US1150CM [UNISEM]

4A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR; 4A超低压差正可调稳压


型号：	US1150CM
厂家：	UNISEM
描述：	4A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR 4A超低压差正可调稳压
文件：	总5页 (文件大小：38K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

US1150

4A ULTRA LOW DROPOUT POSITIVE

ADJUSTABLE REGULATOR

PRELIMINARY DATASHEET

DESCRIPTION

FEATURES

The US1150 product is a 4A regulator with extremely

low dropout voltage using a proprietary Bipolar pro-

cess that achieves comparable equivalent on re-

sistance to that of discrete MOSFETs. This product is

specifically designed to provide well regulated supply for

applications requiring 2.8V or lower voltages from

3.3V ATX power supplies where high efficiency of

a switcher can be achieved without the cost and

complexity associated with switching regulators.

One such application is the new graphic chip sets that

require anywhere from 2.4V to 2.7V supply such as the

Intel I740 chip set.

0.7V Dropout at 4A

Fast Transient Response

1% Voltage Reference Initial Accuracy

Built-in Thermal Shutdown

APPLICATIONS

3.3V to 2.7V Intel I740 chip set.

TYPICAL APPLICATION

3.3V

Vin

Vctrl

Vout

2.7V

US1150

Adj

Vsense

1150app1-1.0

Typical application of US1150 in a 3.3V to 2.7V for I740 chip.

PACKAGE ORDER INFORMATION

Tj (°C)

5 PIN PLASTIC

TO263 (M)

US1150CM

5 PIN PLASTIC

POWER FLEX (P)

US1150CP

8 PIN PLASTIC

SOIC (S)

US1150CS

0 TO 125

Rev. 1.2

10/28/99

2-1

US1150

ABSOLUTE MAXIMUM RATINGS

Input Voltage (Vin) ........................................................... 7V

Control Input Voltage (Vctrl) .................................................. 14V

Power Dissipation............................................. Internally Limited

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

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

PACKAGE INFORMATION

8 PIN PLASTIC SOIC ( S )

5 PIN PLASTIC TO263 ( M )

5 PIN PLASTIC POWER FLEX (P)

FRONT VIEW

TOP VIEW

Vin

Vctrl

Vin

Vout

Vctrl

Vout

Adj

Vsense

qJA=55°C/W for 1" Sq pad area

qJA=35°C/W for 0.5" square pad

ELECTRICAL SPECIFICATIONS

Unless otherwise specified ,these specifications apply over ,Cin=1uF,Cout=10uF, and Tj=0 to 125°C.Typical

values refer to Tj=25°C. Vout=Vsense.

PARAMETER

Reference Voltage

SYM TEST CONDITION

Vref Vctrl=2.75V,Vin=2V,Io=10mA

Tj=25,Vadj=0V

MIN

TYP

MAX UNITS

1.243 1.250 1.257

Vctrl=2.7to12V,Vin=2.05V to 5.5V, 1.237 1.250 1.263

Io=10mA to 4A,Vadj=0V

Line Regulation

Vctrl=2.5Vto7V,Vin=1.75Vto5.5V

,Io=10mA ,Vadj=0V

Vctrl=2.75V,Vin=2.1V,Io=10mA

to 4A,Vadj=0V

Vadj=0V for all conditions below.

Vin=2.05V,Io=1.5A

Vin=2.05V,Io=3A

Load Regulation (note 1)

Dropout Voltage (note 2)

(Vctrl - Vout)

1.15

1.18

1.25

Vin=2.05V,Io=4A

1.10

Dropout Voltage (note 2)

(Vin - Vout)

Vadj=0V for all conditions below.

