ATR2800D_15 Datasheet, PDF (6/8 Pages) International Rectifier – HYBRID - HIGH RELIABILITY DC-DC CONVERTER

ATR28XXD Series
1
+Input
EMI
Filter
Block Diagram
2
Inhibit Input
8
Case
9
Sync
Primary
Housekeeping
Supply
Drive
Pulse Width
Modulator ^FB
CS
3 +Vout
Regulator
4
Output
Return
5 -Vout
Error
Amp &
Ref
10
Input Return
Application Information
Inhibit Function
Connecting the inhibit input (Pin 2) 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
circuit voltage of the inhibit input is 11.5 ±1.0VDC.
EMI Filter
An EMI filter (AFC461), available as an option, will reduce
the input ripple current to levels below the limits imposed by
MIL-STD-461B CEO3.
Thermal Management
Assuming that there is no forced air flow, the package
temperature rise above ambient (∆T) may be calculated
using the following expression:
∆Τ = 80 A ^–0.7 P_d ^0.85 (°C)
(1)
where A = the effective surface area in square inhes
(in-cluding heat sink if used), P_d = power dissipation in watts.
The total surface area of the ATR standard package is
7.34 square inches. If a worse case full load efficiency of
78% is assumed, then the case temperature rise can be
calculated as follows:
Device Synchronization
Whenever multiple DC/DC converters are utilized in a single
system, significant low frequency noise may be generated
due to slight difference 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).
The International Rectifier ATR28XX converters provide a
synchronizing input permitting synchronization of multiple
converters to the frequency of the users system clock,
thereby minimizing this type of noise.
6
P_d
=
P_OUT
⎡
⎢⎣
1
Eff
−
1_{⎥⎦⎤}
=
30_{⎢⎣⎡}
1
78
−
1_{⎥⎦⎤}
=
8.5W
and
∆Τ = 80 (7.34) ^–0.7 (8.5) ^0.85 = 122°C
Hence, if T_AMBIENT = +25°C, the DC/DC converter case
temperature will be approximately 147°C if no heat sink
or air flow is provided.
To calculate the heat sink area required to maintain a
specific case temperature rise, equation (1) may be
manipulated as follows:
A_HEATSINK
=
⎡ _∆T
⎢
⎢⎣
80P_d
0.85
⎤ ^−1.43
⎥
⎥⎦
−
A_PKG
As an example, if it is desired to limit the case
temperature rise to a maximum of 50°C above ambient,
the required effective heat sink area is:
A_HEATSINK
=
⎡
⎢
⎣
50
80(8.5)
0.85
⎤
⎥
⎦
−1.43
− 7.34 = 19.1in²
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