NSC LM2825N-12 Integrated power supply 1a dc-dc converter Datasheet

LM2825
Integrated Power Supply 1A DC-DC Converter
General Description
Features
The LM2825 is a complete 1A DC-DC Buck converter packaged in a 24-lead molded Dual-In-Line integrated circuit
package.
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Contained within the package are all the active and passive
components for a high efficiency 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.
Minimum design time required
3.3V, 5V and 12V fixed output versions
Two adjustable versions allow 1.23V to 15V outputs
Wide input voltage range, up to 40V
Low-power standby mode, IQ typically 65 µA
High efficiency, typically 80%
± 4% output voltage tolerance
Excellent line and load regulation
TTL shutdown capability/programmable Soft-start
Thermal shutdown and current limit protection
−40˚C to +85˚C ambient temperature range
Highlights
Applications
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/in3
n 24-pin DIP package profile (1.25 x 0.54 x 0.26 inches)
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Simple high-efficiency step-down (buck) regulator
On-card switching regulators
Efficient pre-regulator for linear regulators
Distributed power systems
DC/DC module replacement
Connection Diagram
DS012661-27
Standard Application
(Fixed output voltage versions)
DS012661-2
“NC (Do not use)” pins: See Figure 11.
Top View
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
Ordering Information
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N-12,
LM2825N-ADJ or LM2825HN-ADJ
See NS Package Number NA24F
30 dB µV/m
230. . . .1000 MHz
37 dB µV/m
1. . . .10 GHz
46 dB µV/m
© 1997 National Semiconductor Corporation
DS012661
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LM2825 Integrated Power Supply 1A DC-DC Converter
May 1997
Absolute Maximum Ratings
(Note 1)
ESD Susceptibility
Human Body Model (Note 3)
Lead Temperature (Soldering 10 sec.)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Input Supply (VIN)
SD/SS Pin Input Voltage (Note 2)
Output Pin Voltage
(3.3V, 5.0V and ADJ)
(12V and H-ADJ)
ADJ Pin Voltage (ADJ, H-ADJ only)
Power Dissipation
Storage Temperature Range
2 kV
260˚C
Operating Ratings
+45V
6V
−40˚C ≤ TA ≤ +85˚C
−40˚C ≤ TJ ≤ +125˚C
4.75V to 40V
7V to 40V
15V to 40V
4.5V to 40V
Ambient Temperature Range
Junction Temperature Range
Input Supply Voltage (3.3V version)
Input Supply Voltage (5V version)
Input Supply Voltage (12V version)
Input Supply Voltage (-ADJ, H-ADJ)
−1V ≤ V ≤ 9V
−1V ≤ V ≤ 16V
−0.3V ≤ V ≤ 25V
Internally Limited
−40˚C to +125˚C
LM2825-3.3 Electrical Characteristics
(Note 4)
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2.
Symbol
VOUT
Parameter
Output Voltage
4.75V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
Line Regulation
4.75V ≤ VIN ≤ 40V
ILOAD = 100 mA
Load Regulation
0.1A ≤ ILOAD ≤ 1A
VIN = 12V
VIN = 12V, ILOAD = 1A
VIN = 12V, ILOAD = 0.5A
Output Ripple Voltage
η
Conditions
Efficiency
LM2825-3.3
Typical
Limit
(Note 6)
(Note 7)
3.3
Units
(Limits)
V
3.168/3.135
V(min)
3.432/3.465
V(max)
1.5
mV
8
mV
40
mV p-p
75
%
LM2825-5.0 Electrical Characteristics
(Note 4)
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2.
Symbol
VOUT
Parameter
Output Voltage
7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
Line Regulation
7V ≤ VIN ≤ 40V
ILOAD = 100 mA
Load Regulation
0.1A ≤ ILOAD ≤ 1A
VIN = 12V
VIN = 12V, ILOAD = 1A
VIN = 12V, ILOAD = 0.5A
Output Ripple Voltage
η
Conditions
Efficiency
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LM2825-5.0
Typical
Limit
(Note 6)
(Note 7)
5.0
Units
(Limits)
V
4.800/4.750
V(min)
5.200/5.250
V(max)
2.7
mV
8
mV
40
mV p-p
80
%
LM2825-12 Electrical Characteristics (Note 4)
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2.
