US1010 - UNISEM - Pdf.Support

US1010

2-1

Rev. 1.3

10/30/00

TYPICAL APPLICATIONTYPICAL APPLICATION

DESCRIPTIONDESCRIPTION

The US1010 is a low dropout three terminal adjustable

regulator with minimum of 1A output current capability.

This product is specifically designed to provide well regu-

lated supply for low voltage IC applications such as high

speed bus termination and low current 3.3V logic

supply. The US1010 is also well suited for other appli-

cations such as VGA and sound cards. The US 1010 is

guaranteed to have <1.3V drop out at full load cur-

rent making it ideal to provide well regulated outputs of

2.5V to 3.6V with 4.75V to 7V input supply.

FEATURESFEATURES

Guaranteed < 1.3V Dropout at Full Load

Current

Fast Transient Response

1% Voltage Reference Initial Accuracy

Built-in Thermal Shutdown

Available in SOT-223, D-PAK , Power Flex

and 8 pin SOIC Surface Mount Packages

APPLICATIONSAPPLICATIONS

VGA & Sound Card Applications

Low Voltage High Speed Termination Applications

Standard 3.3V Chip-Set and Logic Applications

1A LOW DROPOUT POSITIVE

ADJUSTABLE REGULATOR

Typical Application of US1010 in a 5V to 2.85V SCSI termination regulator .

PACKAGE ORDER INFORMATIONPACKAGE ORDER INFORMATION

Tj (°C) 2 PIN PLASTIC 3 PIN PLASTIC 2 PIN PLASTIC 8 PIN PLASTIC

TO252 (D) SOT223 (Y) POWER FLEX (P) SOIC (S)

0 TO 150 US1010CD US1010CY US1010CP US1010CS

PRELIMINARY DATASHEET

2.85V / 1A

121

154

10uF

22uF

US1010

1010app1-1.4

Vin

Vout

Adj

US1010

2-2 Rev. 1.3

10/30/00

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 voltage between Vin and Vout required to main-

tain regulation at Vout. It is measured when the output

voltage 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.

ABSOLUTE MAXIMUM RATINGSABSOLUTE MAXIMUM RATINGS

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

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

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

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

PACKAGE INFORMATIONPACKAGE INFORMATION

2 PIN PLASTIC TO252 ( D ) 3 PIN PLASTIC SOT223 ( Y ) 2 PIN PLASTIC PFLEX ( P ) 8 PIN PLASTIC SOIC (S)

θJA=70°C/W for 0.5" Sq pad θJA=90°C/W for 0.4" Sq pad θJA=70°C/W for 0.5" Sq pad θJA=55°C/W for 1" Sq pad

ELECTRICAL SPECIFICATIONSELECTRICAL SPECIFICATIONS

Unless otherwise specified, these specifications apply over, Cin=1uF, Cout=10uF, and Tj=0 to 150°C.Typical

values refer to Tj=25°C.

PARAMETER SYM TEST CONDITION MIN TYP MAX UNITS

Reference Voltage VREF Io=10mA,Tj=25°C,(Vin-Vo)=1.5V 1.243 1.250 1.257 V

Io=10mA, (Vin-Vo)=1.5V 1.237 1.250 1.263

Line Regulation Io=10mA,1.3V<(Vin-Vo)<7V 0.2 %

Load Regulation (note 1) Vin=3.3V,Vadj=0,10mA<Io<1A 0.4 %

Dropout Voltage

(note 2) ∆VONote 2 , Io=1A 1.1 1.3 V

Current Limit Vin=3.3V,dVo=100mV 1.1 A

Minimum Load Current Vin=3.3V,Vadj=0V 5 10 mA

(note 3)

Thermal Regulation 30 mS PULSE,Vin-Vo=3V,Io=1A 0.01 0.02 %/W

Ripple Rejection f=120HZ ,Co=25uF Tan

Io=0.5A,Vin-Vo=3V 60 70 dB

Adjust Pin Current IADJ Io=10mA,Vin-Vo=1.5V,Tj=25

Io=10mA,Vin-Vo=1.5V 55 120 uA

Adjust Pin Current Change Io=10mA,Vin-Vo=1.5V,Tj=25 0.2 5 uA

Temperature Stability Vin=3.3V,Vadj=0V,Io=10mA 0.5 %

Long Term Stability Tj=125°C,1000 Hrs 0.3 1 %

RMS Output Noise Tj=25°C 10hz<f<10khz 0.003 %Vo

FRONT VIEW

Adj

Tab is

Vout

Vin

TOP VIEW

Adj

Vout

Vin

Tab is

Vout

FRONT VIEW

Tab is

Vout

Adj

Vin

TOP VIEW

VoutAdj

Vin

Vout

US1010

2-3

Rev. 1.3

10/30/00

APPLICATION INFORMATIONAPPLICATION INFORMATION

Introduction

The US1010 adjustable Low Dropout (LDO) regulator is

a 3 terminal device which can easily be programmed

with the addition of two external resistors to any volt-

ages within the range of 1.25 to 5.5 V.This regulator

unlike the first generation of the 3T regulators such as

LM117 that required 3V differential between the input

and the regulated output,only needs 1.3V differential to

maintain output regulation. This is a key requirement for

today’slow voltage IC applications that typically need

3.3V supply and are often generated from the 5V sup-

ply. Other applications such as high speed memory ter-

mination need to switch the load current from zero to full

load in tens of nanoseconds at the their pins ,which

translates to an approximately 300 to 500 nS current

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

erances are sometimes tight and they include the tran-

sient response as part of the specification.

