LM3460-1.2MDC_技术文档

July 2000

LM3460-1.2, -1.5

Precision Controller for GTLp and GTL Bus Termination

General Description

Features

n Precision output (1%)

The LM3460 is a monolithic integrated circuit designed for

precision control of GTLplus and GTL Bus termination. This

controller is available in a tiny SOT23-5 package, and in-

cludes an internally compensated op amp, a bandgap refer-

ence, an NPN output transistor, and voltage setting resistors.

n Output voltage can be adjusted

n Extremely fast transient response in GTLp and GTL bus

termination

n Tiny SOT23-5 package

A trimmed precision bandgap voltage reference utilizes tem-

perature drift curvature correction for excellent voltage stabil-

ity over the operating range. The precision output control en-

ables the termination voltage to maintain tight regulation,

despite fast switching requirements on the bus.

n Output voltage capability for GTL or GTLp

n Low temperature coefficient

Applications

n GTL bus termination (1.2V output 7A)

n GTLp bus termination (1.5V output 7A)

n Adjustable high-current linear regulator

The LM3460 controller is designed to be used with a high

>

current ( 7A) NPN pass transistor to provide the high cur-

rent needed for the bus termination. The wide bandwidth of

the feedback loop provides excellent transient response,

and greatly reduces the output capacitance required, thus

reducing cost and board space requirements.

Connection Diagram and Package Information

5-Lead Outline Package (M5)

Actual Size

DS012603-2

DS012603-3

DS012603-1

*

No internal connection, but should be soldered to PC board for best heat

*

This resistor is not used on the LM3460-1.2.

transfer.

LM3460 Functional Diagram

Top View

See NS package Number MF05A

Ordering Information

Voltage

1.5

Order Number

Package Marking

Supplied As

LM3460M5-1.5

LM3460M5X-1.5

LM3460M5-1.2

LM3460M5X-1.5

D06A

D09A

1000 Unit Increments on Tape and Reel

3000 Unit Increments on Tape and Reel

1000 Unit Increments on Tape and Reel

3000 Unit Increments on Tape and Reel

1.5

1.2

MARKING CODE: The first letter ″D″ identifies the part as a Driver, and the next two numbers define the voltage for the part. The fourth letter indicates the

grade, with ″A″ designating the prime grade of product.

AVAILABILITY: The SOT23-5 package is only available in quantity of 1000 on tape and reel (designated by the letters ″M5″ in the part number), or in quantity

of 3000 on tape and reel (indicated by the letters ″M5X″ in the part number).

DS012603

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Typical Applications

DS012603-4

FIGURE 1. 1.5V Typical Application (See Application Information Section)

DS012603-5

FIGURE 2. 1.2V Typical Application (See Application Information Section)

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2

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Power Dissipation (T_A= 25˚C)

(Note 2)

300 mW

1500V

ESD Susceptibility (Note 3)

Human Body Model

See AN-450 ″Surface Mounting Methods and Their Effect

on Product Reliability″ for methods on soldering surface

mount devices.

Input Voltage V_IN

Output Current

20V

20 mA

150˚C

Junction Temperature

Storage Temperature

Operating Ratings (Note 1), (Note 2)

−65˚C to +150˚C

Lead Temperature

Vapor Phase (60 sec.)

Infared (15 sec.)

Ambient Temperature Range

Output Current

0˚C ≤ T_A≤ +70˚C

+215˚C

+220˚C

1 mA

Electrical Characteristics

LM3460-1.5

Specifications with standard type face are for T_J= 25˚C, and those with boldface type apply over full Operating Temperature

Range. Unless otherwise specified, (+)IN = V_REG, V_OUT= 200 mV

Symbol

V_REG

Parameter

Conditions

Typ (Note 4)

Limit (Note 5)

Units

Regulated Voltage

I_OUT= 1 mA

1.5

1.515/ 1.530

1.485/1.470

V (max)

V (min)

Regulated Voltage

Tolerance

±

2

1 /

% (max)

I_q

Quiescent Current

85

125/150

1/0.5

µA (max)

G_m

Transconductance

∆I_OUT/ ∆V_REG

20µA ≤ I_OUT≤ 1 mA

V_OUT= 500 mV

mA/mV

(min)