Symbol
VOUT
η
Parameter
Output Voltage
Conditions
LM2825-12
Typical
Limit
(Note 6)
(Note 7)
15V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.75A
Units
(Limits)
12.0
V
11.52/11.40
V(min)
12.48/12.60
V(max)
Line Regulation
15V ≤ VIN ≤ 40V
ILOAD = 100 mA
8.5
mV
Load Regulation
12
mV
Output Ripple Voltage
0.1A ≤ ILOAD ≤ 0.75A
VIN = 24V
VIN = 24V, ILOAD = 1A
100
mV p-p
Efficiency
VIN = 24V, ILOAD = 0.5A
87
%
LM2825-ADJ Electrical Characteristics (Note 5)
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 3.
Symbol
VADJ
Parameter
Adjust Pin Voltage
Conditions
LM2825-ADJ
4.5V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
Typical
Limit
(Note 6)
(Note 7)
1.230
1.23V ≤ VOUT ≤ 8V
η
Efficiency
Units
(Limits)
VIN = 12V, ILOAD = 0.5A
V
1.193/1.180
V(min)
1.267/1.280
V(max)
%
74
VOUT Programmed for 3V. See Circuit of Figure 3
LM2825H-ADJ Electrical Characteristics (Note 5)
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature
Range. Test Circuit Figure 3.
Symbol
VADJ
Parameter
Adjust Pin Voltage
Conditions
9V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.55A
LM2825H-ADJ
Typical
Limit
(Note 6)
(Note 7)
1.230
7V ≤ VOUT ≤ 15V
η
Efficiency
VIN = 24V, ILOAD = 0.5A
87
Units
(Limits)
V
1.193/1.180
V(min)
1.267/1.280
V(max)
%
VOUT Programmed for 12V.
See Circuit of Figure 3
3
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All Output Voltage Versions Electrical Characteristics
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Range. Unless otherwise specified, VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA.
Symbol
ICL
Parameter
DC Output Current
Limit
IQ
Operating Quiescent
Current
ISTBY
Standby Quiescent
Current
IADJ
Adjust Pin Bias Current
Conditions
RL = 0Ω
LM2825-XX
Typical
Limit
(Note 6)
(Note 7)
1.4
SD/SS Pin = 3.1V
5
(Note 8)
SD/SS Pin = 0V
65
A
1.2
A(min)
2.4
A(max)
mA
10
mA(max)
µA
(Note 8)
Adjustable Versions Only, VFB = 1.3V
Units
(Limits)
200
µA(max)
50/100
nA(max)
6
nA
fO
Oscillator Frequency
(Note 9)
150
kHz
θJA
Thermal Resistance
Junction to Ambient (Note 10)
30
˚C/W
1.3
V
SHUTDOWN/SOFT-START CONTROL Test Circuit Figure 2
VSD
VSS
ISD
Shutdown Threshold
Voltage
Soft-start Voltage
Shutdown Current
Low (Shutdown Mode)
0.6
V(max)
High (Soft-start Mode)
VOUT = 20% of Nominal Output Voltage
VOUT = 100% of Nominal Output Voltage
2.0
V(min)
2
VSHUTDOWN = 0.5V
5
(Note 8)
ISS
Soft-start Current
VSOFT-START = 2.5V
V
3
µA
10
µA(max)
5
µA(max)
1.6
(Note 8)
µA
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 Figure 2 test circuit, system performance will be as shown in Electrical Characteristics.
Note 5: When the LM2825 is used as shown in Figure 3 test circuit, system performance will be as shown in Electrical Characteristics.
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. See the 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: ILOAD = 0A.
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 overload.
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 in2.
