19-3957; Rev 0; 1/06
KIT
ATION
EVALU
E
L
B
AVAILA
Current-Mode PWM Controllers with
Programmable Switching Frequency
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 210µs 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 µMAX® packages and are rated for operation over the
-40°C to +85°C temperature range.
Applications
1/2, 1/4, and 1/8th Brick Power Modules
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
50µA (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 µMAX Packages
Ordering Information
PINPACKAGE
PKG
CODE
MAX15000AEUB+ -40°C to +85°C
10 µMAX
U10-2
MAX15000BEUB+
-40°C to +85°C
10 µMAX
U10-2
MAX15001AEUB+ -40°C to +85°C
10 µMAX
U10-2
MAX15001BEUB+
10 µMAX
U10-2
PART
TEMP RANGE
-40°C to +85°C
Warning: The MAX15000/MAX15001 are designed to work with
high voltages. Exercise caution.
+Denotes lead-free package.
Pin Configuration
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
TOP VIEW
10 IN
UVLO/EN 1
UFLG
2
MAX15000
MAX15001
9
VCC
8
NDRV
FB
3
COMP
4
7
GND
CS
5
6
RT
Selector Guide appears at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
µMAX
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX15000/MAX15001
General Description
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
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 = +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
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 = 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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UVLO/STARTUP
Bootstrap UVLO Wake-Up Level
VSUVR
VIN rising (MAX15000 only)
19.68
21.6
23.60
V
Bootstrap UVLO Shutdown Level
VSUVF
VIN falling (MAX15000 only)
9.05
9.74
10.43
V
UVLO/EN Wake-Up Threshold
VULR2
UVLO/EN rising
1.218
1.23
1.242
V
UVLO/EN Shutdown Threshold
VULF2
UVLO/EN falling
1.14
1.17
1.20
V
UVLO/EN Input Current
IUVLO
VUVLO/EN ≤ 2V
-50
+50
nA
ISTART
VIN = 19V, MAX15000 only when in
bootstrap UVLO
UVLO/EN Hysteresis
IN Supply Current In UVLO
IN Input Voltage Range
60
VIN
Bootstrap UVLO Propagation
Delay
UFLG Low Output Voltage
9.5
UVLO/EN steps up from 1V to 1.4V
UVLO/EN to UFLG Propagation
Delay (Figure 3)
UVLO/EN to NDRV Propagation
Delay (Figure 3)
MAX15001 only
50
90
µA
24.0
V
3
UVLO/EN steps down from 1.4V to 1V
µs
0.6
tEXTR
UVLO/EN steps up from 1V to 1.4V
tEXTF
UVLO/EN steps down from 1.4V to 1V
tBUVR
VIN steps up from 9V to 24V (MAX15000
only)
5
tBUVF
VIN steps down from 24V to 9V
(MAX15000 only)
1
VUFLG
IUFLG = 5mA sinking
UFLG High Output Leakage
Current
mV
150
3
10
ms
210
300
µs
µs
VUFLG = 25V
0.1
0.8
V
1
µA
10.5
V
INTERNAL SUPPLY
VCC Regulator Set Point
IN Supply Current After Startup
Shutdown Supply Current
2
VCCSP
IIN
VIN = 10.8V to 24V, sinking 1µA to 20mA
from VCC
7.0
VIN = 24V
2
4
mA
UVLO/EN = low
50
90
µA
_______________________________________________________________________________________
Current-Mode PWM Controllers with
Programmable Switching Frequency
(VIN = +12V (for MAX15000, bring VIN up 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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GATE DRIVER
Driver Output Impedance
RON(LOW) Measured at NDRV sinking 100mA
2
4
RON(HIGH) Measured at NDRV sourcing 20mA
4
10
