19-2066; Rev 1; 9/01
AILABLE
ION KIT AV
EVALUAT
Current-Mode PWM Controllers for Isolated
Power Supplies
General Description
The MAX5021/MAX5022 current-mode PWM controllers
contain all the control circuitry required for the design
of wide input voltage range isolated power supplies.
These devices are well suited for use in universal input
(85VAC to 265VAC) off-line or telecom (-36VDC to
-72VDC) power supplies.
An undervoltage lockout (UVLO) circuit with large hys-
teresis coupled with low startup and operating current
reduce power dissipation in the startup resistor and
allow use of ceramic bypass capacitors. The 262kHz
switching frequency is internally trimmed to ±12%
accuracy; this allows the optimization of the magnetic
and filter components resulting in compact, cost-effec-
tive power supplies. The MAX5021 with 50% maximum
duty cycle and MAX5022 with 75% maximum duty
cycle are recommended for forward converters and fly-
back converters, respectively. The MAX5021/MAX5022
are available in 6-pin SOT23, 8-pin µMAX, and 8-pin
DIP packages and are rated for operation over the
-40°C to +85°C temperature range.
o
50µA Typical Startup Current
o
1.2mA Typical Operating Current
o
Large UVLO Hysteresis of 14V
o
Fixed Switching Frequency of 262kHz ±12%
o
50% Maximum Duty Cycle Limit (MAX5021)
o
75% Maximum Duty Cycle Limit (MAX5022)
o
60ns Cycle-by-Cycle Current-Limit Response
Time
Features
o
Available in a Tiny 6-Pin SOT23 Package
MAX5021/MAX5022
Ordering Information
PART
MAX5021EUT
MAX5021EUA
MAX5021EPA
MAX5022EUT
MAX5022EUA
MAX5022EPA
MAX
DUTY
CYCLE
50%
50%
50%
75%
75%
75%
TEMP.
RANGE
PIN-
TOP
PACKAGE MARK
Applications
Universal Off-Line Power Supplies
Standby Power Supplies
Isolated Power Supplies
Isolated Telecom Power Supplies
Mobile Phone Chargers
-40°C to +85°C 6 SOT23-6 AASQ
-40°C to +85°C 8
µMAX
-40°C to +85°C 8 PDIP
-40°C to +85°C 6 SOT23-6
-40°C to +85°C 8
µMAX
-40°C to +85°C 8 PDIP
—
—
AASR
—
—
WARNING: The MAX5021/MAX5022 are designed to work
with high voltages. Exercise caution!
Typical Operating Circuit
V
SUPPLY
Pin Configuration
TOP VIEW
CS
1
6
OPTO OPTO
1
V
IN
2
5
V
IN
V
CC
3
8
CS
GND
NDRV
N.C.
V
OUT
GND
2
V
CC
V
IN
MAX5021
MAX5022
MAX5021
MAX5022
7
6
5
MAX5021
MAX5022
OPTO
NDRV
NDRV
3
4
V
CC
N.C.
4
SOT23
GND
CS
PDIP/µMAX
________________________________________________________________
Maxim Integrated Products
1
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.
Current-Mode PWM Controllers for Isolated
Power Supplies
MAX5021/MAX5022
ABSOLUTE MAXIMUM RATINGS
V
IN
to GND .............................................................-0.3V to +30V
V
CC
to GND ............................................................-0.3V to +13V
NDRV to GND.............................................-0.3V to (V
CC
+ 0.3V)
CS, OPTO to GND ....................................................-0.3V to +6V
NDRV Short-Circuit to GND........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C).............696mW
8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW
8-Pin PDIP (derate 9.1mW/°C above +70°C)................727mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +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
(V
IN
= +11V to +28V, V
CS
= 0, OPTO is unconnected, 10nF bypass capacitors at V
IN
and V
CC
, NDRV unconnected, T
A
= -40°C to
+85°C, unless otherwise noted. Typical values are at V
IN
= +12V, T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Undervoltage Lockout Wakeup
Level
Undervoltage Lockout Shutdown
Level
V
IN
Supply Current at Startup
V
IN
Range
Undervoltage Lockout
Propagation Delay
INTERNAL SUPPLY
V
CC
Regulator Set Point
V
IN
Supply Current after Startup
GATE DRIVER
Driver Output Impedance
Driver Peak Sink Current
Driver Peak Source Current
PWM COMPARATOR
Comparator Offset Voltage
CS Input Bias Current
Propagation Delay from
Comparator Input to NDRV
Minimum On-Time
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold
Current-Limit Propagation Delay
from Comparator Input to NDRV
V
CS
T
CL
25mV overdrive
540
600
60
660
mV
ns
VO
PWM
I
CS
T
PWM
T
ON(MIN)
25mV overdrive
V
OPTO
- V
CS