The US1010 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 output capacitors.

PIN DESCRIPTIONSPIN DESCRIPTIONS

PIN # PIN SYMBOL PIN DESCRIPTION

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

2 Vout The output of the regulator. A minimum of 10uF capacitor must be connected

from this pin to ground to insure stability.

3 Vin 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 1.3V higher than Vout in order for the device to regulate properly.

BLOCK DIAGRAMBLOCK DIAGRAM

Figure 1 - Simplified block diagram of the US1010

Vin 3

1010blk1-1.0

1Adj

2Vout

THERMAL

SHUTDOWN

CURRENT

LIMIT

1.25V

US1010

2-4 Rev. 1.3

10/30/00

Output Voltage Setting

The US1010 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:

Figure 2 - Typical application of the US1010

for programming the output voltage.

The US1010 keeps a constant 1.25V between the out-

put pin and the adjust pin. By placing a resistor R1 across

these two pins a constant current flows through R1, add-

ing to the Iadj current and into the R2 resistor producing

a voltage equal to the (1.25/R1)*R2 + Iadj*R2 which will

be 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 US1010 is 10 mA , R1 is

typically selected to be 121Ω resistor so that it auto-

matically satisfies the minimum current requirement.

Notice that since Iadj is typically in the range of 50uA it

only adds a small error to the output voltage and should

only be considered when a very precise output voltage

setting is required. For example, in a typical 3.3V appli-

cation where R1=121Ω and R2=200Ω the error due to

Iadj is only 0.3% of the nominal set point.

Load Regulation

Since the US1010 is only a 3 terminal device , it is not

possible to provide true remote sensing of the output

voltage at the load.Figure 3 shows that the best load

Figure 3 - Schematic showing connection for best load

regulation

Stability

The US1010 requires the use of an output capacitor as

part of the frequency compensation in order to make the

regulator stable. Typical designs for microprocessor ap-

plications use standard electrolytic capacitors with a

typical ESR in the range of 50 to 100 mΩ 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 US1010 takes advantage of

this phenomena in making the overall regulator loop

stable.For most applications a minimum of 100uF alu-

minum electrolytic capacitor such as Sanyo MVGX se-

ries ,Panasonic FA series as well as the Nichicon PL

series insures both stability and good transient response.

regulation is achieved when the bottom side of R2 is

connected to the load and the top side of R1 resistor is

connected directly to the case or the Vout pin of the

regulator and not to the load. In fact , if R1 is connected

to the load side, the effective resistance between the

regulator and the load is gained up by the factor of (1+R2/

R1) ,or the effective resistance will be ,Rp(eff)=Rp*(1+R2/

R1).It is important to note that for high current applica-

tions, this can represent a significant percentage of the

overall load regulation and one must keep the path from

the regulator to the load as short as possible to mini-

mize this effect.

V V R

RIR

Where : V Typically

Illy

Rin figure

OUT REF ADJ

REF

ADJ

= +









+ ×1

125

50 2

1 2

V =.

= uA Typica

& R as shown

Vout

1010app2-1.0

Vin

Vref

IAdj = 50uA

US1010

Adj

VoutVin

1010app3-1.0

Vin

PARASITIC LINE

RESISTANCE

US1010

Adj

VoutVin

US1010

2-5

Rev. 1.3

10/30/00

Thermal Design

The US1010 incorporates an internal thermal shutdown

that protects the device when the junction temperature

exceeds the maximum allowable 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 continuous load operation the junction tempera-

ture is kept below this number. The example below for

a SCSI terminator application shows the steps in se-

lecting the proper regulator in a surface mount pack-

age .(See US1015 for non surface mount packages)

Assuming the following specifications :

Where ; VF is the forward voltage drop of the D1diode

as shown in figure 4.

The steps for selecting the right package with proper

board area for heatsinking to keep the junction tem-

perature below 135°C is given as :

1) Calculate the maximum power dissipation using :

2) Calculate the maximum θJA allowed for our ex-

ample:

2) Select a package from the datasheet with lower θJA

than the one calculated in the previous step.

Selecting TO252 (D Pak) with at least 0.5" square of

0.062" FR4 board using 1OZ copper has 70°C/W

which is lower than the calculated number.

(

)

( )

PIV V

P W

DOUT IN OUT

= × − −

= × − − =

08 5 0 5 285 132. . . .

JA JA

MAX

T T

=−

=−=°

135 35

756

. /

To set the output DC voltage, we need to select R1 and

R2 :

3) Assuming R1=121 Ω , 1%

Select R2=154 ΩΩ ,1%

V V

OUT

MAX

285

0 8

VOUT

REF

21121 285

125 1121= −









× = −









× =

.154.8 Ω

Figure 4 - Final Schematic for half of the

GTL+ termination regulator.

2.85V

1010app4-1.3

121

154

22uF

10uF US1010

Adj

VoutVin

Layout Consideration

The output capacitors must be located as close to

the Vout terminal of the device as possible. It is recom-

mended to use a section of a layer of the PC board as a

plane to connect the Vout pin to the output capacitors to

prevent any high frequency oscillation that may result

due to excessive trace inductance.