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PDF MAX5022 Data sheet ( Hoja de datos )
| Número de pieza | MAX5022 | |
| Descripción | Current-Mode PWM Controllers for Isolated Power Supplies | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2066; Rev 1; 9/01
EVALUATION
KIT
AVAILABLE
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.
Applications
Universal Off-Line Power Supplies
Standby Power Supplies
Isolated Power Supplies
Isolated Telecom Power Supplies
Mobile Phone Chargers
Features
o Available in a Tiny 6-Pin SOT23 Package
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
Ordering Information
PART
MAX
DUTY
CYCLE
TEMP.
RANGE
PIN-
TOP
PACKAGE MARK
MAX5021EUT
MAX5021EUA
MAX5021EPA
MAX5022EUT
MAX5022EUA
MAX5022EPA
50%
50%
50%
75%
75%
75%
-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 AASR
-40°C to +85°C 8 µMAX
—
-40°C to +85°C 8 PDIP
—
WARNING: The MAX5021/MAX5022 are designed to work
with high voltages. Exercise caution!
Typical Operating Circuit
VSUPPLY
VOUT
VCC VIN
MAX5021
MAX5022
OPTO
NDRV
GND CS
Pin Configuration
TOP VIEW
CS 1
GND 2
NDRV 3
MAX5021
MAX5022
6 OPTO OPTO 1
5 VIN
VIN 2
VCC 3
N.C. 4
4 VCC
MAX5021
MAX5022
8 CS
7 GND
6 NDRV
5 N.C.
SOT23
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.
1 page  
Current-Mode PWM Controllers for Isolated
Power Supplies
PIN
SOT23
PDIP
µMAX
18
27
36
43
52
61
— 4, 5
Pin Description
NAME
FUNCTION
CS
GND
NDRV
VCC
VIN
OPTO
N.C.
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 VIN. Decouple with a 10nF or larger
capacitor to GND.
IC Supply. Decouple with a 10nF or larger capacitor to GND. Connect a startup resistor
(Rs) from the input supply line to VIN. 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.
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, RS, (series combination of
R1 and R2) 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 RS 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 VIN and VCC during
startup. Initially, both VIN and VCC are 0V. After the line
voltage is applied, C2 charges through the startup
resistor, RS, 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 VCC voltage reaches approximately 9.5V,
while the voltage across C2 continues rising until it
reaches the wakeup level of 24V. Once VIN 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 VIN 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 VIN 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, VIN will drop below 10V because
_______________________________________________________________________________________ 5
5 Page 
Current-Mode PWM Controllers for Isolated
Power Supplies
Package Information (continued)
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet MAX5022.PDF ] | |
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