ATW28XXD Series
ATW28XXD Block Diagram
3
4
5
+V out
R eturn
-Vout
E M I
Filter
1
+Input
Drive 1
Drive 2
8
E nable
Pulse W idth
M odulator
Error Amp
Reference
FB
2
&
S ync
Input
R eturn
10
Application Information
Inhibit Function
Connecting the inhibit input (Pin 8) to input common (Pin 10)
will cause the converter to shut down. It is recommended
that the inhibit pin be driven by an open collector device
capable of sinking at least 400µA of current. The open cir-
cuit voltage of the inhibit input is 11.5 ±1 VDC.
The user should be aware that the synchronization sys-
tem is fail-safe; that is, the slaves will continue operating
should the master frequency be interrupted for any rea-
son. The layout must be such that the synchronization
output (pin 2) of the master device is connected to the
synchronization input (pin 2) of each slave device. It is
advisable to keep this run short to minimize the possibil-
ity of radiating the 250KHz switching frequency.
EMI Filter
An optional external EMI filter (AFC461) is available that will
reduce the input ripple current to levels below the limits
imposed by MIL-STD-461B CEO3.
The appropriate parts must be ordered to utilize this fea-
ture. After selecting the converters required for the sys-
tem, a ‘MSTR’ suffix is added for the master converter
part number and a ‘SLV’ suffix is added for slave part
number. See Part Number section.
Device Synchronization
Whenever multiple DC/DC converters are utilized in a single
system, significant low frequency noise may be generated
due to the slight differences in the switching frequencies of
the converters (beat frequency noise). Because of the low
frequency nature of this noise (typically less than 10KHz), it
is difficult to filter out and may interfere with proper operation
of sensitive systems (communications, radar or telemetry).
Advanced Analog offers an option, which allows synchroni-
zation of multiple AHE/ATW type converters, thus eliminat-
ing this type of noise.
Typical Synchronization Connection
+
In
Output
Return
+
In
Output
Return
A FC 461
or
A FV461
Case
A TW 28xxS
M STR
Return
Return
S ystem
B us
+
In
Output
Return
Output
A TW 28xxD
or O ther
C om patable
SLV
To take advantage of this capability, the system designer
must assign one of the converters as the master. Then, by
definition, the remaining converters become slaves and will
operate at the masters’ switching frequency.
Case
Return
Output
Return
+
In
Case
A TW 28xxD
SLV
Output
Return
6
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