Driver Peak Sink Current
Driver Peak Source Current
Ω
1
A
0.65
A
PWM COMPARATOR
Comparator Offset Voltage
CS Input Bias Current
Comparator Propagation Delay
VPWM
ICS
tPWM
VCOMP - VCS
VCS = 0V
1.24
1.38
-4
Change in VCS = 0.1V
1.54
V
+4
µA
60
ns
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold
VCS
CS Input Bias Current
ICS
Propagation Delay From
Comparator Input to NDRV
900
VCS = 0V
tPDCS
100mV overdrive
VINC
2mA sink current (Note 2)
1000
-4
1100
mV
+4
µA
60
ns
IN CLAMP VOLTAGE
IN Clamp Voltage
24.1
26.1
29.0
V
ERROR AMPLIFIER
Voltage Gain
RLOAD = 100kΩ
80
dB
Unity-Gain Bandwidth
RLOAD = 100kΩ, CLOAD = 200pF
2
MHz
Phase Margin
RLOAD = 100kΩ, CLOAD = 200pF
65
degrees
±1
mV
FB Input Offset Voltage
COMP High Voltage
ICOMP = 0
COMP Low Voltage
ICOMP = 0
2.8
1.1
V
Source Current
0.5
mA
Sink Current
0.5
mA
Reference Voltage
VREF
(Note 3)
1.230
V
Reference Voltage Accuracy
-1.5
+1.5
%
FB Input Bias Current
-50
+50
nA
COMP Short-Circuit Current
8
mA
1984
NDRV
cycles
5.6
ms
31
steps
39.67
mV
DIGITAL SOFT-START
Soft-Start Duration
tSS
fSW = 350kHz
Reference Voltage Steps During
Soft-Start
Reference Voltage Step
_______________________________________________________________________________________
3
MAX15000/MAX15001
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V (for MAX15000, bring VIN up 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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
kHz
OSCILLATOR
Oscillator Frequency Range
fOSC
Oscillator Frequency Accuracy
NDRV Switching Frequency
(Note 4)
fSW
Maximum Duty Cycle
DMAX
50
2500
fOSC = 200kHz to 800kHz
-10
+10
fOSC = 50kHz to 2500kHz
-20
+20
MAX1500_A, fSW = fOSC/2
25
625
MAX1500_B, fSW = fOSC/4
12.5
625.0
MAX1500_A
50
MAX1500_B
75
%
kHz
%
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 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 = +25°C, unless otherwise noted.)
21.7
10.1
VIN (V)
21.6
MAX15000 VIN FALLING
21.5
1.236
UVLO/EN RISING
1.234
UVLO/EN (V)
MAX15000 VIN RISING
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
MAX15000 toc02
10.3
MAX15000 toc01
21.8
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
9.9
9.7
MAX15000 toc03
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
VIN (V)
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
1.232
1.230
1.228
21.4
21.3
-40
9.5
-15
10
35
TEMPERATURE (°C)
4
60
85
9.3
-40
1.226
-15
10
35
TEMPERATURE (°C)
60
85
1.224
-40
-15
10
35
TEMPERATURE (°C)
_______________________________________________________________________________________
60
85
Current-Mode PWM Controllers with
Programmable Switching Frequency
1.175
2.0
MAX15000 toc05
UVLO/EN FALLING
VIN SUPPLY CURRENT AFTER
STARTUP vs. TEMPERATURE
65
MAX15000 toc04
1.180
VIN SUPPLY CURRENT IN UVLO
vs. TEMPERATURE
VIN = 19V
MAX15000 WHEN IN
BOOTSTRAP UVLO
VIN = 24V
fSW = 350kHz
1.9
60
1.165
IIN (mA)
1.170
ISTART (µA)
VUVLO/EN (V)
MAX15000 toc06
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
55
1.8
1.7
1.160
50
1.6
1.155
-15
10
35
60
45
-40
85
-15
10
35
60
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
VCC REGULATOR SET POINT
vs. TEMPERATURE
VCC REGULATOR SET POINT
vs. TEMPERATURE
CURRENT-LIMIT TRIP THRESHOLD
vs. TEMPERATURE
VIN = 19V
8.8
