LM2825 [NSC]
Integrated Power Supply 1A DC-DC Converter; 集成电源1A DC -DC转换器型号: | LM2825 |
厂家: | National Semiconductor |
描述: | Integrated Power Supply 1A DC-DC Converter |
文件: | 总12页 (文件大小:637K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
May 1997
LM2825
Integrated Power Supply 1A DC-DC Converter
General Description
The LM2825 is a complete 1A DC-DC Buck converter pack-
aged in a 24-lead molded Dual-In-Line integrated circuit
package.
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, IQ typically 65 µA
n High efficiency, typically 80%
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 electri-
cal specifications.
±
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
Self-contained, this converter is also fully protected from out-
put fault conditions, such as excessive load current, short
circuits, or excessive temperatures.
Applications
n Simple high-efficiency step-down (buck) regulator
n On-card switching regulators
Highlights
n No external components required (fixed output voltage
versions)
n Efficient pre-regulator for linear regulators
n Distributed power systems
n DC/DC module replacement
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)
Connection Diagram
DS012661-27
Standard Application
(Fixed output voltage versions)
DS012661-2
“NC (Do not use)” pins: See Figure 11.
Top View
DS012661-1
Ordering Information
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N-12,
LM2825N-ADJ or LM2825HN-ADJ
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.
See NS Package Number NA24F
30. . . .230 MHz
230. . . .1000 MHz
1. . . .10 GHz
30 dB µV/m
37 dB µV/m
46 dB µV/m
© 1997 National Semiconductor Corporation
DS012661
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Susceptibility
Human Body Model (Note 3)
Lead Temperature (Soldering 10 sec.)
2 kV
260˚C
Operating Ratings
Ambient Temperature Range
Maximum Input Supply (VIN
)
+45V
6V
SD/SS Pin Input Voltage (Note 2)
Output Pin Voltage
−40˚C ≤ TA ≤ +85˚C
−40˚C ≤ TJ ≤ +125˚C
4.75V to 40V
Junction Temperature Range
(3.3V, 5.0V and ADJ)
−1V ≤ V ≤ 9V
−1V ≤ V ≤ 16V
Input Supply Voltage (3.3V version)
Input Supply Voltage (5V version)
Input Supply Voltage (12V version)
Input Supply Voltage (-ADJ, H-ADJ)
(12V and H-ADJ)
7V to 40V
ADJ Pin Voltage (ADJ, H-ADJ only)
Power Dissipation
−0.3V ≤ V ≤ 25V
Internally Limited
−40˚C to +125˚C
15V to 40V
4.5V to 40V
Storage Temperature Range
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 Tempera-
ture Range. Test Circuit Figure 2.
Symbol
Parameter
Conditions
4.75V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
4.75V ≤ VIN ≤ 40V
LM2825-3.3
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
VOUT
Output Voltage
3.3
V
3.168/3.135
3.432/3.465
V(min)
V(max)
mV
Line Regulation
Load Regulation
1.5
8
=
ILOAD 100 mA
0.1A ≤ ILOAD ≤ 1A
mV
=
VIN 12V
=
=
Output Ripple Voltage
Efficiency
VIN 12V, ILOAD 1A
40
75
mV p-p
%
= =
VIN 12V, ILOAD 0.5A
η
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 Tempera-
ture Range. Test Circuit Figure 2.
Symbol
Parameter
Conditions
7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
7V ≤ VIN ≤ 40V
LM2825-5.0
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
VOUT
Output Voltage
5.0
V
4.800/4.750
5.200/5.250
V(min)
V(max)
mV
Line Regulation
Load Regulation
2.7
8
=
ILOAD 100 mA
0.1A ≤ ILOAD ≤ 1A
mV
=
VIN 12V
=
=
Output Ripple Voltage
Efficiency
VIN 12V, ILOAD 1A
40
80
mV p-p
%
= =
VIN 12V, ILOAD 0.5A
η
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2
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 Tempera-
ture Range. Test Circuit Figure 2.
Symbol
Parameter
Conditions
15V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.75A
15V ≤ VIN ≤ 40V
LM2825-12
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
VOUT
Output Voltage
12.0
V
11.52/11.40
12.48/12.60
V(min)
V(max)
mV
Line Regulation
Load Regulation
8.5
12
=
ILOAD 100 mA
0.1A ≤ ILOAD ≤ 0.75A
mV
=
VIN 24V
=
=
Output Ripple Voltage
Efficiency
VIN 24V, ILOAD 1A
100
87
mV p-p
%
= =
VIN 24V, ILOAD 0.5A
η
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 Tempera-
ture Range. Test Circuit Figure 3.
Symbol
VADJ
η
Parameter
Adjust Pin Voltage
Efficiency
Conditions
LM2825-ADJ
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
4.5V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
1.23V ≤ VOUT ≤ 8V
1.230
V
1.193/1.180
1.267/1.280
V(min)
V(max)
%
=
=
VIN 12V, ILOAD 0.5A
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
η
Parameter
Adjust Pin Voltage
Efficiency
Conditions
LM2825H-ADJ
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
9V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.55A
7V ≤ VOUT ≤ 15V
1.230
V
1.193/1.180
1.267/1.280
V(min)
V(max)
%
=
=
VIN 24V, ILOAD 0.5A
VOUT Programmed for 12V.
See Circuit of Figure 3
87
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. Un-
=
=
=
less otherwise specified, VIN 12V for 3.3V, 5.0V and ADJ versions, VIN 24V for 12V and H-ADJ versions, ILOAD 100 mA.
