IRF AHP2808S High reliability hybrid dc/dc converter Datasheet

PD-97388
AHP28XXS SERIES
28V Input, Single Output
HIGH RELIABILITY
HYBRID DC/DC CONVERTERS
Description
The AHP Series of DC/DC converters feature high power
density without derating over the full military temperature
range. This series is offered as lower cost alternatives to
the legendary AFL series with improved performance
for new design applications. The AHPs are form, fit and
functional replacement to the AFL series. The new AHP
series offers a full compliment of single and dual output
voltages operating from nominal +28 or +270 volt inputs
with output power ranging from 66 to 120 watts. For
applications requiring higher output power, multiple
converters can be operated in parallel. The internal
current sharing circuits assure equal current distribution
among the paralleled converters. Same as the AFL, the
AHP series incorporates International Rectifier's
proprietary magnetic pulse feedback technology
providing optimum dynamic line and load regulation
response. This feedback system samples the output
voltage at the pulse width modulator 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. Under-voltage lockout, primary and secondary
referenced inhibit, soft-start and load fault protection are
provided on all models. Also included is input overvoltage protection, a new protection feature unique to
the AHP.
These converters are hermetically packaged in two
enclosure variations, utilizing copper core pins to
minimize resistive DC losses. Three lead styles are
available, each fabricated with International Rectifier’s
rugged ceramic lead-to-package seal assuring long
term hermeticity in harsh environments.
Manufactured in a facility fully qualified to MIL-PRF38534, 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 MILPRF-38534 for class H. The HB grade is fully processed
and screened to the class H requirement, but does not
have material element evaluated to the class H
requirement. Both grades are tested to meet the
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AHP
Features
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16 To 40 Volt Input Range
3.3, 5, 8, 9,12,15 and 28 Volts Outputs Available
High Power Density - up to 84 W / in3
Up To 120 Watt Output Power
Parallel Operation with Stress and Current Sharing
Input Over-Voltage Protection
High Efficiency - to 85%
Continuous Short Circuit and Overload Protection
External Synchronization Port
Remote Sensing Terminals
Primary and Secondary Referenced
Inhibit Functions
Line Rejection > 40 dB - DC to 50KHz
Fault Tolerant Design
Full Military Temperature Range
Ceramic Feedthru Copper Core Pins
Low Profile (0.380") Seam Welded Package
Dual Output Versions Available
complete group “A” test specification over the full
military temperature range without output power
de-rating. Two grades with more limited screening
are also available for use in less demanding
applications. Variations in electrical, mechanical
and screening can be accommodated. Please
contact IR Santa Clara for special requirements.
1
04/16/09
AHP28XXS Series
Specifications
ABSOLUTE MAXIMUM RATINGS
Input Voltage
Soldering Temperature
-0.5V to 50V
300°C for 10 seconds
Case Temperature - Operating
Case Temperature - Storage
-55°C to +125°C
-65°C to +135°C
Static Characteristics -55°C < TCASE < +125°C, 16V< VIN < 40V unless otherwise specified.