Vctrl=2.75V,Io=1.5A

Vctrl=2.75V,Io=3A

0.26

0.50

0.70

0.38

0.60

0.85

Vctrl=2.75V,Io=4A

Current Limit

Vctrl=2.75V,Vin=2.05V,

dVo=100mV Vadj=0V

4.2

Minimum Load Current (note 3)

Thermal Regulation

Ripple Rejection

Vctrl=5V,Vin=3.3V,Vadj=0V,

30 mS Pulse

Vctrl=5V,Vin=5V,Io=4A,Vadj=0V

Tj=25,Vripple=1Vpp at 120Hz

0.01

0.02

%/W

Rev. 1.2

10/28/99

2-2

US1150

ELECTRICAL SPECIFICATIONS

PARAMETER

Control Pin Current

SYM TEST CONDITION

MIN TYP MAX UNITS

Vadj=0V for all below conditions.

Vctrl=2.75V,Vin=2.05V,Io=1.5A

Vctrl=2.75V,Vin=2.05V,Io=3A

Vctrl=2.75V,Vin=2.05V,Io=4A

Adjust Pin Current

Iadj

Vctrl=2.75V,Vin=2.05V,Vadj=0V,

120

Note 1 : Low duty cycle pulse testing with Kelvin con-

nections are required in order to maintain accurate data.

Note 2 : Drop-out voltage is defined as the minimum

differential between Vin and Vout required to maintain

regulation at Vout. It is measured when the output volt-

age drops 1% below its nominal value.

Note 3 : Minimum load current is defined as the mini-

mum current required at the output in order for the out-

put voltage to maintain regulation. Typically the resistor

dividers are selected such that it automatically main-

tains this current.

PIN DESCRIPTIONS

PIN # PIN SYMBOL PIN DESCRIPTION

Vsense

This pin is the positive side of the reference which allows remote load sensing

to achieve excellent load regulation.

Adj

Vout

A resistor divider from this pin to the Vout pin and ground sets the output voltage.

The output of the regulator. A minimum of 10uF capacitor must be connected from this

pin to ground to insure stability.

Vctrl

Vin

This pin is the supply pin for the internal control circuitry as well as the base drive for

the pass transistor.This pin must always be higher than the Vout pin in order for

the device to regulate.(see specifications)

The input pin of the regulator.Typically a large storage capacitor is connected from this

pin to ground to insure that the input voltage does not sag below the minimum drop

out voltage during the load transient response.This pin must always be higher than

Vout in order for the device to regulate.(see specifications)

Rev. 1.2

10/28/99

2-3

US1150

BLOCK DIAGRAM

Vin

Vout

Vctrl

Vsense

1.25V

CURRENT

LIMIT

THERMAL

SHUTDOWN

Adj

1150blk1-1.1

Figure 1 - Simplified block diagram of the US1150

The US1150 is specifically designed to meet the fast

current transient needs as well as providing an accurate

initial voltage , reducing the overall system cost with the

need for fewer number of output capacitors.Another fea-

ture of the device is its true remote sensing capability

which allows accurate voltage setting at the load rather

than at the device.

APPLICATION INFORMATION

Introduction

The US1150 adjustable regulator is a 5 terminal device

designed specificaly to provide extremely low dropout

voltages comparable to the PNP type without the disad-

vantage of the extra power dissipation due to the base

current associated with PNP regulators.This is done by

bringinging out the control pin of the regulator that pro-

vides the base current to the power NPN and connect-

ing it to a voltage that is grater than the voltage present

at the Vin pin.This flexebility makes the US1150 ideal

for applications where dual inputs are available such as

a computer motherboard with an ATX style power sup-

ply that provides 5V and 3.3V to the board.One such

application is the new graphic chip sets that require any-

where from 2.4V to 2.7V supply such as the Intel I740

chip set. The US1150 can easily be programmed with

the addition of two external resistors to any voltages

within the range of 1.25 to 5.5 V. Another major require-

ment of these graphic chips such as the Intel I740 is the

need to switch the load current from zero to several amps

in tens of nanoseconds at the processor pins ,which

translates to an approximately 300 to 500 nS of current

step at the regulator . In addition, the output voltage tol-

erances are also extremely tight and they include the

transient response as part of the specification.

