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TECHNICAL DATASHEET
Rev. D
CMFA12S24-300
300W DC-DC Chassis Mount Converter
10-36 Vdc Input
24Vdc Output at 12.5A
Full-Brick Package
Features:
 88% Efficient at Full Load
 90% Efficiency at 1/2 Load
 Fast Transient Response
 Operation to No Load
 Output Trim ±10%
 Remote ON/OFF (Active High/Low)
 Remote Sense Compensation
 Delivers a Continuous 150W at 25°C
with No Air / No Heatsink








Very Low Output Ripple
Fixed Switching Frequency
Output Over Current Foldback
Output Short Circuit Protection
Over Temperature Protection
1500 V Isolation
100% Burn In
Synchronizable
Description:
The CMFA Series is a high-density full brick converter on a chassis mount 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 CMFA Series delivers.
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Page 1 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
Model No. CMFA12S24-300
Technical Specifications
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
Switching Frequency
INPUT (Vin)
Operating Voltage Range
UVLO Turn On at
UVLO Turn Off at
UVLO Hysterisis
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)
OUTPUT (Vo)
Related condition
Low Line
No Load
With L-C filter as shown in Fig. 7.
100 mS
Io=12.5A
Voltage Set Point
±Sense shorted to ±Vout
Voltage Adjustment (Table1)
Max Output limited to 300W
Load Regulation
Line Regulation
Temperature Drift
±Sense shorted to ±Vout
±Sense shorted to ±Vout
Remote Sense Compensation
Ripple
Spikes
Current
Current Limit
Over Voltage Limit
DYNAMIC RESPONSE
Load step /  V
Recovery Time
Turn On Delay
Turn On Overshoot
Hold Up Time
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
Turn Off Delay
ISOLATION
Input-Output
Isolation Resistance
Isolation Capacitance
THERMAL
Ambient (Graph 2)
Over Temperature Protection
Storage Temperature
MTBF
MECHANICAL
Weight
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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
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
%
24.250
+1%
26.4
+10%
0.2
0.2
0.02
1
Vdc
%
%
%
% / °C
Vdc
23.74
-1%
21.6
-10%
-
24.00
0.05
0.05
0.01
-
-
0
50
50
-
240
240
12.5
mV p-p
mV p-p
A
-
17.5
-
A
27
30
33
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 12 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
1500
1
-40
-55
-
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Vdc
0.010
mA
µA
mS
µS
Graph 2
25
110
125
2,212,456
See Figure 1
318
-
°C
°C
°C
Hours
g
Page 2 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
CMFA12S24-300
Rev D
Figure 1: Mechanical Dimensions
Unit: inches [mm]
8.00 [203.2]
7.000 [177.80]
3.500 [88.90]
.50 [12.7]
+INPUT
+OUTPUT
+S
SD
3.40 [86.4]
2.875 [73.03]
TRIM
SYNC
-S
-INPUT
-OUTPUT
.000 [0.00]
.26 [6.7]
DATE CODE
LABEL
SERIAL NO:
UNIT THRU HOLE Ø.125 [3.2] 6X REF
PCB THRU HOLE Ø.140 [3.6] 6X REF
Ø.143 [3.6] MOUNTING HOLES 6X
GROUNDED 6-PLACES
TERMINAL SCREW .136 (NO:6)-32UNC 9X
.91 [23.0]
.24 [6.0] REF
Ø.28 [7.1] 6X
.000 [0.00]
.13 [3.2] 6X REF
.000 [0.00]
TO ORDER
1. Unit comes with either 3M x 0.5 threaded thru inserts for the
chassis mount board or Ø.125 thru-hole for the chassis
mount board add the suffix "TH" to the model part number.
Ex: CMFA12S24-300TH.
2. For Heat Sink Add “HS” suffix to model part number.
Ex: CMFA12S24-300HS
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Page 3 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
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.
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 50 A, 250 V rated fuse.
Safety
The CMFA series is CE pending and pending approval of the following: UL1950, CUL950, TUV60950 FILE 155800. The isolation
provided by the CMFA Series is a Basic insulation in accordance with EN60950. SELV output reliability is maintained only if the input
to the CMFA converter is an SELV source.
Remote ON/OFF
The CMFA 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 12. For Remote ON/OFF limits, see page 2.
Figure 2. Remote (L/E)
Synchronization
The CMFA 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 CMFA modules, they will all
automatically synchronize. If synchronization is not used, the pin should be tied to –Vin.
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Page 4 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
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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Page 5 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
CMFA12S24-300
Rev D
Graph 1: CMFA12S24-300 Efficiency vs. Output Current
100%
95%
EFFICIENCY (%)
90%
Low Line
85%
80%
Nominal Line
75%
High Line
70%
65%
60%
55%
50%
0
2
4
6
8
10
12
14
OUTPUT CURRENT (AMPS)
Graph 2: CMFA12S24-300 Max Ambient vs. Output Power
OUTPUT POWER (WATTS)
300
250
0 LFM
200
100 LFM
200 LFM
150
300 LFM
400 LFM
100
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 (24V) 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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Page 6 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
CMFA12S24-300
Rev D
Graph 3: Input Current vs. Input Voltage
40.00
INPUT CURRENT (AMPS)
35.00
30.00
Io=3.12A
25.00
Io=6.25A
20.00
Io=9.37A
15.00
Io=12.5A
10.00
5.00
0.00
0
5
10
15
20
25
30
35
40
INPUT VOLTAGE
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=3.12A
Io=6.25A
Io=9.37A
Io=12.5A
0
5
10
15
20
25
30
35
40
INPUT VOLTAGE
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Page 7 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
CMFA12S24-300
Rev D
Graph 5: Input Current Characteristics at Light Load
3.5
3
Input Current
2.5
No Load
0.125A
2
0.250A
0.500A
1.5
0.750A
1.000A
1
0.5
0
10
15
20
25
30
35
40
Input voltage
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Page 8 of 12
WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
TEST SETUP:
The CMFA12S24-300 specifications are tested with the following configurations:
Regulation and Efficiency Setup
To ensure that accurate measurement 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.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
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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WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
Rev D
CMFA12S24-300
Paralleling Converters
The CMFA 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. To improve sharing, tie the two
TRIM pins together. The converters may be trimmed by adding a resistor value from each TRIM pin to ±RS pin, or alternatively, a single
resistor of half the value from the common TRIM pins to the common ±RS pins.
Figure 9: Paralleling Converters
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WALL INDUSTRIES, INC.
TECHNICAL DATASHEET
CMFA12S24-300
Rev D
Ordering Information:
Part Number Example:
CMFA 12 S 24 – 300 R TH
Series
Designation
Nominal
Input Voltage
Single
Output
Nominal
Output Voltage
Options
Maximum
Output Power
No Suffix
TH
HS
Threaded Thru Inserts
(3M x 0.5)
Thru-Hole Inserts
Heat sink
Options
No suffix Active High Enable (standard)
R
Active Low Enable (option)
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:
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 (603)778-2300
 (888)587-9255
 (603)778-9797
[email protected]
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5 Watson Brook Rd.
Exeter, NH 03833
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Page 12 of 12