3.3

V_SAT

I_L

Output Saturation

Voltage(Note 6)

V_IN= V_REG+ 100 mV

I_OUT= 1 mA

0.8

0.1

0.95

V (max)

Output Leakage

Current

V_IN= V_REG− 100 mV

V_OUT= 0V

0.5/1.0

µA (max)

R_F

Internal Feedback

Resistor (See

Functional Diagram)

8.9

5.3

kΩ(max)

kΩ(min)

7.1

50

E_n

Output Noise Voltage

I_OUT= 1 mA, 10 Hz ≤ f ≤ 10kHz

µV (rms)

Electrical Characteristics

LM3460-1.2

Specifications with standard type face are for T_J= 25˚C, and those with boldface type apply over full Operating Temperature

Range. Unless otherwise specified, (+)IN = V_REG, V_OUT= 200 mV

Symbol

V_REG

Parameter

Conditions

Typ (Note 4)

Limit (Note 5)

Units

Regulated Voltage

I_OUT= 1 mA

1.220

1.232/ 1.244

1.208/1.196

V (max)

V (min)

Regulated Voltage

Tolerance

±

2

1 /

% (max)

I_q

Quiescent Current

85

125/150

1/0.5

µA (max)

G_m

Transconductance

∆I_OUT/ ∆V_REG

20µA ≤ I_OUT≤ 1 mA

V_OUT= 200 mV

mA/mV

(min)

3.3

V_SAT

I_L

Output Saturation

Voltage(Note 6)

V_IN= V_REG+ 100 mV

I_OUT= 1 mA

0.8

0.1

0.95

V (max)

Output Leakage

Current

V_IN= V_REG− 100 mV

V_OUT= 0V

0.5/1.0

µA (max)

R_F

Internal Feedback

Resistor (See

Functional Diagram)

12.5

7.5

kΩ(max)

kΩ(min)

10

50

E_n

Output Noise Voltage

I_OUT= 1 mA, 10 Hz ≤ f ≤ 10kHz

µV (rms)

3

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Electrical Characteristics

LM3460-1.2 ^(Continued)

Note 1: Absolute Maximum Ratings are 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. The guaran-

teed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test con-

ditions.

Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by T

(maximum junction temperature), θ (junction ot am-

JA

Jmax

bient thermal resistance), and T (ambient temperature). The maximum allowable power dissipation at any temperature is (P

= (T

− T )/θ ) or the number

Jmax A JA

A

Dmax

given in the Absolute Maximum Ratings, whichever is lower. The typical thermal resistance θ when soldered to a printed circuit board is approximately 330˚ C/W.

JA

Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.

Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control

(SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL).

Note 6: V

= V

− V

, when the voltage at the IN pin is forced 100mV above the nominal regulating voltage (V

).

REG

SAT

REG

OUT

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4

Product Description

The LM3460 is a shunt regulator designed for use as a pre-

cision control element in a feedback loop. The regulated out-

put voltage is sensed between the IN pin and GROUND pin

of the LM3460.

Applying a load pulse to the output of the regulator circuit

and observing the output voltage response is a good method

of verifying the stability of the control loop.

If excessive ringing on the output waveform is observed, this

usually indicates marginal stability resulting from insufficient

phase margin.

The output of the LM3460 sources current whenever the

voltage at the IN pin reaches the regulated voltage.

This current is used to cut off the drive to the external pass

trnasistor, which provides the negative feedback to force the

Test Circuit

output voltage to be the same value as V_REG

.

The test circuit shown in Figure 3 can be used to measure

various LM3460 parameters. Test conditions are set by forc-

ing the appropriate voltage at the V_OUTSet test point and se-

lecting the appropriate R_Lor I_OUTas specified in the Electri-

cal Characteristics section. Use a DVM at the ″measure″ test

points to read the data.

If the voltage on the IN pin is forced above the V_REGvoltage,

the maximum voltage applied to the IN pin should not ex-

ceed 20V. In addition, an external resistor may be required

on the OUT pin to limit the maximum current to 20 mA.

Compensation

The inverting input of the error amplifier is brought out to sim-

plify closed-loop compensation. Typically, compensation is

provided by a single capacitor connected from the COM-

PENSATION pin to the OUT pin of the LM3460.