600
-2
60
150
750
900
+2
mV
µA
ns
ns
R
ON(LOW)
I
SINK
I
SOURCE
Measured at NDRV sinking 5mA
10
20
250
150
20
40
R
ON(HIGH)
Measured at NDRV sourcing 5mA
Ω
mA
mA
V
CCSP
I
IN
V
IN
= +11V to +28V, sourcing 1µA to 5mA
from V
CC
V
IN
= +28V, OPTO connected to GND
V
IN
= +28V, OPTO unconnected (Note 2)
7.0
0.9
0.4
10.5
2.43
V
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UNDERVOLTAGE LOCKOUT/STARTUP
V
UVR
V
UVF
I
START
V
IN
T
UVR
T
UVF
V
IN
steps up from +9V to +26V
V
IN
steps down from +26V to +9V
V
IN
rising
V
IN
falling
V
IN
= +22V
11
5
1
22
9.3
24
10
50
26
10.9
85
28
V
V
µA
V
µs
2
_______________________________________________________________________________________
Current-Mode PWM Controllers for Isolated
Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= +11V to +28V, V
CS
= 0, OPTO is unconnected, 10nF bypass capacitors at V
IN
and V
CC
, NDRV unconnected, T
A
= -40°C to
+85°C, unless otherwise noted. Typical values are at V
IN
= +12V, T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
OPTO INPUT
OPTO Pullup Voltage
OPTO Pullup Resistance
V
OPTO
R
OPTO
OPTO sourcing 10µA
4.5
6.2
5.5
7.9
V
kΩ
f
SW
D
MAX
MAX5021
MAX5022
230
262
50
75
290
51
76
kHz
%
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX5021/MAX5022
Note 1:
All devices are 100% tested at T
A
= +25°C. All limits over temperature are guaranteed by characterization.
Note 2:
This minimum current after startup is a safeguard that prevents the V
IN
pin voltage from rising in the event
that OPTO and NDRV become unconnected.
Typical Operating Characteristics
(V
IN
= 15V, T
A
= +25°C, unless otherwise noted.)
UNDERVOLTAGE LOCKOUT
vs. TEMPERATURE
MAX5021/22 toc01
UNDERVOLTAGE LOCKOUT
vs. TEMPERATURE
MAX5021/22 toc02
STARTUP CURRENT
vs. TEMPERATURE
MAX5021/22 toc03
24.3
V
IN
RISING
UNDERVOLTAGE LOCKOUT (V)
24.2
10.2
V
IN
FALLING
10.1
53
52
STARTUP CURRENT (µA)
51
50
49
48
V
IN
= 23.0V
24.1
UNDERVOLTAGE LOCKOUT (V)
10.0
24.0
9.9
23.9
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
9.8
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
47
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
3
Current-Mode PWM Controllers for Isolated
Power Supplies
MAX5021/MAX5022
Typical Operating Characteristics (continued)
(V
IN
= 15V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX5021/22 toc04
MAXIMUM V
CC
vs. TEMPERATURE
MAX5021/22 toc05
MINIMUM V
CC
vs. TEMPERATURE
V
IN
= 10.8V
5mA LOAD ON V
CC
V
CS
= 0
OPTO = UNCONNECTED
MAX5021/22 toc06
1.60
V
IN
= 28.0V
V
OPTO
= V
CS
= 0
SUPPLY CURRENT (mA)
1.55
9.15
8.30
8.20
MINIMUM V
CC
(V)
8.10
8.00
7.90
7.80
7.70
9.12
MAXIMUM V
CC
(V)
9.09
1.50
9.06
V
IN
= 28.0V
V
CS
= 0
OPTO = UNCONNECTED
-40
-20
0
20
40
60
80
1.45
9.03
1.40
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
9.00
TEMPERATURE (°C)
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
CURRENT SENSE THRESHOLD
vs. TEMPERATURE
MAX5021/22 toc07
CURRENT SENSE
THRESHOLD
MAX5021/22 toc08
OSCILLATOR FREQUENCY
vs. TEMPERATURE
TOTAL NUMBER
OF DEVICES = 50
+3σ
MEAN
MAX5021/22 toc09
640
CURRENT SENSE THRESHOLD (mV)
630
620
610
600
590
580
570
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
-3σ
TOTAL NUMBER OF
DEVICES = 50
+3σ
MEAN
25
TOTAL NUMBER
OF DEVICES = 200
280
OSCILLATOR FREQUENCY (kHz)
275
270
265
260
255
250
-3σ
20
FREQUENCY (%)
15
10
5
0
540
560
580
600
620
640
660
CURRENT SENSE THRESHOLD (mV)
245
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
OSCILLATOR FREQUENCY
MAX5021/22 toc10
CURRENT SENSE DELAY
vs. TEMPERATURE
MAX5021/22 toc11
UNDERVOLTAGE LOCKOUT
DELAY vs. TEMPERATURE
UNDERVOLTAGE LOCKOUT DELAY (µs)
MAX5021/22 toc12
25
TOTAL NUMBER
OF DEVICES = 200
20
FREQUENCY (%)
75
6
5
V
IN
RISING
4
3
2
V
IN
FALLING
1
0
15
CURRENT SENSE DELAY (ns)
70
65
10
60
5
55
0
230
240
250
260
270
280
290
OSCILLATOR FREQUENCY (kHz)
50
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Current-Mode PWM Controllers for Isolated
Power Supplies
Pin Description
PIN
SOT23
1
2
3
4
PDIP
µMAX
8
7
6
3
NAME
FUNCTION
Current Sense Connection for PWM Regulation and Overcurrent Protection. The current-limit
comparator threshold is internally set to 0.6V.