8.7
9.6
10mA LOAD
VCC (V)
8.6
9.4
NDRV SWITCHING
fSW = 350kHz
8.5
8.4
20mA LOAD
8.3
9.2
8.2
1.02
MAX15000 toc09
NDRV NOT SWITCHING
8.9
CURRENT-LIMIT TRIP THRESHOLD (V)
VIN = 19V
MAX15000 toc08
9.8
VCC (V)
1.5
-40
85
TEMPERATURE (°C)
MAX15000 toc07
1.150
-40
+3σ
1.01
1.00
MEAN
0.99
0.98
-3σ
0.97
TOTAL NUMBER OF DEVICES = 140
8.1
35
60
-20
0
20
40
60
TEMPERATURE (°C)
CURRENT-LIMIT TRIP THRESHOLD
SWITCHING FREQUENCY
vs. TEMPERATURE
40
30
20
-40
10
35
60
85
SWITCHING FREQUENCY
+3σ
350
345
MEAN
340
335
-3σ
330
10
-15
TEMPERATURE (°C)
MAX15000 toc11
TOTAL NUMBER
OF DEVICES = 140
50
80
355
SWITCHING FREQUENCY (kHz)
60
PERCENTAGE OF UNITS (%)
-40
85
TEMPERATURE (°C)
60
TOTAL NUMBER
OF DEVICES = 140
50
MAX15000 toc12
10
0.96
PERCENTAGE OF UNITS (%)
-15
MAX15000 toc10
9.0
-40
40
30
20
10
TOTAL NUMBER OF DEVICES = 140
0
0.964
325
0.978
0.993
1.007
1.022
1.036
CURRENT-LIMIT TRIP THRESHOLD (V)
-40
-15
10
35
TEMPERATURE (°C)
60
85
0
326.7
333.5
340.3
347.2
354.0
360.8
SWITCHING FREQUENCY (kHz)
_______________________________________________________________________________________
5
MAX15000/MAX15001
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.)
PROPAGATION DELAY FROM
CURRENT-LIMIT COMPARATOR
INPUT TO NDRV vs. TEMPERATURE
MAX15000A
6
MAX15000 toc14
60
MAX15000 toc13
5
UVLO/EN RISING
100
UVLO DELAY (ms)
55
tPDCS (ns)
50
4
3
2
45
206µs
1
40
10
1
10
100
0
-40
1000
UVLO/EN FALLING
-15
10
35
85
60
-40
-15
10
35
TEMPERATURE (°C)
TEMPERATURE (°C)
UVLO/EN TO UFLG PROPAGATION DELAY
vs. TEMPERATURE
REFERENCE VOLTAGE
vs. TEMPERATURE
INPUT CURRENT
vs. IN VOLTAGE
3
2
UVLO/EN FALLING
1.231
UVLO/EN = 1.4V
NDRV SWITCHING AT 350kHz
1.76
INPUT CURRENT (mA)
UVLO/EN RISING
1.230
1.229
1.60
1.228
-40
-15
10
35
85
60
-40
-15
TEMPERATURE (°C)
10
35
60
11
12
13
14
15
16
IN VOLTAGE (V)
TEMPERATURE (°C)
NDRV LOW OUTPUT IMPEDANCE
vs. TEMPERATURE
2.4
MAX15000 toc19
27.0
IIN = 2mA
26.6
VIN = 24V
SINKING 100mA
2.2
26.4
2.0
26.2
RON (Ω)
INPUT CLAMP VOLTAGE (V)
10
85
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
26.8
1.68
1.64
1
0
1.72
MAX15000 toc20
4
VIN = 12V
REFERENCE VOLTAGE (V)
5
1.80
MAX15000 toc17
1.232
MAX15000 toc16
6
26.0
1.8
25.8
1.6
25.6
25.4
1.4
25.2
25.0
1.2
-40
-20
0
20
40
TEMPERATURE (°C)
6
60
85
60
TIMING RESISTOR (kΩ)
MAX15000 toc18
SWITCHING FREQUENCY (kHz)
1000
UVLO/EN TO NDRV PROPAGATION DELAY
vs. TEMPERATURE
MAX15000 toc15
SWITCHING FREQUENCY
vs. TIMING RESISTOR
UVLO DELAY (µs)
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
80
-40
-15
10
35
60
TEMPERATURE (°C)
_______________________________________________________________________________________
85
17
18
19
Current-Mode PWM Controllers with
Programmable Switching Frequency
ERROR AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY
SOURCING 20mA
80
40
GAIN
40
4.2
3.8
120
80
60
GAIN (dB)
RON (Ω)
4.6
MAX15000 toc22
100
MAX15000 toc21
5.0
20
0
-40
0
-80
PHASE
-20
PHASE (DEGREES)
NDRV HIGH OUTPUT IMPEDANCE
vs. TEMPERATURE
-120
3.4
-40
-160
-60
3.0
-40
-15
10
35
60
85
0.1
1
10 100
-200
1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
TEMPERATURE (°C)
Pin Description
PIN
1
2
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 210µs after the UVLO/EN
voltage falls below 1.17V.
