LM2825-12 [NSC]

Integrated Power Supply 1A DC-DC Converter(633.82 k) ; 集成电源1A DC - DC转换器（ 633.82 K）\n


型号：	LM2825-12
厂家：	National Semiconductor
描述：	Integrated Power Supply 1A DC-DC Converter(633.82 k) 集成电源1A DC - DC转换器（ 633.82 K）\n 转换器
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, I_Qtypically 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.

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

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 (V_IN

)

+45V

SD/SS Pin Input Voltage (Note 2)

Output Pin Voltage

−40˚C ≤ T_A≤ +85˚C

−40˚C ≤ T_J≤ +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 T_A25˚C, and those with boldface type apply over full Operating Tempera-

ture Range. Test Circuit Figure 2.

Symbol

Parameter

Conditions

4.75V ≤ V_IN≤ 40V, 0.1A ≤ I_LOAD≤ 1A

4.75V ≤ V_IN≤ 40V

LM2825-3.3

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

V_OUT

Output Voltage

3.3

3.168/3.135

3.432/3.465

V(min)

V(max)

Line Regulation

Load Regulation

1.5

I_LOAD100 mA

0.1A ≤ I_LOAD≤ 1A

V_IN12V

Output Ripple Voltage

Efficiency

V_IN12V, I_LOAD1A

mV p-p

= =

V_IN12V, I_LOAD0.5A

LM2825-5.0 Electrical Characteristics (Note 4)

Specifications with standard type face are for T_A25˚C, and those with boldface type apply over full Operating Tempera-

ture Range. Test Circuit Figure 2.

Symbol

Parameter

Conditions

7V ≤ V_IN≤ 40V, 0.1A ≤ I_LOAD≤ 1A

7V ≤ V_IN≤ 40V

LM2825-5.0

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

V_OUT

Output Voltage

5.0

4.800/4.750

5.200/5.250

V(min)

V(max)

Line Regulation

Load Regulation

2.7

I_LOAD100 mA

0.1A ≤ I_LOAD≤ 1A

V_IN12V

Output Ripple Voltage

Efficiency

V_IN12V, I_LOAD1A

mV p-p

= =

V_IN12V, I_LOAD0.5A

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LM2825-12 Electrical Characteristics (Note 4)

Specifications with standard type face are for T_A25˚C, and those with boldface type apply over full Operating Tempera-

ture Range. Test Circuit Figure 2.

Symbol

Parameter

Conditions

15V ≤ V_IN≤ 40V, 0.1A ≤ I_LOAD≤ 0.75A

15V ≤ V_IN≤ 40V

LM2825-12

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

V_OUT

Output Voltage

12.0

11.52/11.40

12.48/12.60

V(min)

V(max)

Line Regulation

Load Regulation

8.5

I_LOAD100 mA

0.1A ≤ I_LOAD≤ 0.75A

V_IN24V

Output Ripple Voltage

Efficiency

V_IN24V, I_LOAD1A

100

mV p-p

= =

V_IN24V, I_LOAD0.5A

LM2825-ADJ Electrical Characteristics (Note 5)

Specifications with standard type face are for T_A25˚C, and those with boldface type apply over full Operating Tempera-

ture Range. Test Circuit Figure 3.

Symbol

V_ADJ

Parameter

Adjust Pin Voltage

Efficiency

Conditions

LM2825-ADJ

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

4.5V ≤ V_IN≤ 40V, 0.1A ≤ I_LOAD≤ 1A

1.23V ≤ V_OUT≤ 8V

1.230

1.193/1.180

1.267/1.280

V(min)

V(max)

V_IN12V, I_LOAD0.5A

V_OUTProgrammed for 3V. See Circuit of Figure 3

LM2825H-ADJ Electrical Characteristics (Note 5)

Specifications with standard type face are for T_A25˚C, and those with boldface type apply over full Operating Temperature

Range. Test Circuit Figure 3.

