Page 1
LM2825
Integrated Power Supply 1A DC-DC Converter
LM2825 Integrated Power Supply 1A DC-DC Converter
May 1997
General Description
The LM2825 is a complete 1A DC-DC Buck converter packaged in a 24-lead molded Dual-In-Line integrated circuit
package.
Contained within the package are all the active and passive
components for ahighefficiency step-down (buck) switching
regulator. Available in fixed output voltages of 3.3V, 5V and
12V, as well as two adjustable versions, these devices can
provide up to 1A of load current with fully guaranteed electrical specifications.
Self-contained, this converter is also fully protected from output fault conditions, such as excessive load current, short
circuits, or excessive temperatures.
Highlights
n No external components required (fixed output voltage
versions)
n Integrated circuit reliability
n MTBF over 20 million hours
n Radiated EMI meets Class B stipulated by CISPR 22
n High power density, 35 W/in
n 24-pin DIP package profile (1.25 x 0.54 x 0.26 inches)
3
DS012661-27
Features
n Minimum design time required
n 3.3V, 5V and 12V fixed output versions
n Two adjustable versions allow 1.23V to 15V outputs
n Wide input voltage range, up to 40V
n Low-power standby mode, I
n High efficiency, typically 80
±
n
4%output voltage tolerance
n Excellent line and load regulation
n TTL shutdown capability/programmable Soft-start
n Thermal shutdown and current limit protection
n −40˚C to +85˚C ambient temperature range
typically 65 µA
Q
%
Applications
n Simple high-efficiency step-down (buck) regulator
n On-card switching regulators
n Efficient pre-regulator for linear regulators
n Distributed power systems
n DC/DC module replacement
Connection Diagram
Standard Application
(Fixed output voltage versions)
“NC (Do not use)” pins: See
DS012661-1
Radiated EMI
Radiated emission of electromagnetic fields is measured at
10m distance. The emission levels are within the Class B
limits stipulated by CISPR 22.
30. . . .230 MHz 30 dB µV/m
230. . . .1000 MHz 37 dB µV/m
1. . . .10 GHz 46 dB µV/m
© 1997 National Semiconductor Corporation DS012661 www.national.com
Ordering Information
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N-12,
LM2825N-ADJ or LM2825HN-ADJ
See NS Package Number NA24F
Figure 11
Top View
.
DS012661-2
Page 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
ESD Susceptibility
Human Body Model (Note 3) 2 kV
Lead Temperature (Soldering 10 sec.) 260˚C
Distributors for availability and specifications.
Maximum Input Supply (V
) +45V
IN
SD/SS Pin Input Voltage (Note 2) 6V
Output Pin Voltage
(3.3V, 5.0V and ADJ) −1V ≤ V ≤ 9V
(12V and H-ADJ) −1V ≤ V ≤ 16V
ADJ Pin Voltage (ADJ, H-ADJ only) −0.3V ≤ V ≤ 25V
Power Dissipation Internally Limited
Operating Ratings
Ambient Temperature Range −40˚C ≤ TA≤ +85˚C
Junction Temperature Range −40˚C ≤ T
Input Supply Voltage (3.3V version) 4.75V to 40V
Input Supply Voltage (5V version) 7V to 40V
Input Supply Voltage (12V version) 15V to 40V
Input Supply Voltage (-ADJ, H-ADJ) 4.5V to 40V
≤ +125˚C
J
Storage Temperature Range −40˚C to +125˚C
LM2825-3.3 Electrical Characteristics (Note 4)
LOAD
IN
IN
IN
=
25˚C, and those with boldface type apply over full Operating Tempera-
A
Typical Limit
(Note 6) (Note 7)
≤ 1A 3.3 V
LOAD
3.168/3.135 V(min)
3.432/3.465 V(max)
≤ 40V 1.5 mV
IN
=
100 mA
≤ 1A 8 mV
LOAD
=
12V
=
=
12V, I
12V, I
=
1A 40 mV p-p
LOAD
=
0.5A 75
LOAD
(Limits)
%
Specifications with standard type face are for T
Figure 2
ture Range. Test Circuit
.