DS012603-9

V_OUTSet Note: 0V to 500 mV for LM3460-1.5

0V to 200 mV for LM3460-1.2

FIGURE 3. Test Circuit

Setting the Output Voltage

If a regulated voltage is desired which is not available as a

standard voltage, the output voltage may be adjusted by us-

ing an external resistive divider (see Figure 4):

5

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PERFORMANCE DATA

Setting the Output Voltage (Continued)

All data taken at 20˚C ambient:

LOAD/LINE REGULATION: The output voltage changed

<

0.1 mV as the load was increased from 0-7A, and the input

voltage was varied from 3.0V-3.6V.

DROPOUT VOLTAGE: The dropout voltage (which is de-

fined as the minimum input-output voltage differential re-

quired to maintain a regulated output) was measured at 7A

and found to be 1.4V. This means that a minimum input volt-

age of 2.9V is required to keep the 1.5V output in regulation.

TRANSIENT RESPONSE: Transient response was tested

using a 0.2Ω power resistor connected to the output using a

mechanical contact to provide a 0-7A load current step.

When the load was applied, the change in output voltage

DS012603-10

<

was seen to be 5 mV with a total recovery time of about 30

µs (see Figure 5).

<

FOR BEST RESULTS: SELECT R_A500Ω

FIGURE 4. Setting the Output Voltage

The simplest way to calculate the resistor values is to as-

sume a value for R_Aand then solve the equation shown for

R_B.

To assure best output voltage accuracy, the value selected

DS012603-11

<

for R_Ashould be 500Ω, and 1% tolerance resistors should

FIGURE 5. Output Transient Response

be used.

As the ohmic value of R_Ais increased, the internal resistive

divider inside the LM3460 will cause the output voltage to

deviate from the value predicted by the formula shown.

HEATSINKING/COMPONENT SELECTION

HEATSINKING: As with any linear regulator, the power dissi-

pated in the pass transistor (Q4) is approximately:

App Circuit Technical Information

P = (V_IN− V_OUT) X I_LOAD

Figure 1 and Figure 2 highlight two applications of the

LM3460. This section provides details of circuit function.

Q4 must be provided with adequate heatsinking so that the

junction temperature never exceeds 150˚C.

Figure 6 shows the maximum allowable values of thermal

resistance (from heatsink-to-ambient) that must be provided

for various values of the load current.

1.5V/7A TYPICAL APPLICATION

Figure 1 shows the schematic of a wide-bandwidth linear

regulator which provides a regulated 1.5V output at up to 7A

of load current from a 3V-3.6V input.

The pass element of the regulator (which supplies the load

current) is made up of a three-transistor complimentary Dar-

lington composed of Q2, Q3, and Q4. The bias current flow-

ing through R1 will drive the pass element ON, until such

time as Q1 pulls down and takes the drive away from the

base of Q2.

The circuit regulates the output to 1.5V using the LM3460

precision controller, which sources current from its output

whenever the voltage at the IN pin reaches 1.5V.

When the LM3460 sources current from its output, it turns on

Q1 (stealing the base drive for Q2) which reduces the cur-

rent from the 1.5V regulated output. In this way, a negative

feedback loop is established which locks the output at 1.5V.

DS012603-12

C1 and C2 are used for compensation, and should be ce-

ramic capacitors.

FIGURE 6. Q4 Heatsink Requirements for Circuit

Shown in Figure 1

C4 is required for regulator stability, and both C3 and C4 af-

fect transient response. Circuit performance should be care-

fully evaluated if substitutions are made for these two com-

ponents.

These values are calculated assuming a maximum ambient

of 50˚C, 3.3V input, and a TO-220 power transistor mounted

using thermal grease and a mica insulator.

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6

Detailed information will be presented in the areas which dif-

fer between the two circuits.

App Circuit Technical Information

(Continued)

HEATSINKING

A given thermal resistance can be obtained by using differ-

ent combinations of heatsink and airflow (refer to heatsink

manufacturers datasheets).

The 1.2V design needs a little more heatsinking because the

lower output voltage means more power dissipation in Q4 at

any value of load current.