UFLG
Open-Drain Undervoltage Flag Output. UFLG is asserted low as soon as the UVLO/EN voltage falls below its
threshold.
3
FB
4
COMP
Error-Amplifier Inverting Input
5
CS
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.
6
RT
Oscillator Timing Resistor Input. An RC network may be required to reduce jitter (see the Typical Application
Circuit).
7
GND
Ground Connection
8
NDRV
External n-Channel MOSFET Gate Connection
9
VCC
10
IN
Error-Amplifier Output
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.
_______________________________________________________________________________________
7
MAX15000/MAX15001
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
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
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 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.
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
D2
T1
D1
VSUPPLY
VOUT
R1
R2
UVLO/EN
UFLG
FB
C2
COMP
C5
R11
R3
CS
1
2
10
MAX15000
3
9
8
4
7
5
6
IN
R13
VCC
NDRV
Q1
C4
GND
RT
R14
C6
C2
R15
C1
R4
R12
0V
Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage
8
_______________________________________________________________________________________
Current-Mode PWM Controllers with
Programmable Switching Frequency
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.
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 )
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.
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 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 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
_______________________________________________________________________________________
9
MAX15000/MAX15001
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/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
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 210µs 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 =
Figure 2. VIN and VCC During Startup When Using the
MAX15000 in Bootstrapped Mode (Figure 1)
1984
fNDRV
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%)
1.17V (typ)
VUVLO/EN
Hi-Z
VUFLG
LOW
3µs
VNDRV
0.6µs
LOW
NDRV SWITCHING
SHUTDOWN
SHUTDOWN
tEXTR
3ms
tEXTF
210µs
Figure 3. UVLO/EN and UFLG Operation Timing
10
______________________________________________________________________________________
Current-Mode PWM Controllers with
Programmable Switching Frequency
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 =
1010
for the MAX15000A / MAX15001A.
2fSW
R12 =
1010
for the MAX15000B / MAX15001B.
4fSW
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:
1
R15 = 88.9 × (R12) 4
For example, if R12 is 4kΩ, R15 becomes 707Ω.
MAX15000 fig04
VOUT
2V/div
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 VD6
and VD2 are the diode drops at the respective outputs.
______________________________________________________________________________________
11
MAX15000/MAX15001
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/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
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:
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
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.
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 (90µA) 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
12
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)
= 2.24µF
12V
Choose a 2.2µF 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 (90µA max).
For example:
(24V)(2.2µF)
= 0.105mA
(500ms)
(36V) − (12V)
R1 ≅
= 123.07kΩ
(0.105mA) + (90µA)
IC1 =
Choose a 120kΩ standard value.
______________________________________________________________________________________
Current-Mode PWM Controllers with
Programmable Switching Frequency
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.
D1
T1
D2
VOUT
VIN
C4
R1
R2
UFLG
R8
IN
U2
OPTO
TRANS.
VCC
MAX15000A
R9
Q1
NDRV
U1
U2
OPTO LED
CS
C3
R7
C1
GND
COMP
U3
TL431
R5
FB
UVLO/EN
RT
R4
R10
C6
R6
C2
R3
R12
R15
Figure 5. Secondary-Side Regulated, Isolated Power Supply
______________________________________________________________________________________
13
MAX15000/MAX15001
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.
