AFL2808DZ/ES [ETC]
DC to DC Converter ; 直流到直流转换器\n
| 型号： | AFL2808DZ/ES |
| 厂家： | 
ETC |
| 描述： | DC to DC Converter
|
| 文件： | 总12页 (文件大小：123K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
l
LAMBDA ADVANCED ANALOG INC.
AFL12000S Series
Single Output, Hybrid - High Reliability
DC/DC Converters
DESCRIPTION
FEATURES
Lambda
requirements.
Advanced
Analog
with
specific
The AFL Series of DC/DC converters feature high
power density with no derating over the full military
temperature range. This series is offered as part of
a complete family of converters providing single and
dual output voltages and operating from nominal
+28, +50, +120 or +270 volt inputs and output power
ranging from 80 to 120 watts. For applications
requiring higher output power, individual converters
can be operated in parallel. The internal current
sharing circuits assure accurate current distribution
among the paralleled converters. This series
incorporates Lambda Advanced Analog'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. Undervoltage lockout, primary and
secondary referenced inhibit, soft-start and load
fault protection are provided on all models.
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80 To 160 Volt Input Range
5, 8, 9, 12, 15, 24 and 28 Volt Outputs
Available
n
n
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High Power Density - up to 84 W / in3
Up To 120 Watt Output Power
Parallel Operation with Stress and Current
Sharing
n
n
n
n
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Low Profile (0.380") Seam Welded Package
Ceramic Feedthru Copper Core Pins
High Efficiency - to 87%
Full Military Temperature Range
Continuous Short Circuit and Overload
Protection
n
n
Remote Sensing Terminals
Primary and Secondary Referenced Inhibit
Functions
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 Lambda Advanced
Analog's rugged ceramic lead-to-package seal
assuring long term hermeticity in the most harsh
environments.
n
n
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Line Rejection > 50 dB - DC to 50 KHz
External Synchronization Port
Fault Tolerant Design
Dual Output Versions Available
Standard Military Drawings Available
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-PRF-38534 for class H.
The HB grade is fully processed and screened to the
class H requirement, may not necessarily meet all of
the other MIL-PRF-38534 requirements, e.g.,
element evaluation and Periodic Inspections (PI) not
required. Both grades are tested to meet the
complete group "A" test specification over the full
military temperature range without output power
deration. Two grades with more limited screening
are also available for use in less demanding
applications. Variations in electrical, mechanical
and screening can be accommodated. Contact
1
SPECIFICATIONS
AFL120XXS
ABSOLUTE MAXIMUM RATINGS
Input Voltage
-0.5V to 180V
300°C for 10 seconds
Soldering Temperature
Case Temperature
Operating
Storage
-55°C to +125°C
-65°C to +135°C
Static Characteristics -55°C £ TCASE £ +125°C, 80V £ VIN £ 160V unless otherwise specified.
Group A
Parameter
INPUT VOLTAGE
Subgroups
Test Conditions
Min
Nom
Max
Unit
Note 6
80
120
160
V
OUTPUT VOLTAGE
VIN = 120 Volts, 100% Load
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
1
1
1
1
1
1
1
4.95
7.92
8.91
11.88
14.85
23.76
27.72
5.00
8.00
9.00
12.00
15.00
24.00
28.00
5.05
8.08
9.09
12.12
15.15
24.24
28.28
V
V
V
V
V
V
V
4.90
7.84
8.82
11.76
14.70
23.52
27.44
5.10
8.16
9.18
12.24
15.30
24.48
28.56
V
V
V
V
V
V
V
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
2, 3
OUTPUT CURRENT
VIN = 80, 120, 160 Volts - Note 6
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
16.0
10.0
10.0
9.0
8.0
4.0
A
A
A
A
A
A
A
4.0
OUTPUT POWER
Note 6
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
80
80
90
108
120
96
W
W
W
W
W
W
W
112
MAXIMUM CAPACITIVE LOAD
Note 1
10,000
-0.015
mfd
OUTPUT VOLTAGE
VIN = 120 Volts, 100% Load - Note 1, 6