The design tradeoff here is that heatsinks which are smaller,

lighter, and cheaper require more airflow to get the desired

value of thermal resistance.

Figure 7 shows the maximum allowable values of thermal

resistance (from heatsink-to-ambient) that must be provided

for various values of the load current.

TRANSIENT RESPONSE: If the regulator is to respond

quickly to changes in load current demand, the input and

output capacitors must be selected carefully.

The output capacitor C4 is most critical, as it must supply

current to the load in the time it takes the regulator loop to

sense the output voltage change and turn on the pass tran-

sistor. A Sanyo Oscon type (or equivalent) will give the best

performance here.

The input capacitor C3 is also important, as it provides an

energy reservoir from which the regulator sources current to

force the output back up to the nominal value. A good, low

ESR electrolytic such as a Panasonic HFQ type is a good

choice for C3.

LAYOUT TIPS: In order to optimize performance, parasitic

inductance due to connecting traces must be minimized. All

paths shown as heavy lines on the schematic must be made

by traces which are wide and short as possible (component

placement should be optimized for minimum lead length).

DS012603-13

FIGURE 7. Q4 Heatsink Requirements for Circuit

shown in Figure 2

POWER TRANSISTOR AND DRIVER: The power transistor

used at Q4 must have very good current gain at 7A, and

wide bandwidth (high f_T) for this circuit to work as specified.

The D44H8 is an excellent choice for cost and performance.

Q1 DRIVE CIRCUITRY

In the circuit shown in Figure 1, the output of U1 drives the

base of Q1 with current when the voltage at V_OUTreaches

the regulation point. As Q1 turns ON, it steals drive from Q2

which holds the loop in regulation.

The current gain of Q4 dictates the power dissipation in its

driver (Q3) which must supply the base current to Q4. If the

gain of Q4 is lowered, Q3 must source more current into its

base (and the power dissipation in Q3 goes up proportion-

ately).

The circuit of Figure 2 uses a different drive configuration for

Q1, required because of the lower voltage across U1.

@

The D44H8 has a guaranteed minimum gain of 40 4A, with

With only 1.2V across U1, the OUT pin of the LM3460 can-

not swing up high enough in voltage to turn on the V_BEof Q1.

typical gain much higher. Assuming the gain of Q4 is about

30% lower at 7A, it will still be 28. Therefore, to support 7A

of load current, Q3 must supply 250 mA to the base of Q4

(worst case).

>

In the circuit of Figure 2, drive for Q1 is provided by R7, but

only when U1 sources current: The operation of the drive

scheme is as follows:

The power dissipation in Q3 (assuming 3.3V input) will never

exceed approximately 250 mW, which is easily handled by

2N3906 in a TO-92 case (which has a thermal resistance of

about 180˚C/W), but could be a problem for a very small sur-

face mount device.

If the voltage at V_OUTis below 1.2V, no current flows from

the OUT pin of U1. Q1 is held OFF as the current flowing

down through R7 goes through D1 and R5 to ground.

IMPORTANT: Diode D1 is a 1N4001 because its V_Fmust be

much less than the V_BEof Q1 (a signal diode like 1N4148 will

not work here).

If substitutions are made for Q3 or Q4, careful attention must

be paid to the current gain as well as the f_T.

When U1 is not sourcing current, the voltage at the OUT pin

(and the cathode of D1) will be held at about 50 mV by the

R7/D1/R5 divider. The current flowing to ground through

these components is about 110 µA.

TRANSISTOR BANDWIDTH: Fast transient response that

the regulator be able to respond quickly to any change in

output voltage (which will occur if the current drawn by the

load suddenly changes).

Because D1 is a 1A power diode, the V_Facross D1 at this

small value of current will be much less than the V_BEneeded

to turn ON Q1 (so Q1 is held off by D1).

All of the transistors specified in the schematic are very

wide-band devices (have high f_Tvalues) which is necessary

for fast response. If substitutions are made for any of the

transistors, this specification must be considered.

When U1 begins to source current (to cut off the pass tran-

sistor and regulate V_OUT) it forces the voltage at the cathode

of D1 to rise.

1.2V/7A TYPICAL APPLICATION

This action causes the current that was flowing through D1

to flow into the base of Q1, turning it ON and taking drive

away from the base of Q2.