Symbol Parameter Conditions LM2825-3.3 Units
V
Output Voltage 4.75V ≤ VIN≤ 40V, 0.1A ≤ I
OUT
Line Regulation 4.75V ≤ V
I
Load Regulation 0.1A ≤ I
V
Output Ripple Voltage V
η Efficiency V
LM2825-5.0 Electrical Characteristics (Note 4)
Specifications with standard type face are for T
Figure 2
ture Range. Test Circuit
.
Symbol Parameter Conditions LM2825-5.0 Units
V
Output Voltage 7V ≤ VIN≤ 40V, 0.1A ≤ I
OUT
Line Regulation 7V ≤ V
I
Load Regulation 0.1A ≤ I
V
Output Ripple Voltage V
η Efficiency V
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=
25˚C, and those with boldface type apply over full Operating Tempera-
A
Typical Limit
(Note 6) (Note 7)
≤ 1A 5.0 V
LOAD
4.800/4.750 V(min)
5.200/5.250 V(max)
≤ 40V 2.7 mV
IN
=
100 mA
LOAD
IN
IN
IN
≤ 1A 8 mV
LOAD
=
12V
=
=
12V, I
12V, I
=
1A 40 mV p-p
LOAD
=
0.5A 80
LOAD
(Limits)
%
Page 3
LM2825-12 Electrical Characteristics (Note 4)
Specifications with standard type face are for T
Figure 2
ture Range. Test Circuit
.
Symbol Parameter Conditions LM2825-12 Units
V
OUT
Output Voltage 15V ≤ VIN≤ 40V, 0.1A ≤ I
Line Regulation 15V ≤ V
I
LOAD
Load Regulation 0.1A ≤ I
V
Output Ripple Voltage V
η Efficiency V
IN
IN
IN
=
25˚C, and those with boldface type apply over full Operating Tempera-
A
Typical Limit
(Note 6) (Note 7)
≤ 0.75A 12.0 V
LOAD
11.52/11.40 V(min)
12.48/12.60 V(max)
≤ 40V 8.5 mV
IN
=
100 mA
≤ 0.75A 12 mV
LOAD
=
24V
=
=
24V, I
24V, I
=
1A 100 mV p-p
LOAD
=
0.5A 87
LOAD
(Limits)
%
LM2825-ADJ Electrical Characteristics (Note 5)
Specifications with standard type face are for T
Figure 3
ture Range. Test Circuit
.
Symbol Parameter Conditions LM2825-ADJ Units
V
ADJ
Adjust Pin Voltage 4.5V ≤ VIN≤ 40V, 0.1A ≤ I
1.23V ≤ V
η Efficiency V
IN
V
OUT
=
25˚C, and those with boldface type apply over full Operating Tempera-
A
≤ 1A 1.230 V
LOAD
=
0.5A 74
=
≤ 8V 1.193/1.180 V(min)
OUT
12V, I
LOAD
Programmed for 3V. See Circuit of
Figure 3
Typical Limit
(Note 6) (Note 7)
1.267/1.280 V(max)
(Limits)
%
LM2825H-ADJ Electrical Characteristics (Note 5)
Specifications with standard type face are for T
Figure 3
Range. Test Circuit
.
Symbol Parameter Conditions LM2825H-ADJ Units
V
Adjust Pin Voltage 9V ≤ VIN≤ 40V, 0.1A ≤ I
ADJ
7V ≤ V
η Efficiency V
=
IN
V
OUT
See Circuit of
=
25˚C, and those with boldface type apply over full Operating Temperature
A
Typical Limit
(Note 6) (Note 7)
≤ 0.55A 1.230 V
≤ 15V 1.193/1.180 V(min)
OUT
LOAD
1.267/1.280 V(max)
24V, I
=
0.5A 87
LOAD
Programmed for 12V.
