US431ALCL [UNISEM]

LOW -VOLTAGE ADJUSTABLE PRECISION SHUNT REGULATOR; 低 - 电压可调精密并联稳压器


型号：	US431ALCL
厂家：	UNISEM
描述：	LOW -VOLTAGE ADJUSTABLE PRECISION SHUNT REGULATOR 低 - 电压可调精密并联稳压器稳压器
文件：	总6页 (文件大小：41K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

US431L/431AL

LOW -VOLTAGE ADJUSTABLE

PRECISION SHUNT REGULATOR

PRELIMINARY DATASHEET

FEATURES

DESCRIPTION

SOT23-5 package

The US431L product is a 3 terminal adjustable shunt

regulator that can also be used as a precision voltage

reference. Its output voltage may be set to any value

between Vref(1.24V) and 6V with two external resistors

as shown in the typical application circuit. Other appli-

cations of this device include the use as a merged am-

plifier and reference in applications such as Linear regu-

lator or as the secondary side controller in low voltage

power supply applications. The US431L only requires

80uA maximum quiescent current before regulating,

making it ideal as a voltage reference for battery type

applications.

0.5% Voltage Reference Initial Accuracy

(US431AL)

Low Operational Cathode Current

(80 uA max)

Unconditionally Stable with only 1uF

Adjustable Output from 1.24V to 6V

0.25W Typical Output Impedance

Pin to Pin Compatible with TLV431

APPLICATIONS

Precision Voltage Reference

Linear Regulator Controller

Secondary Side Controller for the Low Voltage

Power Supply Applications

TYPICAL APPLICATION

US431

431app1-1.0

Vo = Vref ´ 1+

Typical application of the US431L as a shunt regulator / voltage reference.

PACKAGE ORDER INFORMATION

Ta (°C)

5 LEAD

SOT23-5

3 PIN PLASTIC

TO-92

8 PIN PLASTIC

SOIC

0 TO 70

US431LCL

US431ALCL

US431LCZ

US431ALCZ

US431LCS

US431ALCS

Rev. 1.2

5/11/98

2-1

US431L/431AL

ABSOLUTE MAXIMUM RATINGS

Input Voltage (Vin) .............................................................

Continuous Cathode Current Range ......................................... -20 mA to +20 mA

Reference Current Range ...................................................... -0.05 mA to 3 mA

Storage Temperature Range ................................ -65°C TO 150°C

Operating Junction Temperature Range ...................... 0°C TO 150°C

PACKAGE INFORMATION

5 PIN SOT 23 (L)

3 PIN PLASTIC TO-92 (Z)

8 PIN PLASTIC SOIC (S)

TOP VIEW

BOTTOM VIEW

TOP VIEW

Cathode

Ref

Anode

Ref

Anode

Cathode

Anode

Cathode

Ref

qJA = 450°C/W

qJA = 162°C/W

qJA=160°C/W

ELECTRICAL SPECIFICATIONS

Unless otherwise specified ,these specifications apply over Ta=0 to 70 °C, CO =1uF. Typical values refer to

Ta=25 °C.Low duty cycle pulse testing are used which keeps junction and case temperatures equal to the

ambient temperature.

PARAMETER

Reference Voltage

US431L

Reference Voltage

US431AL

SYM

Vref

TEST CONDITION

IK=10mA,VKA=Vref,Ta=25°C

IK=10mA,VKA=Vref

IK=10mA,VKA=Vref,Ta=25°C

IK=10mA,VKA=Vref

VKA=Vref, IK=10mA

Note 1

MIN

TYP MAX

UNITS

1.228 1.240 1.252

1.221 1.240 1.259

1.234 1.240 1.246

1.228 1.240 1.252

Vref

Vref deviation over full

temperature range

Vref(dev)

Ratio of Vref change to dVref/dVKA IK=10mA , dVKA=Vref to 6 V

Cathode voltage change

-1.5

-2.7

mV/V

Reference pin current

Iref deviation over full

temperature range

IK=10mA , R1=10kW , R2=open

Note 1

0.15

0.05

0.5

0.3

Iref(dev)

Minimum cathode current IK(min)

VKA=Vref

VKA=6V , Vref=0V

VKA=Vref, f<1 kHz,

IK=0.1 to 15 mA , Note 2

0.001

0.25

0.1

0.4

Off state cathode current

Dynamic impedance

Ioff

Zka0

Note 1 : The deviation parameters, Vref(dev) and Iref(dev) are

defined as the differences between the maximum and the minimum

values obtained over the rated temperature range. The average full

range temperature coeficient of the reference input voltage is de-

fined as :

Note 2 :

Thedynamic impedance when VKA = Vref is defined as :

DVKA

Zka0 =

DIK

When the device is operating with two external

resistors (see Figure 2), the total dynamic impedance

of the circuit is given by:

Vref(dev)

Vref(25°C)

DTA

´ 10⁶

a Vref =

Where:

Zka =

= Zka0 ´ 1+

a Vref unit is ppm/°C

DTA is the rated operating free air temperature

of the device.

a Vref can be positive or negative depending on whether

minimum Vref or maximum Vref, respectively occurs at the

lower temperature.

Rev. 1.2

5/11/98

2-2

US431L/431AL

Pin Descr ipt ions

SOT 23

TO 92

8 PIN

SOIC

PIN#

Pin Description

PIN#

PIN SYMBOL

A resistor divider from this pin to the Cathode pin and

ground sets the output voltage.