+0.015 %/°C
TEMPERATURE COEFFICIENT
OUTPUT VOLTAGE REGULATION
AFL12028S
All Others
Line
Line
1, 2, 3
1, 2, 3
No Load, 50% Load, 100% Load
VIN = 80, 120, 160 Volts
-70.0
-20.0
+70.0
+20.0
mV
mV
Load
1, 2, 3
-1.0
+1.0
%
2
Static Characteristics (Continued)
Group A
Parameter
Subgroups
Test Conditions
Min Nom Max
Unit
OUTPUT RIPPLE VOLTAGE
VIN = 80, 120, 160 Volts, 100% Load,
BW = 10MHz
AFL12005S
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
30
40
40
45
50
mVpp
mVpp
mVpp
mVpp
mVpp
mVpp
mVpp
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
80
100
VIN = 120 Volts
IOUT = 0
INPUT CURRENT
No Load
1
2, 3
1, 2, 3
1, 2, 3
30
40
3
mA
mA
mA
mA
Pin 4 Shorted to Pin 2
Pin 12 Shorted to Pin 8
Inhibit 1
Inhibit 2
5
INPUT RIPPLE CURRENT
AFL12005S
VIN = 120 Volts, 100% Load, BW = 10MHz
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
60
60
70
70
80
80
80
mApp
mApp
mApp
mApp
mApp
mApp
mApp
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
CURRENT LIMIT POINT
As a percentage of full rated load
VOUT = 90% VNOM , V = 120 Volts
IN
Note 5
1
2
3
115
105
125
125
115
140
%
%
%
LOAD FAULT POWER DISSIPATION
VIN = 120 Volts
Overload or Short Circuit
1, 2, 3
32
W
EFFICIENCY
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
VIN = 120 Volts, 100% Load
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
78
79
80
82
83
82
82
82
83
84
85
87
85
85
%
%
%
%
%
%
%
ENABLE INPUTS (Inhibit Function)
Converter Off
1, 2, 3
1, 2, 3
Logical Low on Pin 4 or Pin 12
Note 1
Logical High on Pin 4 and Pin 12 - Note 9
Note 1
-0.5
2.0
0.8
100
50
V
mA
V
Sink Current
Converter On
Sink Current
100
mA
SWITCHING FREQUENCY
1, 2, 3
500
550
600
KHz
SYNCHRONIZATION INPUT
Frequency Range
1, 2, 3
1, 2, 3
1, 2, 3
500
2.0
-0.5
700
10
0.8
100
80
KHz
V
V
nSec
%
Pulse Amplitude, Hi
Pulse Amplitude, Lo
Pulse Rise Time
Note 1
Note 1
Pulse Duty Cycle
20
ISOLATION
1
Input to Output or Any Pin to Case
(except Pin 3). Test @ 500VDC
100
MW
DEVICE WEIGHT
MTBF
Slight Variations with Case Style
85
gms
MIL-HDBK-217F, AIF @ TC = 40°C
300
KHrs
3
Dynamic Characteristics -55°C £ TCASE £ +125°C, VIN = 120 Volts unless otherwise specified.
Group A
Parameter
Subgroups
Test Conditions
Min
Nom
Max
Unit
LOAD TRANSIENT RESPONSE
Note 2, 8
AFL12005S
AFL12008S
AFL12009S
AFL12012S
AFL12015S
AFL12024S
AFL12028S
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-450
-450
450
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
450
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-500
-500
500
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
500
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-600
-600
600
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
600
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-750
-750
750
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
750
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-900
-900
900
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
900
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-900
-900
900
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
900
400
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
Load Step 50% Û 100%
Load Step 10% Û 50%
-1200
-1200
1200
200
mV
mSec
Amplitude
Recovery
4, 5, 6
4, 5, 6
1200
400
mV
mSec
LINE TRANSIENT RESPONSE
Note 1, 2, 3
VIN Step = 80 Û 160 Volts
Amplitude
Recovery
-500
500
500
mV
mSec
TURN-ON CHARACTERISTICS
Note 4
Overshoot
Delay
4, 5, 6
4, 5, 6
Enable 1, 2 on. (Pins 4, 12 high or open)
250
120
mV
mSec
50
50
75
60
LOAD FAULT RECOVERY
LINE REJECTION
Same as Turn On Characteristics.
MIL-STD-461D, CS101, 30Hz to 50KHz
Note 1
dB
Notes to Specifications:
1.
2.
3.
4.
5.
6.
7.
8.
9.
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 VOUT has returned to within ±1% of VOUT at 50% load.
Line transient transition time ³ 100 mSec.
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 ³ 10 mSec.
Enable inputs internally pulled high. Nominal open circuit voltage » 4.0VDC.