Group A
Subgroups
Parameter
Test Conditions
Min
Nom
Max
Unit
16
28
40
V
1
1
1
1
1
1
1
3.27
4.95
7.92
8.91
11.88
14.85
27.72
3.30
5.00
8.00
9.00
12.00
15.00
28.00
3.33
5.05
8.08
9.09
12.12
15.15
28.28
V
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
3.23
4.90
7.84
8.82
11.76
14.70
27.44
INPUT VOLTAGE
Note 6
OUTPUT VOLTAGE
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
VIN = 28V, 100% Load
OUTPUT CURRENT
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
VIN = 16, 28, 40V - Note 6
OUTPUT POWER
Note 6
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
3.37
5.10
8.16
9.18
12.24
15.30
28.56
20
16
10
10
9.0
8.0
4.0
A
66
80
80
90
108
120
112
W
µF
MAXIMUM CAPACITIVE LOAD
Note 1
10,000
OUTPUT VOLTAGE
TEMPERATURE COEFFICIENT
VIN = 28V, 100% Load – Notes 1, 6
-0.015
+0.015
%/°C
-70
-20
+70
+20
mV
mV
-1.0
+1.0
%
OUTPUT VOLTAGE REGULATION
AHP2828S
Line
All Others
Line
Load
OUTPUT RIPPLE VOLTAGE
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
1, 2, 3
1, 2, 3
No Load, 50% Load, 100% Load
VIN = 16, 28, 40V
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
VIN = 16, 28, 40V, 100% Load,
BW = 10MHz
30
30
40
40
45
50
100
mVpp
For Notes to Specifications, refer to page 4
2
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AHP28XXS Series
Static Characteristics (Continued)
Group A
Subgroups
Parameter
INPUT CURRENT
No Load
Inhibit 1
Inhibit 2
INPUT RIPPLE CURRENT
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
1
2, 3
1, 2, 3
1, 2, 3
1,
1,
1,
1,
1,
1,
1,
CURRENT LIMIT POINT
As a percentage of full rated load
LOAD FAULT POWER
DISSIPATION
Overload or Short Circuit
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
1
2
3
1, 2, 3
EFFICIENCY
AHP2803R3S
AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
ENABLE INPUTS (Inhibit Function)
Converter Off
Sink Current
Converter On
Sink Current
SWITCHING FREQUENCY
SYNCHRONIZATION INPUT
Frequency Range
Pulse Amplitude, Hi
Pulse Amplitude, Lo
Pulse Rise Time
Pulse Duty Cycle
ISOLATION
1,
1,
1,
1,
1,
1,
1,
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
1, 2, 3
1, 2, 3
Test Conditions
Min
VIN = 28V
IOUT = 0
Pin 4 Shorted to Pin 2
Pin 12 Shorted to Pin 8
VIN = 28V, 100% Load, BW = 10MHz
VOUT = 90% VNOM, VIN = 28V, Note 5
60
60
60
60
60
60
60
115
105
125
VIN = 28V
VIN = 28V, 100% Load
Logical Low on Pin 4 or Pin 12
Note 1
Logical High on Pin 4 and Pin 12 - Note 9
Note 1
72
78
79
80
80
81
81
2.0
1, 2, 3
1, 2, 3
1, 2, 3
500
2.0
-0.5
Input to Output or Any Pin to Case
(except Pin 3). Test @ 500VDC
DEVICE WEIGHT
Slight Variations with Case Style
MTBF
MIL-HDBK-217F, AIF @ TC = 70°C
550
20
100
mA
mApp
%
33
W
%
0.8
100
50
100
V
µA
V
µA
600
KHz
700
10
0.8
100
80
KHz
V
V
ns
%
MΩ
85
300
Unit
125
115
140
74
81
82
83
84
85
84
-0.5
500
Note 1
Note 1
Max
80
100
5.0
50
1, 2, 3
1
Nom
g
KHrs
For Notes to Specifications, refer to page 4
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3
AHP28XXS Series
Dynamic Characteristics -55°C < TCASE < +125°C, VIN=28V unless otherwise specified.
Group A
Subgroups
LOAD TRANSIENT RESPONSE
Test Conditions
Min
Nom
Max
Unit
Note 2, 8
AHP2803R3S / AHP2805S
AHP2808S
AHP2809S
AHP2812S
AHP2815S
AHP2828S
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-450
450
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-450
450
400
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-500
500
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-500
500
400
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-600
600
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-600
600
400
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-750
750
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-750
750
400
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-750
750
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-750
750
400
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% ⇔ 100%
-1200
1200
200
mV
µs
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 10% ⇔ 50%
-1200
1200
400
mV
µs
-500
500
500
mV
µs
12
10
%
ms
Note 1, 2, 3
LINE TRANSIENT RESPONSE
VIN Step = 16 ⇔ 40V
Amplitude
Recovery
TURN-ON CHARACTERISTICS
Overshoot
Delay
4, 5, 6
4, 5, 6
VIN = 16, 28, 40V. Note 4
Enable 1, 2 on. (Pins 4, 12 high or
open)
LOAD FAULT RECOVERY
Same as Turn On Characteristics.