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Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified,
VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA, TA = 25˚C
Efficiency
Normalized
Output Voltage
Dropout Voltage
DS012661-5
DS012661-4
DS012661-3
Line Regulation
Load Regulation
Output
Ripple Voltage
DS012661-7
DS012661-6
DS012661-8
Operating
Quiescent Current
Shutdown
Quiescent Current
Switching Frequency
DS012661-11
DS012661-9
DS012661-10
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Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified,
VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA, TA = 25˚C (Continued)
Shutdown /Soft-start
Current
Soft-start
Soft-start Response
DS012661-12
DS012661-14
DS012661-13
Switch Current
Limit
Adjust Pin
Bias Current
DS012661-29
DS012661-28
Load Transient Response for Continuous Mode
VIN = 20V, VOUT = 5V, IL = 250 mA to 750 mA
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V, IL = 40 mA to 140 mA
DS012661-23
DS012661-24
A: Output Voltage 100 mV/div (AC)
B: 250 mA to 750 mA Load Pulse
Horizontal Time Base: 200 µs/div
A: Output Voltage 100 mV/div (AC)
B: 40 mA to 140 mA Load Pulse
Horizontal Time Base: 200 µs/div
FIGURE 1. Typical Load Transient Response
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Test Circuit
DS012661-19
*Optional—Required if package is more than 6" away from main filter or bypass capacitor.
**Optional Soft-start Capacitor
VIN = 40V (max)
VOUT = 3.3V or 5V @ 1A or 12V @ 0.75A
FIGURE 2. Standard Test Circuit
(Fixed Output Voltage Versions)
DS012661-30
*Optional—Required if package is more than 6" away from main filter or bypass capacitor.
**Optional Soft-start Capacitor
***Optional—See Application Information.
VIN = 40V (max)
VOUT = 1.23V to 8V (LM2825-ADJ)
7V to 15V (LM2825H-ADJ)
ILOAD = IMAX (See derating curves)
FIGURE 3. Standard Test Circuit
(Adjustable Output Voltage Versions)
Application Information
Select R2 with the following equation.
PROGRAMMING OUTPUT VOLTAGE
(Selecting R1 and R2 as shown in Figure 3)
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.
When programming VOUT, keep in mind that VIN must be
greater than VOUT + 2V for proper operation.
OPTIONAL EXTERNAL COMPONENTS
SOFT-START CAPACITOR
CSS: A capacitor on this pin provides the regulator with a
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.
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.)
7
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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. Figure 5 indicates the input
voltage and ambient temperature conditions for which a
Soft-start capacitor may be required.
VOUT
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.
R2
CFF
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
INPUT CAPACITOR
CIN: An optional input capacitor is required if the package is
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 1⁄2 the DC load current.
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 VIN) would be needed.
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 VIN pin.
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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. CFF Selection Table
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.
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 (CFF)
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 CFF for a given output
voltage and feedback resistor R2 (R1 = 1 kΩ).
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DS012661-22
FIGURE 5. Usage of the Soft-start Capacitor
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Application Information
(Continued)
OUTPUT CURRENT DERATING FOR TJ = −40˚C to −25˚C AND TJ = −25˚C to 0˚C
At the lower temperature extremes, the switch current limit drops off sharply. As a result, a lower output current is available in this
temperature range. See Figure 6 and Figure 7 for the typical available output current at these temperature ranges.
DS012661-32
FIGURE 6. LM2825 Output Current Derating for TJ = −40˚C to −25˚C
DS012661-33
FIGURE 7. LM2825 Output Current Derating for TJ = −25˚C to 0˚C
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Application Information
(Continued)
OUTPUT CURRENT DERATING FOR TA = 0˚C to 70˚C
Due to the limited switch current, the LM2825 cannot supply the full one ampere output current over the entire input and output
voltage range. Figure 8 shows the typical available output current for any input and output voltage combination. This applies for
all output voltage versions.
DS012661-34
FIGURE 8. LM2825 Output Current Derating for TA = 0˚C to 70˚C
OUTPUT CURRENT DERATING FOR TA = 70˚C to 85˚C
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 Figure 9 shows the typical available output current for any input and output voltage
combination. This applies for all output voltage versions.
DS012661-35
FIGURE 9. LM2825 Output Current Derating for TA = 70˚C to 85˚C
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Application Information
(Continued)
DS012661-25
FIGURE 10. Typical Circuits Using Shutdown /Soft-start Features
TYPICAL THROUGH HOLE PC BOARD LAYOUT (2X SIZE), SINGLE SIDED, THROUGH HOLE PLATED
DS012661-26
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
11
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LM2825 Integrated Power Supply 1A DC-DC Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
24-Lead (0.600" Wide) Molded Dual-In-Line Package
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N12, LM2825N-ADJ or LM2825HN-ADJ
NS Package Number NA24F
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