4
AFL12000S Case Outlines
Case X
Case W
Pin Variation of Case Y
3.000
2.760
ø 0.128
0.050
0.050
0.250
0.250
1.000
1.000
Ref
1.260 1.500
0.200 Typ
Non-cum
Pin
ø 0.040
Pin
ø 0.040
0.220
2.500
0.220
0.525
2.800
2.975 max
0.238 max
0.42
0.380
Max
0.380
Max
Case Y
Case Z
Pin Variation of Case Y
0.300
ø 0.140
1.150
0.050
0.25 typ
0.050
0.250
0.250
1.000
Ref
1.000
Ref
1.500 1.750 2.00
0.200 Typ
Non-cum
Pin
ø 0.040
Pin
ø 0.040
0.220
0.220
1.750
2.500
0.375
0.36
2.800
2.975 max
0.525
0.238 max
0.380
Max
0.380
Max
5
AFL12000S Pin Designation
Pin No.
Designation
1
2
Positive Input
Input Return
Case
3
4
Enable 1
5
Sync Output
Sync Input
Positive Output
Output Return
Return Sense
Positive Sense
Share
6
7
8
9
10
11
12
Enable 2
Available Screening Levels and Process Variations for AFL 12000S Series.
MIL-STD-883
Method
No
Suffix
ES
Suffix
HB
Suffix
CH
Suffix
Requirement
Temperature Range
Element Evaluation
Internal Visual
-20°C to +85°C
-55°C to +125°C
-55°C to +125°C
-55°C to +125°C
MIL-H-38534
ü
2017
1010
¬
ü
Cond B
500g
ü
Cond C
Temperature Cycle
Constant Acceleration
Burn-in
Cond C
2001,
Cond A
Cond A
1015
96hrs @ 125°C
25°C
160hrs @ 125°C
-55, +25, +125°C
Cond A, C
ü
160hrs @ 125°C
-55, +25, +125°C
Cond A, C
ü
Final Electrical (Group A)
Seal, Fine & Gross
External Visual
MIL-PRF-38534
1014
25°C
Cond A
¬
Cond A, C
ü
2009
¬ per Commercial Standards
Part Numbering
AFL120 05 S X / CH
Model
Screening
–
, ES
HB, CH
Input Voltage
Case Style
W, X, Y, Z
28= 28 V, 50= 50 V
120=120 V, 270= 270 V
Output Voltage
03.3= 3.3 V, 05= 5 V
08= 8 V, 09= 9 V
Outputs
S = Single
D = Dual
12= 12 V, 15= 15 V
24= 24 V, 28= 28 V
6
AFL12000S Circuit Description
Figure I. AFL Single Output Block Diagram
Input
Filter
1
4
5
DC Input
Enable 1
Output
Filter
+Output
+Sense
7
Primary
Bias Supply
10
Current
Sense
Sync Output
Share
Amplifier
Control
11 Share
Error
Amp
& Ref
Sync Input
Case
6
3
2
Enable 2
FB
12
Sense
Amplifier
9
8
-Sense
Output Return
Input Return
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.
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 pin 4
is enabled (at a logical 1 or open) the primary bias
supply will begin generating
a
regulated
Inhibiting Converter Output
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.
Figure II. Enable Input Equivalent Circuit
+5.6V
100K
1N4148
Pin 4 or
Pin 12
Disable
290K
Remote Sensing
2N3904
Connection of the + and - sense leads at a remotely
located load permits compensation for excessive
resistance between the converter output and the
150K
Pin 2 or
Pin 8
7
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).
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.
Synchronization of Multiple Converters
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 AFL 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
When operating multiple converters, system
requirements often dictate operation of the
converters at
a
common frequency.
To
accommodate this requirement, the AFL series
converters provide both a synchronization input and
a synchronization output.
The sync input port permits synchronization of an
AFL converter 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
additional converters.
illustrated in Figure III.
A typical connection is
Figure III. Preferred Connection for Parallel Operation
1
12
Power
Input
Enable 2
Share
Vin
Rtn
Case
+ Sense
- Sense
Return
AFL
AFL
Enable 1
Sync Out
Sync In
+ Vout
7
6
1
Optional
Synchronization
Connection
Share Bus
12
Enable 2
Share
Vin
Rtn
Case
+ Sense
- Sense
Return
Enable 1
Sync Out
Sync In
to Load
+ Vout
7
6
1
12
Enable 2
Share
Vin
Rtn
Case
+ Sense
- Sense
Return
AFL
Enable 1
Sync Out
Sync In
+ Vout
7
6
(Other Converters)
Parallel Operation — Current and Stress Sharing
permits equal sharing among the members of a set
where total load current exceeds the capacity of an
individual AFL. An important feature of the AFL
series operating in the parallel mode is that in
addition to sharing the current, the stress induced by
Figure III. illustrates the preferred connection
scheme for operation of a set of AFL converters with
outputs operating in parallel. Use of this connection
8
under the trade name of Sil-Padâ 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 are
frequently messy to use.