LINE REJECTION
MIL-STD-461D, CS101, 30Hz to 50KHz
Note 1
0
4.0
40
50
dB
Notes to Specifications:
1.
2.
Parameters not 100% tested but are guaranteed to the limits specified in the table.
Recovery time is measured from the initiation of the transient to where V OUT has returned to within ±1% of
VOUT at 50% load.
Line transient transition time ≥ 100 µs.
Turn-on delay is measured with an input voltage rise time of between 100 and 500 volts per millisecond.
Current limit point is that condition of excess load causing output voltage to drop to 90% of nominal.
Parameter verified as part of another test.
All electrical tests are performed with the remote sense leads connected to the output leads at the load.
Load transient transition time ≥ 10 µs.
Enable inputs internally pulled high. Nominal open circuit voltage ≈ 4.0VDC.
3.
4.
5.
6.
7.
8.
9.
4
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AHP28XXS Series
AHP28XXS Circuit Description
Figure I. AHP Single Output Block Diagram
DC Input 1
Enable 1
Input
Filter
4
Output
Filter
Primary
Bias Supply
7
+Output
10
+Sense
Current
Sense
Sync Output
5
Sync Input 6
Control
FB
Case
3
Error
Amp
& Ref
Share
Amplifier
11 Share
12 Enable 2
Sense
Amplifier
Input Return 2
9
-Sense
8
Output Return
Circuit Operation and Application Information
Inhibiting Converter Output
The AHP 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 pin 4 is 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. A power MOSFET is used to chop the DC
input voltage into a high frequency square wave, applying
this chopped voltage to the power transformer at the nominal
converter switching frequency. Maintaining a DC voltage
within the specified operating range at the input assures
continuous generation of the primary bias voltage.
As an alternative to application and removal of the DC voltage
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 referenced 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 normal
converter operation. When their use is desired, a logical
“low” on either port will shut the converter down.
The switched voltage impressed on the secondary output
transformer winding is rectified and filtered to generate the
converter DC output voltage. An error amplifier on the
secondary side compares the output 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 controller section of the
converter varying the pulse width of the square wave signal
driving the MOSFET, narrowing the width if the output voltage
is too high and widening it if it is too low, thereby regulating
the output voltage.
Remote Sensing
Connection of the + and - sense leads at a remotely located
load permits compensation for excessive resistance
between the converter output and the load when their
physical separation could cause undesirable voltage drop.
This connection allows regulation to the placard voltage at
the point of application. When the remote sensing feature is
not used the sense leads should be connected to their
respective output terminals at the converter. Figure III.
illustrates a typical remotely sensed application.
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Figure II. Enable Input Equivalent Circuit
+5.6V
Pin 4 or
Pin 12
1N4148
100K
Disable
290K
2N3904
200K
Pin 2 or
Pin 8
Internally, these ports differ slightly in their function. In use,
a low on Enable 1 completely shuts down all circuits in the
converter, while a low on Enable 2 shuts down the secondary
side while altering the controller duty cycle to near zero.
Externally, the use of either port is transparent save for
minor differences in standby current. (See specification table).
5
AHP28XXS Series
Synchronization of Multiple Converters
When operating multiple converters, system requirements
often dictate operation of the converters at a common
frequency. To accommodate this requirement, the AHP
series converters provide both a synchronization input and
a synchronization output.
The sync input port permits synchronization of an AHP
connverter to any compatible external frequency source
operating between 500 and 700 KHz. This input signal
should be referenced to the input return and have a 10% to
90% duty cycle. Compatibility requires transition times less
than 100 ns, maximum low level of +0.8 volts and a minimum
high level of +2.0 volts. The sync output of another converter
which has been designated as the master oscillator provides
a convenient frequency source for this mode of operation.
