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TECHNICAL DATASHEET
Rev. C
FA12S28-300
300W DC/DC Converter
10-36 Vdc Input
28Vdc Output at 10.7A
Full-Brick Package
FEATURES
 88% Efficient at Full Load
 Very Low Output Ripple
 90% Efficiency at 1/2 Load
 Fixed Switching Frequency
 Fast Transient Response
 Output Over Current Foldback
 Operation to No Load
 Output Short Circuit Protection
 Output Trim ±10%
 Over Temperature Protection
 Remote ON/OFF (Active High/Low)
 1500VDC Isolation
 Remote Sense Compensation
 100% Burn In
 Delivers a Continuous 150W at 25°C
 Synchronizable
with No Air / No Heatsink
 Single Output
DESCRIPTION
The FA series is a high-density full brick converter that incorporates the desired features required in today’s
demanding low voltage bus applications. Its unique dual interleaved phase-shifted topology minimizes both
input and output noise. When performance, reliability, and low cost are needed, the FA series delivers.
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1 of 13
WALL INDUSTRIES, INC.
Rev C
Technical Specifications
TECHNICAL DATASHEET
FA12S28-300
Model No. FA12S28-300
All specifications are based on 25°C, Nominal Input Voltage, and Maximum Output Current unless otherwise noted.
We reserve the right to change specifications based on technological advances.
SPECIFICATION
Related condition
Switching Frequency
INPUT (Vin)
Operating Voltage Range
UVLO Turn On at
UVLO Turn Off at
UVLO Hysteresis
Maximum Input Current (Graph 3)
No Load Input Current (Graph 3)
Input Current under “Remote Off”
Reflected Ripple Current
Input Surge Voltage
EFFICIENCY (Graph 1)
Low Line
No Load
With L-C filter as shown in Fig. 7.
100 mS
Io=10.714A
OUTPUT (Vo)
Voltage Set Point
±Sense shorted to ±Vout
Voltage Adjustment
Max Output limited to 300W
Load Regulation
Line Regulation
Temperature Drift
±Sense shorted to ±Vout
±Sense shorted to ±Vout
Remote Sense Compensation
Ripple (Photo4,5,6)
Spikes (Photo 4,5,6)
Current
Current Limit
Max Output limited to 300W
(max. drop in each + and – output trace)
0.1µF Ceramic & 10µF Tantalum
0.1µF Ceramic & 10µF Tantalum
Rated maximum output current
Power Limited-Dependent upon SENSE compensation
and TRIM adjustment
Over Voltage Limit
DYNAMIC RESPONSE
Load step /  V (Photo7)
Recovery Time (Photo 7)
Turn On Delay (Photo 1)
Turn On Overshoot (Photo 1,2)
Hold Up Time (Photo 3)
REMOTE ON/OFF
Remote ON – Positive logic
Remote OFF – Positive logic
Remote ON pin Floating - Positive logic
ION/OFF Sink current - Positive logic
Remote ON – Negative logic
Remote OFF – Negative logic
Remote ON/OFF pin Floating – Negative logic
ION/OFF Sink to pull low – Negative logic
ION/OFF Source to drive high – Active High or Low
Turn On Delay – (Photo 2)
Turn Off Delay – (Photo 3)
ISOLATION
Input-Output
Isolation Resistance
Isolation Capacitance
THERMAL
Ambient (Graph 2)
Over Temperature Protection
Storage Temperature
MTBF
MECHANICAL
Weight
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Min
Nom
Max
Unit
-
600
-
KHZ
10
9.5
9.0
-
12
9.7
9.25
0.5
35.7
0.10
1
20
86
36
10
9.5
50
-
Vdc
Vdc
Vdc
Vdc
A
A
mA
mA
Vdc
%
28.28
+1%
30.8
+10%
0.2
0.2
0.02
1
Vdc
%
%
%
% / °C
Vdc
240
240
10.714
mV p-p
mV p-p
A
27.72
-1%
25.2
-10%
-
28.00
0.05
0.05
0.01
-
-
0
50
50
-
-
15
-
A
31.6
35
38.6
Vdc
-
V
mS
mS
%
mS
5.0
2.0
5.0
1.0
2.0
5.0
4.7
1
1
10
Vdc
Vdc
Vdc
mA
Vdc
Vdc
-
Vdc
GΩ
µF
50% to 100% Io
Recovery to within 1% Nominal Vout
From Vin (min) to Vout (nom)
Full Load Resistive
1
0.4
50
0.0
0
Active High or Active Low (See page 13 for ordering details)
TTL high or Open-circuit
2.5
TTL Low
Over Operating Voltage Range
4.4
VON/OFF =0V, Vin=75V
Max Low to Enable
Min High to Disable
2.5
Over Operating Voltage Range
4.4
VON/OFF =0V, Vin=75V
Enabled
6
Disabled
1 minute
Max. Ambient limited by Derating Curves (Graph 2)
Self Resetting
Ambient
Calculated Using Bellcore TR-332 Method 1 case 3
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Vdc
1500
1
-
0.010
Graph 2
-40
25
110
-55
125
2,212,456
Hours
See Figure 1
318
-
mA
µA
mS
µS
°C
°C
°C
g
Page 2 of 13
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev C
FA12S28-300
Figure 1: Mechanical Dimensions
Unit: inches [mm]
HEATSINK SUPPLIED ATTACHED WITH
THERMAL INTERFACE MATERIAL.