Symbol
Parameter
Conditions
LM2825-XX
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
=
ICL
DC Output Current
Limit
RL 0Ω
1.4
A
1.2
2.4
A(min)
A(max)
mA
=
IQ
Operating Quiescent
Current
SD/SS Pin 3.1V
5
65
6
(Note 8)
10
mA(max)
µA
=
ISTBY
Standby Quiescent
Current
SD/SS Pin 0V
(Note 8)
200
µA(max)
nA
=
Adjust Pin Bias Current Adjustable Versions Only, VFB 1.3V
IADJ
50/100
nA(max)
kHz
fO
Oscillator Frequency
Thermal Resistance
(Note 9)
150
30
θJA
Junction to Ambient (Note 10)
˚C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit Figure 2
VSD
Shutdown Threshold
Voltage
1.3
V
Low (Shutdown Mode)
High (Soft-start Mode)
0.6
2.0
V(max)
V(min)
V
=
VSS
ISD
ISS
Soft-start Voltage
Shutdown Current
Soft-start Current
VOUT 20% of Nominal Output Voltage
2
3
5
=
VOUT 100% of Nominal Output Voltage
=
VSHUTDOWN 0.5V
µA
(Note 8)
10
5
µA(max)
µA
=
VSOFT-START 2.5V
1.6
(Note 8)
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 in-
tended 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).
=
0A.
Note 8:
I
LOAD
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
2
area of approximately 2 in .
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4
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
Normalized
Efficiency
Dropout Voltage
Output Voltage
DS012661-5
DS012661-4
DS012661-3
Line Regulation
Load Regulation
Output
Ripple Voltage
DS012661-6
DS012661-7
DS012661-8
Operating
Shutdown
Switching Frequency
Quiescent Current
Quiescent Current
DS012661-11
DS012661-9
DS012661-10
5
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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)
Soft-start
Shutdown /Soft-start
Current
Soft-start Response
DS012661-12
DS012661-14
DS012661-13
Switch Current
Limit
Adjust Pin
Bias Current
DS012661-28
DS012661-29
Load Transient Response for Continuous Mode
Load Transient Response for Discontinuous Mode
=
=
=
=
=
=
VIN 20V, VOUT 5V, IL 250 mA to 750 mA
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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6
Test Circuit
DS012661-19
*
Optional—Required if package is more than 6" away from main filter or bypass capacitor.
*Optional Soft-start Capacitor
*
=
V
V
40V (max)
=
IN
OUT
@
@
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.
=
V
V
40V (max)
IN
=
=
1.23V to 8V (LM2825-ADJ)
7V to 15V (LM2825H-ADJ)
OUT
I
I
(See derating curves)
MAX
LOAD
FIGURE 3. Standard Test Circuit
(Adjustable Output Voltage Versions)
Select R2 with the following equation.
Application Information
PROGRAMMING OUTPUT VOLTAGE
(Selecting R1 and R2 as shown in Figure 3)
When programming VOUT, keep in mind that VIN must be
greater than VOUT + 2V for proper operation.
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.
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)
VOUT
R2
LM2825-ADJ
630
CFF
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.
2
3
4
5
6
7
8
N/A
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.
1.43k
N/A
2.26k
2700 pF
2700 pF
2200 pF
1800 pF
1500 pF
3.09k
3.92k
This curve is typical for full guaranteed output current and
can be used as a guideline. As the output current decreases,
4.75k
the operating area requiring
a Soft-start capacitor de-
5.49k
creases. Capacitor values between 0.1 µF and 1 µF are rec-
ommended. Tantalum or ceramic capacitors are appropriate
for this application.
LM2825H-ADJ
4.75k
7
2700 pF
2200 pF
1800 pF
1500 pF
1000 pF
820 pF
680 pF
680 pF
680 pF
8
5.49k
INPUT CAPACITOR
9
6.34k
C
IN: An optional input capacitor is required if the package is
10
11
12
13
14
15
7.15k
more than 6" away from the main filter or bypass capacitor. A
low ESR aluminum or tantalum bypass capacitor is recom-
mended between the input pin and ground to prevent large
voltage transients from appearing at the input. In addition, to
8.06k
8.87k
9.53k
be conservative, the RMS current rating of the input capaci-
1
tor should be selected to be at least
⁄2
the DC load current.
10.5k
With a 1A load, a capacitor with a RMS current rating of at
least 500 mA is recommended.
11.3k
FIGURE 4. CFF Selection Table
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
SHUTDOWN
Nichicon PL series or equivalent) with
a voltage rating
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.
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 ap-
plied at the input can cause excessive charge current
through low ESR tantalum capacitors. This high charge cur-
rent can result in shorting within the capacitor. It is recom-
mended that they be surge current tested by the manufactur-
er.The TPS series available from AVX, and the 593D series
from Sprague are both surge current tested.
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.
Use caution when using ceramic capacitors for input bypass-
ing, because it may cause ringing at the VIN pin.
LOWERING OUTPUT RIPPLE
When using the adjustable parts, one can achieve lower out-
put 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 out-
put voltage versions or instability will result. See the feed for-
ward 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
DS012661-22
FIGURE 5. Usage of the Soft-start Capacitor
=
voltage and feedback resistor R2 (R1 1 kΩ).
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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
9
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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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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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2. A critical component in any component of a life support
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