When external synchronization is not required, the sync in
pin should be left open (unconnected )thereby permitting
the converter to operate at its’ own internally set frequency.
The sync output signal is a continuous pulse train set at 550
±50 KHz, with a duty cycle of 15 ±5%. This signal is referenced to the input return and has been tailored to be compatible with the AHP sync input port. Transition times are
less than 100 ns and the low level output impedance is less
than 50 ohms. This signal is active when the DC input
voltage is within the specified operating range and the converter is not inhibited. This output has adequate drive reserve to synchronize at least five additional converters. A
typical connection is illustrated in Figure III.
Figure III. Preferred Connection for Parallel Operation
Power
1
Enable 2
Vin
Input
Share
Rtn
Case
Enable 1
Optional
Synchronization
Connection
12
AHP
+ Sense
- Sense
Sync Out
Return
Sync In
+ Vout
6
7
1
12
Share
Bus
Enable 2
Vin
Rtn
Share
Case
Enable 1
AHP
+ Sense
- Sense
Sync Out
Return
Sync In
+ Vout
6
to Load
7
1
Vin
Enable 2
Rtn
Share
Case
Enable 1
AHP
+ Sense
- Sense
Sync Out
Return
Sync In
+ Vout
6
12
7
(Other Converters)
Parallel Operation-Current and Stress Sharing
Figure III. illustrates the preferred connection scheme for
operation of a set of AHP converters with outputs operating
in parallel. Use of this connection permits equal sharing
among the members of a set whose load current exceeds
the capacity of an individual AHP. An important feature of
6
AHP series operating in the parallel mode is that in addition
to sharing the current, the stress induced by temperature
will also be shared. Thus if one member of a paralleled set
is operating at a higher case temperature, the current it
provides to the load will be reduced as compensation for
the temperature induced stress on that device.
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AHP28XXS Series
When operating in the shared mode, it is important that
symmetry of connection be maintained as an assurance of
optimum load sharing performance. Thus, converter outputs
should be connected to the load with equal lengths of wire of
the same gauge and should be connected to a common
physical point, preferably at the load along with the converter
output and return leads. All converters in a paralleled set
must have their share pins connected together. This
arrangement is diagrammatically illustrated in Figure III.
showing the output and return pins connected at a star
point which is located as close as possible to the load.
As a consequence of the topology utilized in the current
sharing circuit, the share pin may be used for other functions.
In applications requiring only a single converter, the voltage
appearing on the share pin may be used as a “current
monitor”. The share pin open circuit voltage is nominally
+1.00v at no load and increases linearly with increasing
total output current to +2.20v at full load.
Thermal Considerations
Because of the incorporation of many innovative
technological concepts, the AHP series of converters is
capable of providing very high output power from a package
of very small volume. These magnitudes of power density
can only be obtained by combining high circuit efficiency
with effective methods of heat removal from the die junctions.
This requirement has been effectively addressed inside the
device; but when operating at maximum loads, a significant
amount of heat will be generated and this heat must be
conducted away from the case. To maintain the case
temperature at or below the specified maximum of 125°C,
this heat must be transferred by conduction to an
appropriate heat dissipater held in intimate contact with the
converter base-plate.
Because the effectiveness of this heat transfer is dependent
on the intimacy of the baseplate/heatsink interface, it is
strongly recommended that a high thermal conductivity heat
transferring medium is inserted between the baseplate and
heatsink. The material most frequently utilized at the factory
during all testing and burn-in processes is sold under the
trade name of Sil-Pad® 4001 . This particular product is an
insulator but electrically conductive versions are also
available. Use of these materials assures maximum surface
contact with the heat dissipater thereby compensating for
any minor surface variations. While other available types of
heat conductive materials and thermal compounds provide
similar effectiveness, these alternatives are often less
convenient and can be somewhat messy to use.
A conservative aid to estimating the total heat sink surface
area (AHEAT SINK) required to set the maximum case temperature rise (∆T) above ambient temperature is given by
the following expression:
.