HEATSINK HAS Ø.120 ±.005 Ø3.05±0.13 THRU HOLE 6X
.02 [0.4] 6X REF
COVER TO STANDOFF
.84±.04 [21.3±1.0]
HEATSINK
TO STANDOFFS ONLY
SEE NOTE 5
.000 [0.00]
.20 MIN [5.1 MIN]
SEE NOTE-1&3
PIN LENGTH FROM
STANDOFFS ONLY
.015 [0.38]
.02 [0.4] 6X REF
COVER TO STANDOFF
STANDARD
+0.8
.50+.03
-.00 12.7 -0.0
.20 MIN [5.1 MIN]
SEE NOTE-1&3
PIN LENGTH FROM
STANDOFFS ONLY
.30 [7.6]
.000 [0.00]
TO STANDOFFS ONLY
+0.5
.30+.02
-.03 7.6 -0.6
SEE NOTE-4
3.600 [91.44]
SERIAL NO:
1.800 [45.72]
.50 [12.7]
.35 [8.9]
.000 [0.00]
1
6
.400 [10.16]
2
7
.700 [17.78]
3
1.000 [25.40]
4
8
1.400 [35.56]
5
9
DATE CODE
4.200 [106.68]
NONMETALLIC INSULATOR 2X
.20±.03 [5.1±0.8]
+0.5
4.60 +.02
-.03 117.0 -0.8
2.100 [53.34]
MODEL NAME
DC/DC CONVERTER
R
XXXX
WALL INDUSTRIES
EXETER, NH 03833
DOT DENOTES
PIN-1
+0.5
2.40+.02
-.03 61.0 -0.8
LABEL
PIN DESIGNATION
1
+OUT
2
+SENSE
3
TRIM
4
-SENSE
5
-OUT
6
+IN
7
SD
8
SYNC
9
-IN
NOTES:
TO ORDER:
1. PIN TO PIN TOLERANCE ± .01 [±0.3],
PIN DIAMETER TOLERANCE: ±.005 [±0.13].
2. CASE MATERIAL: .040 [1.02] THICK, ALUMINUM ALLOY 3003-0,
PER: QQA 250/2.
3. UNLESS OTHERWISE SPECIFIED.
4. UNIT COMES WITH EITHER 3M x 0.5 THREADED
THRU INSERTS OR FOR Ø.125 THRU-HOLE ADD:
“TH” SUFFIX TO MODEL PART NUMBER.
EXAMPLE: FA12S28-300TH
5. FOR HEAT SINK ADD: “HS” SUFFIX TO MODEL
PART NUMBER. EXAMPLE: FA12S28-300HS.
6. OPTIONAL CHASSIS MOUNT VERSION
AVAILABLE (SEE CMFA SERIES).
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PIN Ø
Ø.081 [2.06]
Ø.040 [1.02]
Ø.040 [1.02]
Ø.040 [1.02]
Ø.081 [2.06]
Ø.081 [2.06]
Ø.040 [1.02]
Ø.040 [1.02]
Ø.081 [2.06]
Page 3 of 13
WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
DESIGN CONSIDERATIONS
Under Voltage Lock Out (UVLO)
The converter output is disabled until the input voltage exceeds the UVLO turn-on limit. The converter will remain ON until the input
voltage falls below the UVLO turn-off limit. There is approximately 0.5V hysteresis in the UVLO circuit.
Over Current Protection
The converter is internally protected from short circuit and over current conditions. During these fault conditions, the converter output
will “hiccup”- (short) or “fold back” - (over current). The converter output will recover once the short or over current fault is removed.