Ref

The output of the shunt regulator .A minimum of 1uF

capacitor must be connected from this pin to Anode pin

to insure unconditional stability.

Ground pin. This pin must be connected to the lowest

potential in the system & all other pins must be at higher

potential with respect to this pin.

Cathode

Anode

3,6

These pins are not connected internally.

1,2

2,4,5,7

BLOCK DIAGRAM

Cathode

Ref

1.24V

431blk1-1.0

Anode

Figure 1 - Simplified block diagram of the US431L

Rev. 1.2

5/11/98

2-3

US431L/431AL

The maximum value for the biasing resistor is calcu-

lated using the following equations :

APPLICATION INFORMATION

VMIN - VKA

Output Voltage Setting

RBMAX

IB MAX + ILMAX

The US431L can be programmed to any voltages in the

range of 1.24 to 6V with the addition of R1 and R2 exter-

nal resistors according to the following formula:

IBMAX = IKMIN + IR

Where :

VMIN = Minimum supply voltage

I_LMAX= Maximum load current

IBMAX = Maximum bias current

I_KMIN = Maximum value for the minimum

cathode current spec

Vo = VKA = Vref ´ 1+

+ Iref ´ R1

The US431L keeps a constant voltage of 1.240V be-

tween the Ref pin and ground pin. By placing a resistor

R2 across these two pins a constant current flows

through R2, adding to the Iref current and into the R1

resistor producing a voltage equal to the (1.240/R2)*R1

+ Iref * R1 which will be added to the 1.240V to set the

output voltage as shown in the above equation. Since

the Input bias current of the Ref pin is 0.5 uA max , it

adds a very small error to the output voltage and for most

applications can be ignored . For example, in a typical

5V to 3.3V application where R2=1.21kW and R1=2kW

the error due to the Iadj is only 1mV which is about

0.03% of the nominal set point.

IR = Current through R1

Assuming R1=2kW as before,

3.3 - 1.24

I^R=

= 1.03 mA

IBMAX = 0.08 +1.03 = 1.11 mA

4.5 - 3.3

RB MAX

= 108 W

1.11+10

Selecting RB = 100 W

The maximum power dissipation of the resistor is

calculated under the maximum supply voltage as

follows :

V^MAX- VKA

(

)

P_{R (MAX)}

VIN

VKA = VO

Where :

US431

VMAX = Maximum supply voltage

PR^B(MAX) = Maximum RB power dissipation

431app2-1.0

6 - 3.3

(

)

PRB(MAX) =

= 73 mW

100

Thermal Design

Figure 2 - Typical application of the US431L for program-

ming the output voltage.

The US431L is offered in the plastic TO-92 (Z) or the

surface mount SOT23-5 (L) packages. The TO-92 pack-

age has the maximum power dissipation capability of

775mW at Ta=25°C with the derating factor of -6.2mW/

°C.The SOT23-5 package has the maximum power dis-

sipation capability of 150mW at Ta =25°C with the

derating factor of -1.2mW/°C.

Table below summarizes the maximum power dissipa-

tion capability of each package versus ambient tempera-

ture.

Biasing Resistor (RB) Selection

The biasing resistor RB is selected such that it does

not limit the input current under the minimum input

supply and maximum load and biasing current.

An example is given below on how to properly select

the biasing resistor.

Assuming :

VMIN = 4.5 V

VMAX = 6 V

VKA = 3.3 V

IL = 10 mA

Ambient Temperature (Ta) -°C

Pkg

TO 92 775mW 682mW 620mW 558mW 496mW

SOT23-5 150mW 132mW 120mW 108mW 96mW

Rev. 1.2

5/11/98

2-4

US431L/431AL

In our previous example, the maximum power dissipa-

tion of the device is calculated under no load and maxi-

mum input supply condition.

The maximum power is calculated using the following

equation :

V^MAX- VKA

P^MAX= V^KA´

Where :

P^MAX

Maximum power dissipation of the 431L

For our example :

6 - 3.3

P^MAX= 3.3 ´

= 89 mW

100

As shown in the power dissipation table, both packages

can handle this power dissipation.

Stability

The US431L has many different regions of stability do-

main as a function of the cathode current which are typi-

cal characteristics of the 3 terminal shunt regulators.

However in general the device will be unconditionaly

stable for any cathode current if the capacitor, CO =

1 uF or bigger is connected from Cathode to Anode

pins. If the cathode current is always kept higher than

500uA under minimum line and maximum load condi-

tions , the CO can be cut to 0.01uF and the system will

be stable.

Rev. 1.2

5/11/98

2-5

US431L/431AL

TYPICAL APPLICATION

I740 Application

VIN

VOUT

12V

431app3-1.1

Figure 3- Low cost 3.3V to 2.7V 0utput for Intel I740 application.

Ref Desig

C1,2

Description

Shunt Regulator

Capacitor

Resistor

Qty Part #

Manuf

Unisem

US431L

Elect,220uF,6.3V,ECAOJFQ221 Panasonic

6.2kW, 5%, SMT

118W, 1%, SMT

100W, 1% SMT

HS1

Heat Sink

Use minimum of 1" Square Copper Pad area

for load current <4A

Rev. 1.2

5/11/98

2-6

US431ALCL [UNISEM]

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