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.
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 sense leads from each converter 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
A conservative aid to estimating the total heat sink
surface area (AHEAT SINK) required to set the maximum
case temperature rise (DT) above ambient
temperature is given by the following expression:
their share pins connected together.
This
arrangement is diagrammatically illustrated in
Figure III. showing the outputs and sense pins
connected at a star point which is located close as
possible to the load.
ì
í
î
ü- 1.43
ý
- 3.0
DT
A
HEAT SINK
»
0.85 þ
80P
where
DT = Case temperature rise above ambient
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 output
current to +2.20v at full load.
ì
OUTí
î
ü
1
ý
- 1
P = Device dissipation in Watts = P
Eff
þ
As an example, it is desired to maintain the case
temperature of an AFL12015S at £ +85°C while
operating in an open area whose ambient
temperature is held at a constant +25°C; then
Thermal Considerations
DT = 85 - 25 = 60°C.
Because of the incorporation of many innovative
technological concepts, the AFL 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.
If the worst case full load efficiency for this device is
83%; then the power dissipation at full load is given
by
ì
ü
1
í
ý
- 1 = 120· (0.205) = 24.6W
P = 120·
î .83
þ
and the required heat sink area is
ì
í
î
ü- 1.43
- 3.0 = 71 in2
ý
60
A
HEAT SINK
=
0.85 þ
80· 24.6
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 in2 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.
Because 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
1
Sil-Pad is a registered Trade Mark of Bergquist, Minneapolis, MN
9
Input Filter
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.
The AFL12000S series converters incorporate a LC
input filter whose elements dominate the input load
impedance characteristic at turn-on. The input
circuit is as shown in Figure IV.
Figure V. Connection for VOUT Adjustment
Figure IV. Input Filter Circuit
Enable 2
16.8uH
Share
RADJ
Pin 1
+ Sense
AFL120xxS
- Sense
0.78uF
Return
To Load
+ V
out
Pin 2
Note: Radj must be set ³ 500W
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
Undervoltage Lockout
A minimum voltage is required at the input of the
converter to initiate operation. This voltage is set to
75 ± 3 volts. To preclude the possibility of noise or
other variations at the input falsely initiating and
to failure.
Under no circumstance should the
external setting resistor be made less than 500W.
By remaining within this specified range of values,
completely safe operation fully within normal
component derating limits is assured.
halting converter operation,
a
hysteresis of
approximately 4 volts is incorporated in this circuit.
Thus if the input voltage drops to 71 ± 3 volts, the
converter will shut down and remain inoperative
until the input voltage returns to »75 volts.
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 AFL12000S 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 » 25mV above nominal device voltage.
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 between
the +sense and -sense pins while connecting the -
sense pin to the output return pin as shown in Figure
The consequence is that if the +sense connection is
unintentionally broken, an AFL120xxS has a fail-
safe output voltage of Vout + 25mV, where the
25mV 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 + 440mV. This 440
mV is also essentially constant independent of the
nominal output voltage.
V. below.
The range of adjustment and
corresponding range of resistance values can be
determined by use of the following equation.
General Application Information
The AFL12000 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
ì
í
î
ü
ý
þ
VNOM
Radj = 100·
VOUT - VNOM -.025
Where VNOM = device nominal output voltage, and
VOUT = desired output voltage
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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 approximately
100µfd be connected directly across the input
terminals to assure an adequately low impedance at
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.
the input terminals. Table
I
relates nominal
resistance values and selected wire sizes.
Table I. Nominal Resistance Of Cu Wire
Wire Size, AWG
Resistance per ft
24 Ga
22 Ga
20 Ga
18 Ga
16 Ga
14 Ga
12 Ga
25.7 mW
16.2 mW
10.1 mW
6.4 mW
4.0 mW
2.5 mW
1.6 mW
Figure VI. Problems of Parasitic Resistance in Input Leads
(See text)
Rp
Rp
Iin
Vin
100
µfd
esource
Rtn
eRtn
IRtn
Case
Enable 1
Sync Out
Sync In
System Ground
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The information in this data sheet has been carefully checked and is believed to be accurate; however no
responsibility is assumed for possible errors. These specifications are subject to change without notice.
Ó
Lambda Advanced Analog
981027
2270 Martin Avenue
Santa Clara CA 95050-2781
(408) 988-4930 FAX (408) 988-2702
MIL-PRF-38534 Qualified
ISO9001 Registered
l
LAMBDA ADVANCED ANALOG INC.
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