MAX5021 データシートの表示（PDF） - Maxim Integrated
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MAX5021 Datasheet PDF : 11 Pages
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Current-Mode PWM Controllers for Isolated
Power Supplies
T1
RS
VOUT
C2
VCC
VIN
C3
MAX5022
OPTO
NDRV
GND
CS
-36VDC TO -72VDC IN
Figure 4. -48VDC Input to +5V Output
WARNING! DANGEROUS AND LETHAL VOLTAGES
ARE PRESENT IN OFF-LINE CIRCUITS! USE
EXTREME CAUTION IN THE CONSTRUCTION,
TESTING, AND USE OF OFF-LINE CIRCUITS.
Isolated Telecom Power Supply
Figure 4 shows a -48VDC telecom power supply capa-
ble of generating an isolated +5V output.
Layout Recommendations
All printed circuit board traces carrying switching cur-
rents must be kept as short as possible, and the cur-
rent loops they form must be minimized. The pins of the
SOT23 package have been placed to allow simple
interfacing to the external MOSFET. The order of these
pins directly corresponds to the order of a TO-220 or
similar package MOSFET.
For universal AC input design all applicable safety reg-
ulations must be followed. Off-line power supplies may
require UL, VDE, and other similar agency approvals.
These agencies can be contacted for the latest layout
and component rules.
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 cur-
rent often form high di/dt loops. Similarly the heatsink of
the MOSFET presents a dv/dt source, thus the surface
area of the heatsink must be minimized as much
as possible.
To achieve best performance, a star ground connection
is recommended to avoid ground loops. For example,
the ground returns for the power-line input filter, power
MOSFET switch, and sense resistor should be routed
separately through wide copper traces to meet at a sin-
gle system ground connection.
Chip Information
TRANSISTOR COUNT: 519
PROCESS: BiCMOS
8 _______________________________________________________________________________________
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