⎧ ∆T ⎫ −143
⎬
− 3.0
A HEAT SINK ≈ ⎨
⎩ 80P 0.85 ⎭
where
∆T = Case temperature rise above ambient
⎧ 1
⎫
− 1⎬
P = Device dissipation in Watts = POUT ⎨
⎩ Eff
⎭
As an example, it is desired to maintain the case temperature
of an AHP2815S at ≤ +85°C while operating in an open
area whose ambient temperature is held at a constant
+25°C; then
∆T = 85 - 25 = 60°C
From the Specification Table, the worst case full load
efficiency for this device is 83%; therefore the power
dissipation at full load is given by
⎧ 1
⎫
P = 120 • ⎨
− 1⎬ = 120 • ( 0.205) = 24.6W
⎩ .83 ⎭
and the required heat sink area is
.
⎧
⎫ −143
60
⎬
− 3.0 = 71 in 2
A HEAT SINK = ⎨
⎩ 80 • 24.6 0.85 ⎭
Thus, a total heat sink surface area (including fins, if any) of
71 in2 in this example, would limit case rise to 60°C above
ambient. A flat aluminum plate, 0.25" thick and of
approximate dimension 4" by 9" (36 in 2 per side) would
suffice for this application in a still air environment. Note
that to meet the criteria in this example, both sides of the
plate require unrestricted exposure to the ambient air.
1Sil-Pad is a registered Trade Mark of Bergquist, Minneapolis, MN
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7
AHP28XXS Series
Input Filter
The AHP28XXS series converters incorporate a single stage
LC input filter whose elements dominate the input load
impedance characteristic during the turn-on. The input circuit
is as shown in Figure IV.
Figure IV. Input Filter Circuit
3.5µH
Pin 1
11.2 µfd
⎡
⎤
V NOM
R ADJ = 1000 ⋅ ⎢
⎥
⎣VOUT − V NOM − 0.25 ⎦
For VNOM < VOUT < (VNOM + 0.25V), a resistor is connected
between the +Sense and +Output pins with the –Sense
connected to the output return as shown in Figure VI.
The resistor value (RADJ ) is calculated as follows:
R ADJ =
Pin 2
1000
⎛
⎞
0.25
⎜⎜
− 1⎟⎟
⎝ VOUT − V NOM
⎠
Input Over-Voltage Protection
VNOM = device nominal output voltage
One additional protection feature is incorporated into the
AHP input circuit. It is an input over-voltage protection. The
output will shutdown and restart at approximately 110% of
the maximum rated input voltage. This protection feature is
unique to the AHP.
VOUT = desired output voltage
Undervoltage Lockout
Finding a resistor value for a particular output voltage, is
simply a matter of substituting the desired output voltage
and the nominal device voltage into the equation and solving
for the corresponding resistor value.
A minimum voltage is required at the input of the converter
to initiate operation. This voltage is set to 14.0 ± 0.5 volts.
To preclude the possibility of noise or other variations at the
input falsely initiating and halting converter operation, a
hysteresis of approximately 1.0 volts is incorporated in this
circuit. Thus if the input voltage droops to 13.0 ± 0.5 volts,
the converter will shut down and remain inoperative until the
input voltage returns to ≈14.0 volts.
Output Voltage Adjust
In addition to permitting close voltage regulation of remotely
located loads, it is possible to utilize the converter sense
pins to incrementally increase the output voltage over a
limited range. The adjustments made possible by this
method are intended as a means to “trim” the output to a
voltage setting for some particular application, but are not
intended to create an adjustable output converter. These
output voltage setting variations are obtained by connecting
an appropriate resistor value in the locations as shown in
Figure V or Figure VI depending on the desired output
voltage. The range of adjustment and corresponding range
of resistance values can be determined by use of the
equations presented below.