FB_P
IN
D8
R6
33kΩ
36V TO 72V +VIN
+VIN
D6
C16
1µF
35V
C12
15µF
35V
R7
1.2kΩ
15V/100mA
C5
47µF
25V
10 12T
15T
4
C15
1µF
D5
SGND
8
3
R8
OPEN
28T
35µH
C10
OPEN
C3
68µF
6.3V
5T
2
6
1
FB_P
L1
D1
7
VOUT1
5V/1.5A
C13
1µF
D4
C4
22µF SGND
6.3V
C6
0.0047µF
250VAC
D3
OPEN
R1
22.6kΩ
1%
VOUT2
D2
5 T1 9
D7
OPEN
R12
1.2kΩ
C2
1µF
100V
C1
1µF
100V
-VIN
IN
3
R2
+VIN 2.49kΩ
1%
R9
75kΩ
1%
R3
1.37MΩ
1%
R4
51.1kΩ
L2
FB
IN
10
C9
100pF
4
1
U1
COMP
C14
3900pF
NDRV
MAX15000A
UVLO/EN
CS
8
C11
0.22µF R10
4.7Ω
R11
100Ω
5
9
C7
0.22µF
UFLG
SHDN
2
1
R13
10kΩ
JU1
2
VCC
UFLG
GND
RT
8
N1 IRF7464
4
1
C8
OPEN
C17
OPEN
7
56
2
3
R5
0.600Ω
1%
7
6
R14
14.3kΩ
1%
UFLG_PULL
R15
750Ω
C19
OPEN
C18
0.1µF
NOTE: MOSFET N1 = IR IRF7464.
Figure 6. Primary-Side-Regulated, Dual-Output, Isolated Telecom Power Supply
Primary-Side-Regulated,
Isolated Telecom Power Supply
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).
NO LOAD AT 15V
OUTPUT
VIN+ = 40V
VIN- = 0V
5.5
5.4
MAX15000 fig07
5V OUTPUT LOAD REGULATION
5.6
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.
VOUT (V)
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
5.3
5.2
5.1
5.0
4.9
4.8
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
D1
MAX15000/MAX15001
L1
12V
15V
R2
UFLG
R5
IN
Q1
NDRV
VCC
MAX15001
CS
C4
C3
C1
C2
GND
COMP
R1
FB
UVLO/EN
RT
R6
C6
R3
R12
R15
0V
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
µMAX 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.
______________________________________________________________________________________
15
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
Typical Application Circuit
D2
T1
D1
R5
R2
C4
R1
UVLO/EN
UFLG
FB
C2
+
COMP
36V TO 72V C5
-
R11
R3
CS
1
2
10
MAX15000
3
9
8
4
7
5
6
IN
VCC
NDRV
Q1
GND
RT
R6
C6
C2
R15
16
R12
C1
R4
______________________________________________________________________________________
VOUT
Current-Mode PWM Controllers with
Programmable Switching Frequency
IN
IN
IN
CLAMP
26.1V
VCC
VCC
REGULATOR
DIGITAL
SOFT-START
BOOTSTRAP UVLO
REFERENCE
1.23V
REG_OK
*
VL
(INTERNAL 5.25V
SUPPLY)
21.6V
9.74V
210µs
DELAY
UFLG
UVLO
UVLO/EN
N
1.23V
1.17V
COMP
DRIVER
S
FB
NDRV
Q
ERROR
AMP
R
CPWM
OSCILLATOR
1.4V
CS
GND
VCS
1V
MAX15000
MAX15001
ILIM
RT
Selector Guide
PART
BOOTSTRAP
STARTUP
UVLO
VOLTAGE (V)
MAX DUTY
CYCLE (%)
MAX15000A
Yes
22
MAX15000B
Yes
22
75
MAX15001A*
No
9.5
50
MAX15001B*
No
9.5
75
*MAX15000 ONLY
Chip Information
PROCESS: BiCMOS
50
*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.
______________________________________________________________________________________
17
MAX15000/MAX15001
Functional Diagram
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.)
e
10LUMAX.EPS
MAX15000/MAX15001
Current-Mode PWM Controllers with
Programmable Switching Frequency
4X S
10
10
INCHES
H
Ø0.50±0.1
0.6±0.1
1
1
0.6±0.1
BOTTOM VIEW
TOP VIEW
D2
MILLIMETERS
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
α
0°
6°
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°
E2
GAGE PLANE
A2
c
A
b
A1
α
E1
L
D1
L1
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0061
REV.
1
1
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
© 2006 Maxim Integrated Products
Heaney
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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