Over Temperature Protection
The converter is protected from over temperature conditions. Upon exceeding this temperature, the converter will shut down. The
converter will automatically recover once it has sufficiently cooled.
Input Filter
A 1,000µF low ESR capacitor across the input pins is recommended for most system level designs. No additional input capacitance is
needed for the power supply to operate with low impedance inputs. However, most “real world” system level integration will have some
amount of trace or wiring lengths – raising the inductive impedance. The added input capacitor will bring the impedance back towards
unity.
Output Filter
No additional output capacitor is needed for the power supply to operate within stated specifications. However, if it is a requirement to
reduce the ripple and noise on the output, additional capacitance may be added. Usually, ceramic MLCC’s capacitor works best for
reducing H.F. spike noise. Also, capacitance in the form of a tantalum or aluminum electrolytic capacitor may also be placed across the
output in order reduce base ripple, and improve the load transient peak-to-peak voltage deviation.
Remote Sense
To improve the voltage regulation at the load, route the connections from the -Sense and the +Sense pins to the –Vout and +Vout
connections AT the load. This will force the converter to regulate the voltage at the load and not at the pins of the converter. If it is not
desired to use the Remotes Sense feature, the –Sense and +Sense pins should be connected to the -Vout and +Vout pins respectively.
Fusing
It is required that the input to the converter be supplied with a maximum 50A, 250V rated fuse.
Safety
The FA series is CE pending and pending approval of the following: UL1950, CUL950, TUV60950 FILE 155800. The isolation
provided by the FA Series is a Basic insulation in accordance with EN60950. SELV output reliability is maintained only if the input to
the FA converter is an SELV source.
Remote ON/OFF
The FA Series has Remote ON/OFF (Enable/Disable) capability using TTL logic levels. This function is offered as either
Active=TTL High (no suffix) or Active=TTL Low (R suffix), see order details on page 13. For Remote ON/OFF limits, see page 2.
Figure 2. Remote (L/E)
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Synchronization
The FA series provides synchronization of switching frequencies between multiple FA series power supplies. The synchronization
function is accomplished without the need for any added external circuitry. By tying the SYNC pin between FA modules, they will all
automatically synchronize. If synchronization is not used, the pin should be tied to –Vin.
Output Voltage Trim
The following information is provided to allow quick calculation of the trim resistor value for a desired output voltage. The general
procedure for calculating a trim resistor is as follows:
1.
2.
3.
4.
Determine the desired output voltage deviation %.
To trim down, solve for resistor value using the “Rtlow” equation.
To trim up, solve for resistor value using the “Rthi” equation.
Solved resistor values are in KΩ.
Figure 3

 510
 10.2 
Rtlow  

 %
Figure 4

 5.1  Vo (100  %) 510
Rthi  

 10.2
%

 1.2225  %
Notes:
1.
2.
3.
4.
5.
Maximum trim range is ±10%. This includes remote sense drops if applicable.
Output current is limited to specified current when trimming down.
Output power is limited to specified power when trimming up.
Trim resistors should be placed close to the module.
If the trim function is not used, it is advised to leave the trim pin floating / not connected.
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Graph 1: FA12S28-300 Efficiency vs. Output Current
100%
95%
EFFICIENCY (%)
90%
85%
Low Line
80%
Nominal Line
75%
70%
High Line
65%
60%
55%
50%
0
2
4
6
8
10
12
OUTPUT CURRENT (AMPS)
Graph 2: FA12S28-300 Max Ambient vs. Output Power
OUTPUT POWER (WATTS)
300
250
0 LFM
100 LFM
200
200 LFM
150
300 LFM
400 LFM
100
Airflow across unit in linear
feet per minute (LFM)
50
0
-40 -30 -20 -10 0
10 20 30 40 50 60 70 80 90 100 110
AMBIENT TEMPERATURE (DEG. C.)
Note: When trimming the output high, Io vs. Ambient is derated by power. i.e.: from Graph 2, find the maximum current at the desired
ambient and airflow, and multiply this current by the nominal voltage (28V) to get the maximum power. Divide this power by the desired
trimmed high voltage to get the maximum current at that ambient. When trimming low, the maximum current stays the same as shown in
graph 2.