For (V NOM + 0.25V) < VOUT < (V NOM + 0.5V), a resistor is
connected between the +Sense and –Sense pins with
the –Sense connected to the output return as shown in
Figure V. The resistor value (R ADJ) is calculated as
follows:
8
RADJ = value of the external resistor required to
achieve the desired Vout
Figure V. Connection for VOUT > VNOM+ 0.25V
Enable 2
Share
AHP28XXS
+Sense
RADJ
- Sense
Return
To Load
+Vout
Figure VI. Connection for VNOM< VOUT < (VNOM+ 0.25V)
Enable 2
Share
AHP28XXS
+Sense
RADJ
- Sense
Return
+Vout
To Load
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AHP28XXS Series
Attempts to adjust the output voltage to a value greater than
120% of nominal should be avoided because of the potential
of exceeding internal component stress ratings and
subsequent operation to failure. Under no circumstance
should the external setting resistor be made less than 500Ω.
By remaining within this specified range of values, completely
safe operation fully within normal component derating is
assured.
Examination of the equation relating output voltage and
resistor value reveals a special benefit of the circuit topology
utilized for remote sensing of output voltage in the AHP28XXS
series of converters. It is apparent that as the resistance
increases, the output voltage approaches the nominal set
value of the device. In fact the calculated limiting value of
output voltage as the adjusting resistor becomes very large
is ≅ 250mV above nominal device voltage.
The consequence is that if the +sense connection is
unintentionally broken, an AHP28XXS has a fail-safe output
voltage of Vout + 250mV, where the 250mV is independent
of the nominal output voltage. It can be further demonstrated
that in the event of both the + and - sense connections
being broken, the output will be limited to Vout + 500mV.
This 500mV is also essentially constant independent of the
nominal output voltage. While operation in this condition is
not damaging to the device, not all performance parameters
will be met.
General Application Information
The AHP28XXS series of converters are capable of
providing large transient currents to user loads on demand.
Because the nominal input voltage range in this series is
relatively low, the resulting input current demands will be
correspondingly large. It is important therefore, that the line
impedance be kept very low to prevent steady state and
transient input currents from degrading the supply voltage
between the voltage source and the converter input.
In applications requiring high static currents and large
transients, it is recommended that the input leads be made
of adequate size to minimize resistive losses, and that a
good quality capacitor of approximately100µfd be connected
directly across the input terminals to assure an adequately
low impedance at the input terminals. Table I relates nominal
resistance values and selected wire sizes.
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Table 1. Nominal Resistance of Cu Wire
Wire Size, AWG
Resistance per ft
24 Ga
25.7 mΩ
22 Ga
16.2 mΩ
20 Ga
10.1 mΩ
18 Ga
6.4 mΩ
16 Ga
4.0 mΩ
14 Ga
2.5 mΩ
12 Ga
1.6 mΩ
As an example of the effects of parasitic resistance,
consider an AHP2815S operating at full power of 120 W.
From the specification sheet, this device has a minimum
efficiency of 83% which represents an input power of more
than 145 W. If we consider the case where line voltage is
at its minimum of 16 volts, the steady state input current
necessary for this example will be slightly greater than 9
amperes. If this device were connected to a voltage source
with 10 feet of 20 gauge wire, the round trip (input and
return) would result in 0.2 Ω of resistance and 1.8 volts of
drop from the source to the converter. To assure 16 volts
at the input, a source closer to 18 volts would be required.
In applications using the paralleling option, this drop will be
multiplied by the number of paralleled devices.
By choosing 14 or 16 gauge wire in this example, the
parasitic resistance and resulting voltage drop will be
reduced to 25% or 31% of that with 20 gauge wire.
Another potential problem resulting from parasitically induced
voltage drop on the input lines is with regard to the operation
of the enable 1 port. The minimum and maximum operating
levels required to operate this port are specified with respect
to the input common return line at the converter. If a logic
signal is generated with respect to a ‘common’ that is distant
from the converter, the effects of the voltage drop over the
return line must be considered when establishing the worst
case TTL switching levels. These drops will effectively
impart a shift to the logic levels. In Figure VII, it can be seen
that referred to system ground, the voltage on the input
return pin is given by
eRtn = IRtn • RP
9
AHP28XXS Series
Incorporation of a 100 µfd capacitor at the input terminals
is recommended as compensation for the dynamic effects
of the parasitic resistance of the input cable reacting with
the complex impedance of the converter input, and to
provide an energy reservoir for transient input current
requirements.