Figure 3
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(Limits)
%
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All Output Voltage Versions Electrical Characteristics
Specifications with standard type face are for T
=
less otherwise specified, V
12V for 3.3V, 5.0V and ADJ versions, V
IN
Symbol Parameter Conditions LM2825-XX Units
I
CL
I
Q
DC Output Current
Limit
Operating Quiescent
Current
R
L
SD/SS Pin=3.1V 5 mA
(Note 8) 10 mA(max)
I
STBY
Standby Quiescent
Current
SD/SS Pin=0V 65 µA
(Note 8) 200 µA(max)
I
ADJ
f
O
θ
JA
Adjust Pin Bias Current Adjustable Versions Only, V
Oscillator Frequency (Note 9) 150 kHz
Thermal Resistance Junction to Ambient (Note 10) 30 ˚C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit
V
SD
Shutdown Threshold
Voltage
Low (Shutdown Mode) 0.6 V(max)
High (Soft-start Mode) 2.0 V(min)
V
SS
I
SD
Soft-start Voltage V
Shutdown Current V
OUT
V
OUT
SHUTDOWN
(Note 8) 10 µA(max)
I
SS
Soft-start Current V
SOFT-START
(Note 8) 5 µA(max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 5 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 4: When the LM2825 is used as shown in
Note 5: When the LM2825 is used as shown in
Note 6: Typical numbers are at 25˚C and represent the most likely norm.
Note 7: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face) when output current is limited to the value given
in the temperature derating curves. Seethe application section for curves. All limits at temperature extremes are guaranteed using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 8: I
Note 9: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current over-
load.
Note 10: Junction to ambient thermal resistance (no external heat sink) for the DIP-24 package with the leads soldered to a printed circuit board with (1 oz.) copper
area of approximately 2 in
LOAD
=
0A.
2
.
Figure 2
Figure 3
=
25˚C, and those with boldface type apply over full Operating Range. Un-
A
=
24V for 12V and H-ADJ versions, I
IN
LOAD
=
Typical Limit
(Note 6) (Note 7)
=
0Ω 1.4 A
1.2 A(min)
2.4 A(max)
=
1.3V 6 nA
FB
50/100 nA(max)
Figure 2
1.3 V
=
20%of Nominal Output Voltage 2 V
=
100%of Nominal Output Voltage 3
=
0.5V
=
2.5V 1.6 µA
test circuit, system performance will be as shown in Electrical Characteristics.
test circuit, system performance will be as shown in Electrical Characteristics.
5µA
100 mA.
(Limits)
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Page 5
Typical Performance Characteristics (Circuits of
=
V
12V for 3.3V, 5.0V and ADJ versions, V
IN
Normalized
Output Voltage
=
24V for 12V and H-ADJ versions, I
IN
Efficiency
Figure 2
and
Figure 3
LOAD
Dropout Voltage
) Unless otherwise specified,
=
100 mA, T
=
25˚C
A
Line Regulation
Operating
Quiescent Current
DS012661-3
DS012661-6
DS012661-9
Load Regulation
Shutdown
Quiescent Current
DS012661-4
DS012661-7
DS012661-10
DS012661-5
Output
Ripple Voltage
DS012661-8
Switching Frequency
DS012661-11
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Typical Performance Characteristics (Circuits of
=
V
12V for 3.3V, 5.0V and ADJ versions, V
IN
=
24V for 12V and H-ADJ versions, I
IN
Figure 2
and
Figure 3
LOAD
) Unless otherwise specified,
=
100 mA, T
=
25˚C (Continued)
A
Soft-start
Shutdown /Soft-start
Current
DS012661-12
Switch Current
Limit
DS012661-28
Load Transient Response for Continuous Mode
=
V
20V, V
IN
OUT
=
=
5V, I
250 mA to 750 mA
L
Soft-start Response
DS012661-14
DS012661-13
Adjust Pin
Bias Current
DS012661-29
Load Transient Response for Discontinuous Mode
=
V
20V, V
IN
OUT
=
=
5V, I
40 mA to 140 mA
L
A: Output Voltage 100 mV/div (AC)
B: 250 mA to 750 mA Load Pulse
Horizontal Time Base: 200 µs/div
DS012661-23
FIGURE 1. Typical Load Transient Response
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A: Output Voltage 100 mV/div (AC)
B: 40 mA to 140 mA Load Pulse
Horizontal Time Base: 200 µs/div
DS012661-24
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Test Circuit
*
Optional—Required if package is more than 6" away from main filter or bypass capacitor.
