LM3460M5X-1.5/NOPB [TI]

1-OUTPUT THREE TERM VOLTAGE REFERENCE, 1.5V, PDSO5, SOT-23, 5 PIN;


型号：	LM3460M5X-1.5/NOPB
厂家：	TEXAS INSTRUMENTS
描述：	1-OUTPUT THREE TERM VOLTAGE REFERENCE, 1.5V, PDSO5, SOT-23, 5 PIN 光电二极管输出元件
文件：	总9页 (文件大小：580K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

March 2005

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 sta-

bility over the operating range. The precision output control

enables 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)

The LM3460 controller is designed to be used with a high

n GTLp bus termination (1.5V output 7A)

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

n Adjustable high-current linear regulator

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.

5-Lead Outline Package (M5)

Actual Size

Connection Diagram and Package

Information

01260302

01260303

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

transfer.

01260301

*This resistor is not used on the LM3460-1.2.

Top View

LM3460 Functional Diagram

See NS package Number MF05A

Ordering Information

Voltage

Order Number

LM3460M5-1.5

LM3460M5X-1.5

LM3460M5-1.2

LM3460M5X-1.5

Package Marking

Supplied As

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

01260304

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

01260305

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

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Absolute Maximum Ratings (Note 1)

ESD Susceptibility (Note 3)

Human Body Model

1500V

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

See AN-450 "Surface Mounting Methods and Their Effect

on Product Reliability" for methods on soldering surface

mount devices.

Input Voltage V_IN

20V

20 mA

Output Current

Junction Temperature

Storage Temperature

Lead Temperature

Vapor Phase (60 sec.)

Infared (15 sec.)

150˚C

Operating Ratings (Note 1), (Note 2)

−65˚C to +150˚C

Ambient Temperature Range

0˚C ≤ T_A≤ +70˚C

Output Current

1 mA

+215˚C

+220˚C

Power Dissipation (T_A= 25˚C)

(Note 2)

300 mW

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 Tempera-

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

Symbol

V_REG

Parameter

Conditions

Typ (Note 4)

Limit (Note 5)

1.515/ 1.530

1.485/1.470

Units

V (max)

V (min)

Regulated Voltage

I_OUT= 1 mA

1.5

Regulated Voltage

Tolerance

1 /

% (max)

I_q

Quiescent Current

Transconductance

∆I_OUT/ ∆V_REG

125/150

1/0.5

µA (max)

mA/mV

(min)

G_m

20µA ≤ I_OUT≤ 1 mA

V_OUT= 500 mV

V_IN= V_REG+ 100 mV

I_OUT= 1 mA

3.3

V_SAT

I_L

Output Saturation

Voltage(Note 6)

Output Leakage

Current

0.8

0.1

0.95

V (max)

V_IN= V_REG− 100 mV

V_OUT= 0V

0.5/1.0

µA (max)

R_F

Internal Feedback

Resistor (See

8.9

5.3

kΩ(max)

kΩ(min)

7.1

Functional Diagram)

Output Noise Voltage

E_n

I_OUT= 1 mA, 10 Hz ≤ f ≤ 10kHz

µV (rms)

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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 Tempera-

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

Symbol

V_REG

Parameter

Conditions

Typ (Note 4)

Limit (Note 5)

1.232/ 1.244

1.208/1.196

Units

V (max)

V (min)

Regulated Voltage

I_OUT= 1 mA

1.220

Regulated Voltage

Tolerance

1 /

% (max)

I_q

Quiescent Current

Transconductance

∆I_OUT/ ∆V_REG

125/150

1/0.5

µA (max)

mA/mV

(min)

G_m

20µA ≤ I_OUT≤ 1 mA

V_OUT= 200 mV

V_IN= V_REG+ 100 mV

I_OUT= 1 mA

3.3

V_SAT

I_L

Output Saturation

Voltage(Note 6)

Output Leakage

Current

0.8

0.1

0.95

V (max)

V_IN= V_REG− 100 mV

V_OUT= 0V

0.5/1.0

µA (max)

R_F

Internal Feedback

Resistor (See

12.5

7.5

kΩ(max)

kΩ(min)

Functional Diagram)

Output Noise Voltage

E_n

I_OUT= 1 mA, 10 Hz ≤ f ≤ 10kHz

µV (rms)

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

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

test conditions.

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

(maximum junction temperature), θ (junction ot

Jmax

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

= (T

− T )/θ ) or the

Dmax

Jmax A JA

number 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.

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

OUT

REG

SAT

REG

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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.

Product Description

The LM3460 is a shunt regulator designed for use as a

precision control element in a feedback loop. The regulated

output voltage is sensed between the IN pin and GROUND

pin of the LM3460.

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.

Test Circuit

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

trnasistor, which provides the negative feedback to force the

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

selecting the appropriate R_Lor I_OUTas specified in the

Electrical Characteristics section. Use a DVM at the "mea-

sure" 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

simplify closed-loop compensation. Typically, compensation

is provided by a single capacitor connected from the COM-

PENSATION pin to the OUT pin of the LM3460.

01260309

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

0V to 200 mV for LM3460-1.2

FIGURE 3. Test Circuit

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

affect transient response. Circuit performance should be

carefully evaluated if substitutions are made for these two

components.

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

using an external resistive divider (see Figure 4):

PERFORMANCE DATA

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

voltage of 2.9V is required to keep the 1.5V output in regu-

lation.

01260310

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

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

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

be used.

01260311

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.

FIGURE 5. Output Transient Response

App Circuit Technical Information

HEATSINKING/COMPONENT SELECTION

Figure 1 and Figure 2 highlight two applications of the

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

sipated in the pass transistor (Q4) is approximately:

LM3460. This section provides details of circuit function.

P = (V_IN− V_OUT) X I_LOAD

1.5V/7A TYPICAL APPLICATION

Q4 must be provided with adequate heatsinking so that the

junction temperature never exceeds 150˚C.

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.

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.

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

flowing 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.

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

ramic capacitors.

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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

surface mount device.

App Circuit Technical Information

(Continued)

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

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

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).

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.

1.2V/7A TYPICAL APPLICATION

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.

01260312

FIGURE 6. Q4 Heatsink Requirements for Circuit

Detailed information will be presented in the areas which

differ between the two circuits.

Shown in Figure 1

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.

HEATSINKING

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.

A given thermal resistance can be obtained by using differ-

ent combinations of heatsink and airflow (refer to heatsink

manufacturers datasheets).

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.

The design tradeoff here is that heatsinks which are smaller,

lighter, and cheaper require more airflow to get the desired

value of thermal resistance.

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

transistor. 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).

01260313

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.

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

cannot swing up high enough in voltage to turn on the V_BEof

Q1.

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

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).

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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).

App Circuit Technical Information

(Continued)

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:

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

transistor and regulate V_OUT) it forces the voltage at the

cathode of D1 to rise.

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.

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.

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).

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.

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.

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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

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.

For the most current product information visit us at www.national.com.

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(b) support or sustain life, and whose failure to perform when

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device or system whose failure to perform can be reasonably

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LM3460M5X-1.5/NOPB [TI]

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