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WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev C
FA12S28-300
Graph 3: Input Current vs. Input Voltage
40.00
INPUT CURRENT (AMPS)
35.00
30.00
Io=2.68A
25.00
Io=5.36A
20.00
Io=8.04A
15.00
Io=10.714A
10.00
5.00
0.00
0
5
10
15
20
25
30
35
40
INPUT VOLTAGE
FA12S28-300
POWER DISSIPATION (WATTS)
Graph 4: Power Dissipation vs. Input Voltage
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Io=0A
Io=2.68A
Io=5.36A
Io=8.04A
Io=10.714A
0
5
10
15
20
25
30
35
40
INPUT VOLTAGE
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Photo 1: Full load (resistive) startup.
Ch.1 = Vin (5V/div), CH.2 = Vout (10V/div).
Photo 2: Full load (resistive) startup, via logic enable.
Ch. 1 = L/E (2V /div), Ch.2 = Vout (5V/div).
Photo 3: Full load turn-off, via logic enable.
Ch.1 = L/E (2V/div), Ch.2 = Vout (5V/div).
Photo 4: Output ripple, 10Vin, full load.
10mV / div.
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Photo 5. Output ripple, 24Vin, full load.
20mV / div.
Photo 6: . Output ripple, 36Vin, full load.
50mV / div.
Photo 7: Transient Response 50% to 100%
Vin=24V, Iout = 5.357A to 10.714A @ 1V/ Div
Cout=0.1uF Ceramic + 10uF Tantalum
Photo 8: Overload output current, 0.2 Ohm impedance.
24Vin, 10A / div.
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
TEST SETUP:
The FA12S28-300 specifications are tested with the following configurations:
Regulation and Efficiency Setup
To ensure that accurate measurements are taken, the voltage measurements are taken directly at the terminals of the module. This
minimizes errors due to contact and trace lengths between the load and the output of the supply. The following diagram is of the test
setup.
Figure 5: Regulation and Efficiency Probe Setup
Output Ripple Voltage Setup
The module is tested with a 0.1µF ceramic capacitor in parallel with a 10µF tantalum capacitor across the output terminals. Unless
otherwise specified, bandwidth is limited to 20MHZ.
Figure 6: Ripple Voltage Probe Setup
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WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Input Reflected Ripple Current and Input Ripple Voltage Setup
The module is tested for input reflected ripple current (Irrc). The input ripple voltage is also measured at the pins with and without an
additional 33µF electrolytic capacitor. To reduce either the input ripple current or voltage additional capacitors and/or an inductor may be
added to the input of the converter.
Figure 7: Ripple Current Setup
Converter Thermal Consideration
The converter is designed to operate without convective cooling if the de-rating curves are followed. The converter can operate at higher
temperatures and higher output currents if airflow and/or a heatsink are applied. Airflow should be aligned lengthwise to the converter’s
heatsink fins for optimum heat transfer. See Graph 2 for de-rating curves or contact factory for additional thermal information.
Figure 8: Airflow Orientation
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Page 11 of 13
WALL INDUSTRIES, INC.
Rev C
TECHNICAL DATASHEET
FA12S28-300
Paralleling Converters
The FA series converters may be paralleled both for redundancy and for higher output current. However, in order to do this, a highcurrent, low Vf, Schottky diode must be placed at the +Vo pin of each supply as shown in Figure 9.
Figure 9: Paralleling Converters
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Page 12 of 13
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev C
FA12S28-300
Ordering Information:
Part Number Example:
FA 12 S 28 – 300 R TH – HS
Series
Designation
Nominal
Input
Voltage
Single
Output
Nominal
Output
Voltage
Options
No Suffix
HS
Options
No Suffix
Maximum
Output
Power
TH
Options
No Suffix
R
No Heat Sink
With Heat Sink
Threaded Thru Inserts
(3M x 0.5)
Through Hole
Active High Enable
Active Low Enable
Company Information:
Wall Industries, Inc. has created custom and modified units for over 50 years. Our in-house research and development
engineers will provide a solution that exceeds your performance requirements on time and on budget. Our ISO9001-2008
certification is just one example of our commitment to producing a high quality, well-documented product for our customers.
Our past projects demonstrate our commitment to you, our customer. Wall Industries, Inc. has a reputation for working
closely with its customers to ensure each solution meets or exceeds form, fit and function requirements. We will continue to
provide ongoing support for your project above and beyond the design and production phases. Give us a call today to discuss
your future projects.
Contact Wall Industries for further information:
Phone:
Toll Free:
Fax:
E-mail:
Web:
Address:
(888) 597-WALL
 (603)778-2300
 (888)587-9255
 (603)778-9797
sales@wallindustries.com
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5 Watson Brook Rd.
Exeter, NH 03833
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Page 13 of 13