Symbol

V_ADJ

Parameter

Adjust Pin Voltage

Efficiency

Conditions

LM2825H-ADJ

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

9V ≤ V_IN≤ 40V, 0.1A ≤ I_LOAD≤ 0.55A

7V ≤ V_OUT≤ 15V

1.230

1.193/1.180

1.267/1.280

V(min)

V(max)

V_IN24V, I_LOAD0.5A

V_OUTProgrammed for 12V.

See Circuit of Figure 3

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All Output Voltage Versions Electrical Characteristics

Specifications with standard type face are for T_A25˚C, and those with boldface type apply over full Operating Range. Un-

less otherwise specified, V_IN12V for 3.3V, 5.0V and ADJ versions, V_IN24V for 12V and H-ADJ versions, I_LOAD100 mA.

Symbol

Parameter

Conditions

LM2825-XX

Units

(Limits)

Typical

Limit

(Note 6)

(Note 7)

I_CL

DC Output Current

Limit

R_L0Ω

1.4

1.2

2.4

A(min)

A(max)

I_Q

Operating Quiescent

Current

SD/SS Pin 3.1V

(Note 8)

mA(max)

µA

I_STBY

Standby Quiescent

Current

SD/SS Pin 0V

(Note 8)

200

µA(max)

Adjust Pin Bias Current Adjustable Versions Only, V_FB1.3V

I_ADJ

50/100

nA(max)

kHz

f_O

Oscillator Frequency

Thermal Resistance

(Note 9)

150

θ_JA

Junction to Ambient (Note 10)

˚C/W

SHUTDOWN/SOFT-START CONTROL Test Circuit Figure 2

V_SD

Shutdown Threshold

Voltage

1.3

Low (Shutdown Mode)

High (Soft-start Mode)

0.6

2.0

V(max)

V(min)

V_SS

I_SD

I_SS

Soft-start Voltage

Shutdown Current

Soft-start Current

V_OUT20% of Nominal Output Voltage

V_OUT100% of Nominal Output Voltage

V_SHUTDOWN0.5V

µA

(Note 8)

µA(max)

µA

V_SOFT-START2.5V

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:

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

area of approximately 2 in .

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Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified,

V_IN12V for 3.3V, 5.0V and ADJ versions, V_IN24V for 12V and H-ADJ versions, I_LOAD100 mA, T_A25˚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

DS012661-11

DS012661-9

DS012661-10

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Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified,

V_IN12V for 3.3V, 5.0V and ADJ versions, V_IN24V for 12V and H-ADJ versions, I_LOAD100 mA, T_A25˚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

V_IN20V, V_OUT5V, I_L250 mA to 750 mA

V_IN20V, V_OUT5V, I_L40 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

40V (max)

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.

40V (max)

1.23V to 8V (LM2825-ADJ)

7V to 15V (LM2825H-ADJ)

OUT

(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 V_OUT, keep in mind that V_INmust be

greater than V_OUT+ 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

C_SS: 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.)

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Application Information (Continued)

V_OUT

LM2825-ADJ

630

C_FF

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.

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

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

2700 pF

2200 pF

1800 pF

1500 pF

1000 pF

820 pF

680 pF

5.49k

INPUT CAPACITOR

6.34k

_IN: An optional input capacitor is required if the package is

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-

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. C_FFSelection 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 V_IN) 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 V_INpin.

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 (C_FF

)

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 C_FFfor 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 T_J−40˚C to −25˚C AND T_J−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 T_J−40˚C to −25˚C

DS012661-33

FIGURE 7. LM2825 Output Current Derating for T_J−25˚C to 0˚C

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Application Information (Continued)

OUTPUT CURRENT DERATING FOR T_A0˚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 T_A0˚C to 70˚C

OUTPUT CURRENT DERATING FOR T_A70˚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 T_A70˚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

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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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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DE-

VICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMI-

CONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or sys-

tems which, (a) are intended for surgical implant into

the body, or (b) support or sustain life, and whose fail-

ure 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.

2. A critical component in any component of a life support

device or system whose failure to perform can be rea-

sonably expected to cause the failure of the life support

device or system, or to affect its safety or effectiveness.

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Corporation

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Europe

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Hong Kong Ltd.

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

LM2825-12 [NSC]

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