Therefore, the logic signal level generated in the system
must be capable of a TTL logic high plus sufficient additional
amplitude to overcome eRtn. When the converter is inhibited,
IRtn diminishes to near zero and eRtn will then be at system
ground.
Figure VII. Problems of Parasitic Resistance in input Leads
(See text)
Rp
esource
Rp
Iin
IRtn
100
µfd
Vin
eRtn
Rtn
Case
System Ground
Enable 1
Sync Out
Sync In
10
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AHP28XXS Series
AHP28XXS Case Outlines
Case X
Case W
Pin Variation of Case Y
3.000
ø 0.128
2.760
0.050
0.050
1
12
0.250
0.250
0.200 Typ
Non-cum
6
7
1.260 1.500
1.000
Ref
1.000
Pin
ø 0.040
0.220
2.500
0.220
Pin
ø 0.040
2.800
2.975 max
0.525
0.238 max
0.42
0.380
Max
0.380
Max
Case Y
Case Z
Pin Variation of Case Y
1.150
0.300
ø 0.140
0.25 typ
0.050
0.050
1
12
0.250
0.250
1.000
Ref
6
1.750
1.000
Ref
0.200 Typ
Non-cum
7
1.500 1.750 2.00
Pin
ø 0.040
0.375
Pin
ø 0.040
0.220
0.220
0.36
2.500
2.800
2.975 max
0.525
0.238 max
0.380
Max
0.380
Max
Tolerances, unless otherwise specified:
.XX
.XXX
=
=
±0.010
±0.005
BERYLLIA WARNING: These converters are hermetically sealed; however they contain BeO substrates and should not be ground or subjected to any other
operations including exposure to acids, which may produce Beryllium dust or fumes containing Beryllium
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11
AHP28XXS Series
Available Screening Levels and Process Variations for AHP28XXS Series.
MIL-STD-883
Method
Requirement
Temperature Range
No
Suffix
ES
Suffix
HB
Suffix
CH
Suffix
-20°C to +85°C
-55°C to +125°C
-55°C to +125°C
-55°C to +125°C
Element Evaluation
MIL-H-38534
9
9
9
1010
Cond B
Cond C
Cond C
2001, Y1 Axis
500g
3000g
3000g
Internal Visual
2017
Temperature Cycle
Constant Acceleration
Burn-in
‘
1015
48hrs @ 85°C
48hrs @ 125°C
160hrs @ 125°C
160hrs @ 125°C
MIL-PRF-38534
Specification
25°C
25°C
-55, +25, +125°C
-55, +25, +125°C
Seal, Fine & Gross
1014
Cond C
Cond A, C
Cond A, C
Cond A, C
External Visual
2009
‘
9
9
9
Final Electrical (Group A)
* per Commercial Standards
AHP28XXS Pin Designation
Pin No.
Designation
1
Positive Input
2
Input Return
3
Case
4
Enable 1
5
Sync Output
6
Sync Input
7
Positive Output
8
Output Return
9
Return Sense
10
Positive Sense
11
Share
12
Enable 2
Part Numbering
AHP 28 05 S X / CH
Model
Input Voltage
28 = 28V
270 = 270V
Output Voltage
05 = 5V, 08 = 8V
09 = 9V, 12 = 12V
15 = 15V, 28 = 28V
Screening Level
ES, HB, CH
Blank = min screening
Case Style
W, X, Y, Z
Outputs
S = Single
D = Dual
WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, Tel: (310) 322 3331
IR SANTA CLARA: 2270 Martin Av., Santa Clara, California 95050, Tel: (408) 727-0500
Visit us at www.irf.com for sales contact information.
Data and specifications subject to change without notice. 04/2009
12
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