
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15
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Typical Application Circuit
D2
T1
D1 R5 R2 UVLO/EN UFLG FB + 36V TO 72V C5 R3 C2 COMP R11 CS 1 2 3 4 5 10 9 8 7 6 IN VCC NDRV GND RT Q1 R1 C4 VOUT
MAX15000
R6 C6 C2 R15 R12 C1 R4
16
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Current-Mode PWM Controllers with Programmable Switching Frequency
Functional Diagram
MAX15000/MAX15001
IN
IN CLAMP 26.1V DIGITAL SOFT-START REFERENCE 1.23V 21.6V 9.74V
IN
VCC REGULATOR
VCC
BOOTSTRAP UVLO REG_OK * VL
(INTERNAL 5.25V SUPPLY) 210s DELAY
UFLG N
UVLO/EN 1.23V 1.17V COMP
UVLO
DRIVER FB ERROR AMP CPWM 1.4V CS GND VCS 1V ILIM OSCILLATOR S Q R NDRV
MAX15000 MAX15001
RT
*MAX15000 ONLY
Selector Guide
PART MAX15000A MAX15000B MAX15001A* MAX15001B* BOOTSTRAP STARTUP VOLTAGE (V) UVLO Yes Yes No No 22 22 9.5 9.5 MAX DUTY CYCLE (%) 50 75 50 75
Chip Information
PROCESS: BiCMOS
*The MAX15001 does not have an internal bootstrap UVLO. The MAX15001 starts operation as long as VIN is higher than 9.5V and UVLO/EN is higher than 1.23V.
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17
Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000/MAX15001
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
10LUMAX.EPS
1 1
e
10
4X S
10
INCHES MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S 0 6
MILLIMETERS MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.090 0.200 0.498 REF 0 6
H
O0.500.1
0.60.1
1
1
0.60.1
TOP VIEW
BOTTOM VIEW
D2 GAGE PLANE A2 A b A1 D1
E2
c
E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products
Heaney
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.

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