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參數(shù)資料

型號：	LM3420
廠商：	National Semiconductor Corporation
英文描述：	Lithium-Ion Battery Charge Controller
中文描述：	鋰離子電池充電控制器
文件頁數(shù)：	10/17頁
文件大?。?/td>	384K
代理商：	LM3420

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Five Lead Surface Mount Package Information

The small SOT23-5 package allows only 4 alphanumeric characters to identify the product. The table below contains the field in-

formation marked on the package.

The first letter “D” identifies the part as a Driver, the next two numbers indicate the voltage, “02” for a 4.2V part, “07” for an 8.2V

part, “03” for an 8.4V part, “04” for a 12.6V part, and “05” for a 16.8V part. The fourth letter indicates the grade, “B” for standard

grade, “A” for the prime grade.

The SOT23-5 surface mount package is only available on tape in quantity increments of 1000 on tape and reel (indicated by the

letters “M5” in the part number), or in quantity increments of 3000 on tape and reel (indicated by the letters “M5X” in the part num-

ber).

Product Description

The LM3420 is a shunt regulator specifically designed to be

the reference and control section in an overall feedback loop

of a Lithium-Ion battery charger. The regulated output volt-

age is sensed between the IN pin and GROUND pin of the

LM3420. If the voltage at the IN pin is less than the LM3420

regulating voltage (V

), the OUT pin sources no current.

As the voltage at the IN pin approaches the V

voltage,

the OUT pin begins sourcing current. This current is then

used to drive a feedback device (opto-coupler), or a power

device (linear regulator, switching regulator, etc.), which ser-

vos the output voltage to be the same value as V

REG

In some applications, (even under normal operating condi-

tions) the voltage on the IN pin can be forced above the

voltage. In these instances, the maximum voltage ap-

plied to the IN pin should not exceed 20V. In addition, an ex-

ternal 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 al-

low overall closed-loop compensation. In many of the appli-

cations circuits shown here, compensation is provided by a

single capacitor (C

) connected from the compensation pin

to the out pin of the LM3420. The capacitor values shown in

the schematics are adequate under most conditions, but

they can be increased or decreased depending on the de-

sired loop response. Applying a load pulse to the output of a

regulator circuit and observing the resultant output voltage

response is an easy method of determining the stability of

the control loop.

Analyzing more complex feedback loops requires additional

information.

The formula for AC gain at a frequency (f) is as follows;

where R

≈

75 k

for the 4.2V part, R

≈

181 k

for the 8.4V

part, R

≈

287 k

for the 12.6V part, and R

≈

392 k

for the

16.8V part.

The resistor (R

) in the formula is an internal resistor located

on the die. Since this resistor value will affect the phase mar-

gin, the worst case maximum and minimum values are im-

Voltage

Grade

Order

Package

Marking

D02A

D02B

D07A

D07B

D03A

D03B

D04A

D04B

D05A

D05B

Supplied as

Information

LM3420AM5-4.2

LM3420AM5X-4.2

LM3420M5-4.2

LM3420M5X-4.2

LM3420AM5-8.2

LM3420AM5X-8.2

LM3420M5-8.2

LM3420M5X-8.2

LM3420AM5-8.4

LM3420AM5X-8.4

LM3420M5-8.4

LM3420M5X-8.4

LM3420AM5-12.6

LM3420AM5X-12.6

LM3420M5-12.6

LM3420M5X-12.6

LM3420AM5-16.8

LM3420AM5X-16.8

LM3420M5-16.8

LM3420M5X-16.8

4.2V

8.2V

8.4V

12.6V

16.8V

A (Prime)

B (Standard)

A (Prime)

B (Standard)

A (Prime)

B (Standard)

A (Prime)

B (Standard)

A (Prime)

B (Standard)

1000 unit increments on tape and reel