*
*Optional Soft-start Capacitor
=
40V (max)
V
IN
=
V
OUT
3.3V or 5V
@
1A or 12V@0.75A
FIGURE 2. Standard Test Circuit
(Fixed Output Voltage Versions)
*
Optional—Required if package is more than 6" away from main filter or bypass capacitor.
*
*Optional Soft-start Capacitor
***
Optional—See Application Information.
=
40V (max)
V
IN
=
1.23V to 8V (LM2825-ADJ)
V
OUT
7V to 15V (LM2825H-ADJ)
=
(See derating curves)
I
I
LOAD
MAX
FIGURE 3. Standard Test Circuit
(Adjustable Output Voltage Versions)
Application Information
Select R2 with the following equation.
DS012661-19
DS012661-30
PROGRAMMING OUTPUT VOLTAGE
Figure 3
(Selecting R1 and R2 as shown in
)
The LM2825 is available in two adjustable output versions.
The LM2825-ADJ has been optimized for output voltages
between 1.23V and 8V, while the LM2825H-ADJ covers the
output voltage range of 7V to 15V. Both adjustable versions
are set in the following way.
Select a value for R1 between 240Ω and 1.5 kΩ. The lower
resistor values minimize noise pickup at the sensitive adjust
pin. (For lowest temperature coefficient and the best stability
with time, use 1%metal film resistors.)
When programming V
greater than V
OUT
, keep in mind that VINmust be
OUT
+ 2V for proper operation.
OPTIONAL EXTERNAL COMPONENTS
SOFT-START CAPACITOR
: A capacitor on this pin provides the regulator with a
C
SS
Soft-start feature (slow start-up). The current drawn from the
source starts out at a low average level with narrow pulses,
and ramps up in a controlled manner as the pulses expand
to their steady-state width. This reduces the startup current
considerably,and delays and slows down the output voltage
rise time.
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Page 8
Application Information (Continued)
It is especially useful in situations where the input power
source is limited in the amount of current it can deliver, since
you avoid loading down this type of power supply.
Under some operating conditions, a Soft-start capacitor is
required for proper operation.
voltage and ambient temperature conditions for which a
Soft-start capacitor may be required.
This curve is typical for full guaranteed output current and
can be used as a guideline.As the output current decreases,
the operating area requiring a Soft-start capacitor decreases. Capacitor values between 0.1 µF and 1 µF are recommended. Tantalum or ceramic capacitors are appropriate
for this application.
INPUT CAPACITOR
C
: An optional input capacitor is required if the package is
IN
more than 6" away from the main filter or bypass capacitor.A
low ESR aluminum or tantalum bypass capacitor is recommended between the input pin and ground to prevent large
voltage transients from appearing at the input. In addition, to
be conservative, the RMS current rating of the input capacitor should be selected to be at least
With a 1A load, a capacitor with a RMS current rating of at
least 500 mA is recommended.
The voltage rating should be approximately 1.25 times the
maximum input voltage. With a nominal input voltage of 12V,
an aluminum electrolytic capacitor (Panasonic HFQ series or
Nichicon PL series or equivalent) with a voltage rating
greater than 15V (1.25 x V
Solid tantalum input capacitors should only be used where
the input source is impedance current limited. High dV/dt applied at the input can cause excessive charge current
through low ESR tantalum capacitors. This high charge current can result in shorting within the capacitor. It is recommended that they be surge current tested by the manufacturer.The TPS series available from AVX, and the 593D series
from Sprague are both surge current tested.
Use caution when using ceramic capacitors for input bypassing, because it may cause ringing at the V
LOWERING OUTPUT RIPPLE
When using the adjustable parts, one can achieve lower output ripple voltage by shorting a resistor internal to the
LM2825. However, if this resistor is shorted, a feed forward
capacitor must be used to keep the regulator stable. For this
reason, this resistor must be left open on all of the fixed output voltage versions or instability will result. See the feed forward capacitor selection below. Shorting the internal resistor
is accomplished by shorting pins 8 and 9 on the LM2825,
and will typically reduce output ripple by 25 to 33%.