Output Voltage Setting

The US1150 can be programmed to any voltages in the

range of 1.25V to 5.5V with the addition of R1 and R2

external resistors according to the following formula:

R²

_R1ø

V^OUT= V^REF1+

+ I^ADJ´ R²

Wehre : V^REF=1.25V Typically

I^ADJ=50 uA Typically

R¹& R2 as shown in figure 2

Vin

Vout

Vin

Vout

US1150

Adj

Vctrl

Vsense

Vctrl

Vref

IAdj = 50uA

1150app2-1.1

Figure 2 - Typical application of the US1150 for

programming the output voltage.

Rev. 1.2

10/28/99

2-4

US1150

The US1150 keeps a constant 1.25V between the Vsense

pin and the Vadj pin. By placing a resistor R1 across

these two pins and connecting the Vsense and Vout pin

together , a constant current flows through R1, adding

to the Iadj current and into the R2 resistor producing a

voltage equal to the (1.25/R1)*R2 + Iadj*R2 .This voltage

is then added to the 1.25V to set the output voltage.

This is summarized in the above equation. Since the

minimum load current requirement of the US1150 is 10

mA , R1 is typically selected to be a 121W resistor so

that it automatically satisfies this condition. Notice that

since the Iadj is typically in the range of 50uA it only

adds a small error to the output voltage and should be

considered when very precise output voltage setting is

required.

For most applications a minimum of 100uF aluminum

electrolytic capacitor such as Sanyo, MVGX series

,Panasonic FA series as well as the Nichicon PL series

insures both stability and good transient response.

Thermal Design

The US1150 incorporates an internal thermal shutdown

that protects the device when the junction temperature

exceeds the allowable maximum junction temperature.

Although this device can operate with junction tempera-

tures in the range of 150°C ,it is recommended that the

selected heat sink be chosen such that during maxi-

mum continuos load operation the junction temperature

is kept below this number. The example below shows

the steps in selecting the proper surface mount pack-

age.

Load Regulation

Assuming, the following conditions:

Vout=2.7V

Vin=3.3V

Vctrl=5V

Iout=2A DC Avg

Calculate the maximum power dissipation using the fol-

lowing equation:

Pd=Iout*(Vin-Vout) + (Iout/60)*(Vctrl - Vout)

Pd=2*(3.3-2.7) + (2/60)*(5-2.7)=1.28 W

Using table below select the proper package and the

amount of copper board needed.

Since the US1150 has separate pins for the output (Vout)

and the sense (Vsense), it is ideal for providing true re-

mote sensing of the output voltage at the load.This

means that the voltage drops due to parasitic resistance

such as PCB traces between the regulator and the load

are compensated for using remote sensing. Figure 3

shows a typical application of the US1150 with remote

sensing.

Vin

Vout

Vin

US1150

Pkg

Copper qJA(°C/W)

Area

Max Pd Max Pd

Vctrl

Vsense

Vctrl

(Ta=25°C)

4.4W

3.7W

3.1W

2.4W

2.0W

(Ta=45°C)

3.6W

Adj

TO263 1.4"X1.4"

TO263 1.0"X1.0"

TO263 0.7"X0.7"

TO263 Pad Size

3.0W

2.6W

2.0W

1.63W

1150app3-1.0

SO8

1.0"X1.0"

Note: Above table is based on the maximum junction

temperature of 135°C.

As shown in the above table, any of the two packages

will do the job. For low cost applications the SO8 pack-

age is recommended.

Figure 3 - Schematic showing connection for best

load regulation

Stability

The US1150 requires the use of an output capacitor as

part of the frequency compensation in order to make the

regulator stable. Typical designs for the microproces-

sor applications use standard electrolytic capacitors with

typical ESR in the range of 50 to 100 mW and an output

capacitance of 500 to 1000uF. Fortunately as the ca-

pacitance increases, the ESR decreases resulting in a

fixed RC time constant. The US1150 takes advantage of

this phenomena in making the overall regulator loop

stable.

Rev. 1.2

10/28/99

2-5

US1150CM [UNISEM]

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