Power-Supply Ground
External N-Channel MOSFET Gate Connection
Gate Drive Supply. Internally regulated down from V
IN
. Decouple with a 10nF or larger
capacitor to GND.
IC Supply. Decouple with a 10nF or larger capacitor to GND. Connect a startup resistor
(R
s
) from the input supply line to V
IN
. Connect to bias winding through diode rectifier.
See
Typical Operating Circuit.
Optocoupler Transistor Collector Connection. Connect emitter of optocoupler to GND.
The OPTO has an internal pullup resistor with a typical value of 6.2kΩ.
No Connection. Do not make connections to these pins.
MAX5021/MAX5022
CS
GND
NDRV
V
CC
5
2
V
IN
6
—
1
4, 5
OPTO
N.C.
Detailed Description
The MAX5021/MAX5022 are current-mode PWM con-
trollers that have been specifically designed for use in
isolated power supplies. An undervoltage lockout cir-
cuit (UVLO) with a large hysteresis (14V) along with
very low startup and operating current result in high-
efficiency, universal input power supplies. Both devices
can be used in power supplies capable of operating
from a universal 85VAC to 265VAC line or the telecom
voltage range of -36VDC to -72VDC.
Power supplies designed with these devices use a
high-value startup resistor, R
S
, (series combination of
R
1
and R
2
) that charges a reservoir capacitor, C2 (see
Figure 1). During this initial period while the voltage is
less than the UVLO start threshold, the IC typically con-
sumes only 50µA of quiescent current. This low startup
current and the large UVLO hysteresis combined with
the use of a ceramic capacitor C2 keeps the power dis-
sipation in R
S
to less than 1/4W even at the high end of
the universal AC input voltage (265VAC).
The MAX5021/MAX5022 include a cycle-by-cycle cur-
rent limit which turns off the gate drive to the external
MOSFET during an overcurrent condition. If the output
on the secondary side of transformer T1 is shorted, the
tertiary winding voltage will drop below the 10V thresh-
old causing the UVLO circuit to turn off the gate drive to
the external power MOSFET, thus re-initiating the start-
up sequence.
Startup
Figure 2 shows the voltages on V
IN
and V
CC
during
startup. Initially, both V
IN
and V
CC
are 0V. After the line
voltage is applied, C2 charges through the startup
resistor, R
S
, to an intermediate voltage at which point
the internal reference and regulator begin charging C3
(see Figure 1). The bias current consumed by the
device during this period is only 50µA; the remaining
input current charges C2 and C3. Charging of C3 stops
when the V
CC
voltage reaches approximately 9.5V,
while the voltage across C2 continues rising until it
reaches the wakeup level of 24V. Once V
IN
exceeds
the UVLO threshold, NDRV begins switching the
MOSFET, transferring energy to the secondary and ter-
tiary outputs. If the voltage on the tertiary output builds
to higher than 10V (UVLO lower threshold), then startup
has been accomplished and sustained operation
will commence.
If V
IN
drops below 10V before startup is complete, then
the IC goes back into UVLO. In this case, increase the
value of C2 and/or use a MOSFET with a lower gate-
charge requirement.
Startup Time Considerations
The V
IN
bypass capacitor C2 supplies current immediate-
ly after wakeup. The size of C2 will determine the number
of cycles available for startup. Large values for C2 will
increase the startup time, but will also supply more gate
charge, allowing for more cycles after wakeup. If the
value of C2 is too small, V
IN
will drop below 10V because
5
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