FEED FORWARD CAPACITOR SELECTION (C
When using an adjustable part and pins 8 and 9 are shorted
to reduce output ripple, a feed forward capacitor is required.
This capacitor is typically between 680 pF and 2700 pF. The
table of
Figure 4
shows the value for CFFfor a given output
voltage and feedback resistor R
Figure 5
indicates the input
1
⁄2the DC load current.
) would be needed.
IN
(R1=1kΩ).
2
pin.
IN
)
FF
V
OUT
R2 C
FF
LM2825-ADJ
2 630 N/A
3 1.43k N/A
4 2.26k 2700 pF
5 3.09k 2700 pF
6 3.92k 2200 pF
7 4.75k 1800 pF
8 5.49k 1500 pF
LM2825H-ADJ
7 4.75k 2700 pF
8 5.49k 2200 pF
9 6.34k 1800 pF
10 7.15k 1500 pF
11 8.06k 1000 pF
12 8.87k 820 pF
13 9.53k 680 pF
14 10.5k 680 pF
15 11.3k 680 pF
FIGURE 4. C
Selection Table
FF
SHUTDOWN
The circuit shown in
Figure 10
shows 2 circuits for the
Shutdown/Soft-start feature using different logic signals for
shutdown and using a 0.1 µF Soft-start capacitor.
THERMAL CONSIDERATIONS
The LM2825 is available in a 24-pin through hole DIP. The
package is molded plastic with a copper lead frame. When
the package is soldered to the PC board, the copper and the
board are the heat sink for the LM2825.
DS012661-22
FIGURE 5. Usage of the Soft-start Capacitor
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Page 9
Application Information (Continued)
OUTPUT CURRENT DERATING FOR T
=
−40˚C to −25˚C AND T
J
At the lower temperature extremes, the switch current limit drops off sharply. As a result, a lower output current is available in this
Figure 6
and
Figure 7
temperature range. See
for the typical available output current at these temperature ranges.
FIGURE 6. LM2825 Output Current Derating for T
=
−25˚C to 0˚C
J
=
−40˚C to −25˚C
J
DS012661-32
FIGURE 7. LM2825 Output Current Derating for T
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=
−25˚C to 0˚C
J
DS012661-33
Page 10
Application Information (Continued)
OUTPUT CURRENT DERATING FOR T
Due to the limited switch current, the LM2825 cannot supply the full one ampere output current over the entire input and output
Figure 8
voltage range.
shows the typical available output current for any input and output voltage combination. This applies for
all output voltage versions.
FIGURE 8. LM2825 Output Current Derating for T
OUTPUT CURRENT DERATING FOR T
At high these high ambient temperatures, the LM2825 cannot supply the full one ampere over the entire input and output voltage
range. This is due to thermal reasons and
combination. This applies for all output voltage versions.
=
0˚C to 70˚C
A
=
70˚C to 85˚C
A
Figure 9
DS012661-34
=
0˚C to 70˚C
A
shows the typical available output current for any input and output voltage
FIGURE 9. LM2825 Output Current Derating for T
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=
70˚C to 85˚C
A
DS012661-35
Page 11
Application Information (Continued)
FIGURE 10. Typical Circuits Using Shutdown /Soft-start Features
TYPICAL THROUGH HOLE PC BOARD LAYOUT (2X SIZE), SINGLE SIDED, THROUGH HOLE PLATED
DS012661-25
Note: Holes are not shown.
“No Connect Pins” are connected to copper pads for thermal reasons only and must remain electrically isolated.
FIGURE 11. 2X Printed Circuit Board Layout
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DS012661-26
Page 12
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N12, LM2825N-ADJ or LM2825HN-ADJ
24-Lead (0.600" Wide) Molded Dual-In-Line Package
NS Package Number NA24F
LM2825 Integrated Power Supply 1A DC-DC Converter
LIFE SUPPORT POLICY
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1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into
the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
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Corporation
Americas
Tel: 1-800-272-9959
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Email: support@nsc.com
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