@

The 1.2V 7A design in Figure 2 is very similar in function

to the design shown in Figure 1. Most of the circuit descrip-

tions previously detailed for that circuit apply unchanged to

Figure 2, will not be repeated.

This action provides the negative feedback required to regu-

late V_OUTand allows the LM3460 to operate with only 1.2V

of total supply voltage across the device.

7

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Physical Dimensions inches (millimeters) unless otherwise noted

5-Lead Small Outline Package (M5)

Order Number, See Ordering Information Table

NS Package Number MF05A

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

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.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

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Tel: 1-800-272-9959

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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.

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Products > Analog - Regulators > Regulator Control & Supervisory Function > LM3460

LM3460 Product Folder

Precision Controller for GTLp and GTL Bus Termination

Generic P/N 3460

General

Description

Package

& Models

Samples

& Pricing

Features

Datasheet

Parametric Table

Multiple Output Capability

On/Off Pin

Parametric Table

No

-

Output Current, max

Output Voltage (Volt)

Adjustable Output

15 mA

1.20, 1.50

Error Flag

-

Input Voltage, min (Volt)

Input Voltage, max (Volt)

Switching Frquency (Hz)

Adjustable Switching

Sync Pin

-

20

-

No

Datasheet

Size in

Kbytes

Title

Date

Receive via

Email

Download

View Online

28-

Jul-

00

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LM3460-1.2, -1.5 Precision Controller for GTLp and GTL 166

View Online Download

Bus Termination

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LM3460-1.2, -1.5 Precision Controller for GTLp and GTL

Bus Termination (JAPANESE)

99

Kbytes

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Package Availability, Models, Samples & Pricing

Samples &

Budgetary Pricing

Std

Pack

Size

Package

Models

Package

Marking

Part Number

Status

Electronic

Orders

Type Pins MSL

SPICE IBIS

Qty

$US each

Samples

reel

of

1000

D09A

¢Z¢1¢T

SOT-23

MSL

LM3460M5-1.2

5

Full production N/A

N/A

1K+

$0.8300

Buy Now

Samples

reel

of

1000

D06A

¢Z¢1¢T

LM3460M5-1.5

1K+

$0.8300

Buy Now

reel

of

3000

D09A

¢Z¢1¢T

SOT-23

MSL

LM3460M5X-1.2

LM3460M5X-1.5

LM3460-1.2 MDC

LM3460-1.5 MDC

LM3460-1.2 MWC

LM3460-1.5 MWC

5

Full production N/A

N/A

1K+

$0.8300

Buy Now

reel

of

3000

D06A

¢Z¢1¢T

tray

of

N/A

Samples

Die

-

tray

of

N/A

Die

wafer jar

of

Wafer

N/A

wafer jar

of

N/A

General Description

The LM3460 is a monolithic integrated circuit designed for precision control of GTLplus and GTL Bus

termination. This controller is available in a tiny SOT23-5 package, and includes an internally compensated

op amp, a bandgap reference, an NPN output transistor, and voltage setting resistors.

A trimmed precision bandgap voltage reference utilizes temperature drift curvature correction for excellent

voltage stability over the operating range. The precision output control enables the termination voltage to

maintain tight regulation, despite fast switching requirements on the bus.

The LM3460 controller is designed to be used with a high current (> 7A) NPN pass transistor to provide the

high current needed for the bus termination. The wide bandwidth of the feedback loop provides excellent

transient response, and greatly reduces the output capacitance required, thus reducing cost and board space

requirements.

Features

●

Precision output (1%)

Output voltage can be adjusted

Extremely fast transient response in GTLp and GTL bus termination

Tiny SOT23-5 package

Output voltage capability for GTL or GTLp

Low temperature coefficient

Applications

●

GTL bus termination (1.2V output @ 7A)

GTLp bus termination (1.5V output @ 7A)

Adjustable high-current linear regulator

[Information as of 5-Aug-2002]

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型号：	LM3460-1.2MDC
厂家：	National Semiconductor
描述：	IC 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 1.22 V, UUC, DIE, Voltage Reference 输出元件
文件：	总12页 (文件大小：234K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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