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PDF AFL270XXD Data sheet ( Hoja de datos )
| Número de pieza | AFL270XXD | |
| Descripción | ADVANCED ANALOG HIGH RELIABILITY HYBRID DC/DC CONVERTERS | |
| Fabricantes | International Rectifier | |
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PD - 94461B
ADVANCED ANALOG
HIGH RELIABILITY
HYBRID DC/DC CONVERTERS
Description
The AFL Series of DC/DC converters feature high power
density with no derating over the full military tempera-
ture range. This series is offered as part of a complete
family of converters providing single and dual output
voltages and operating from nominal +28 or +270 volt
inputs with output power ranging from 80 to 120 watts.
For applications requiring higher output power, indi-
vidual converters can be operated in parallel. The inter-
nal current sharing circuits assure equal current distri-
bution among the paralleled converters. This series in-
corporates Advanced Analog’s proprietary magnetic
pulse feedback technology providing optimum dynamic
line and load regulation response. This feedback sys-
tem samples the output voltage at the pulse width modu-
lator fixed clock frequency, nominally 550 KHz. Multiple
converters can be synchronized to a system clock in the
500 KHz to 700 KHz range or to the synchronization
output of one converter. Undervoltage lockout, primary
and secondary referenced inhibit, soft-start and load
fault protection are provided on all models.
These converters are hermetically packaged in two en-
closure variations, utilizing copper core pins to mini-
mize resistive DC losses. Three lead styles are avail-
able, each fabricated with Advanced Analog’s rugged
ceramic lead-to-package seal assuring long term
hermeticity in the most harsh environments.
Manufactured in a facility fully qualified to MIL-PRF-
38534, these converters are available in four screening
grades to satisfy a wide range of requirements. The CH
grade is fully compliant to the requirements of MIL-H-
38534 for class H. The HB grade is processed and
screened to the class H requirement, but may not nec-
essarily meet all of the other MIL-PRF-38534 require-
ments, e.g., element evaluation and Periodic Inspection
(P.I.) not required. Both grades are tested to meet the
complete group “A” test specification over the full mili-
tary temperature range without output power deration.
Two grades with more limited screening are also avail-
www.irf.com
AFL270XXD SERIES
270V Input, Dual Output
AFL
Features
n 160 To 400 Volt Input Range
n ±5, ±12, and ±15 Volts Outputs Available
n High Power Density - up to 70 W / in3
n Up To 100 Watt Output Power
n Parallel Operation with Power Sharing
n Low Profile (0.380") Seam Welded Package
n Ceramic Feedthru Copper Core Pins
n High Efficiency - to 87%
n Full Military Temperature Range
n Continuous Short Circuit and Overload
Protection
n Output Voltage Trim
n Primary and Secondary Referenced
Inhibit Functions
n Line Rejection > 60 dB - DC to 50KHz
n External Synchronization Port
n Fault Tolerant Design
n Single Output Versions Available
n Standard Military Drawings Available
able for use in less demanding applications. Varia-
tions in electrical, mechanical and screening can
be accommodated. Contact Advanced Analog for
special requirements.
1
09/11/02
1 page  
DC Input 1
Enable 1 4
Sync Output 5
Sync Input 6
Case 3
AFL270XXD Series
AFL270XXD Circuit Description
Figure I. AFL Dual Output Block Diagram
Input
Filter
Output
Filter
7 + Output
Primary
Bias Supply
Current
Sense
8 Output Return
Output
Filter
9 -Output
Control
Error
Amp
& Ref
Share
Amplifier
11 Share
12 Enable 2
10 Trim
Input Return 2
Circuit Operation and Application Information
The AFL series of converters employ a forward switched
mode converter topology. (refer to Figure I.) Operation of
the device is initiated when a DC voltage whose magnitude
is within the specified input limits is applied between pins 1
and 2. If pins 4 and 12 are enabled (at a logical 1 or open)
the primary bias supply will begin generating a regulated
housekeeping voltage bringing the circuitry on the primary
side of the converter to life. Two power MOSFETs used to
chop the DC input voltage into a high frequency square
wave, apply this chopped voltage to the power transformer.
As this switching is initiated, a voltage is impressed on a
second winding of the power transformer which is then
rectified and applied to the primary bias supply. When this
occurs, the input voltage is excluded from the bias voltage
generator and the primary bias voltage becomes internally
generated.
The switched voltage impressed on the secondary output
transformer windings is rectified and filtered to provide the
positive and negative converter output voltages. An error
amplifier on the secondary side compares the positive out-
put voltage to a precision reference and generates an error
signal proportional to the difference. This error signal is
magnetically coupled through the feedback transformer into
the control section of the converter varying the pulse width
of the square wave signal driving the MOSFETs, narrowing
the pulse width if the output voltage is too high and widening
it if it is too low. These pulse width variations provide the
necessary corrections to regulate the magnitude of output
voltage within its’ specified limits.
Because the primary portion of the circuit is coupled to the
secondary side with magnetic elements, full isolation from
input to output is maintained.
Although incorporating several sophisticated and useful
ancilliary features, basic operation of the AFL270XXDseries
can be initiated by simply applying an input voltage to pins 1
and 2 and connecting the appropriate loads between pins 7,
8, and 9. Of course, operation of any converter with high
power density should not be attempted before secure at-
tachment to an appropriate heat dissipator. (See Thermal
Considerations, page 7)
Inhibiting Converter Output
As an alternative to application and removal of the DC volt-
age to the input, the user can control the converter output
by providing TTL compatible, positive logic signals to either
of two enable pins (pin 4 or 12). The distinction between
these two signal ports is that enable 1 (pin 4) is referenced
to the input return (pin 2) while enable 2 (pin 12) is refer-
enced to the output return (pin 8). Thus, the user has
access to an inhibit function on either side of the isolation
barrier. Each port is internally pulled “high” so that when not
used, an open connection on both enable pins permits nor-
mal converter operation. When their use is desired, a logi-
cal “low” on either port will shut the converter down.
Figure II. Enable Input Equivalent Circuit
+5.6V
Pin 4 or
Pin 12
1N4148
100K
290K
Disable
2N3904
Pin 2 or
Pin 8
150K
www.irf.com
5
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