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PDF US1050 Data sheet ( Hoja de datos )

Número de pieza US1050
Descripción 5A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
Fabricantes UNISEM 
Logotipo UNISEM Logotipo



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No Preview Available ! US1050 Hoja de datos, Descripción, Manual

FEATURES
Guaranteed < 1.3V Dropout at Full Load
Current
Fast Transient Response
1% Voltage Reference Initial Accuracy
Output Current Limiting
Built-in Thermal Shutdown
APPLICATIONS
Low Voltage Processor Applications such as :
P54C,P55C,Cyrix M2,
POWER PC,AMD
GTL+ Termination
PENTIUM PRO, KLAMATH
Low Voltage Memory Termination Applications
Standard 3.3V Chip-Set and Logic Applications
US1050
5A LOW DROPOUT POSITIVE
ADJUSTABLE REGULATOR
DESCRIPTION
The US1050 product is a low dropout three terminal ad-
justable regulator with minimum of 5A output current
capability. This product is specifically designed to pro-
vide well regulated supply for low voltage IC applications
such as PentiumP54C,P55Cas well as GTL+
termination for Pentium Proand Klamathpro-
cessor applications . The US1050 is also well suited for
other processors such as Cyrix,AMD and Power
PCapplications. The US 1050 is guaranteed to have
<1.3V drop out at full load current making it ideal to
provide well regulated outputs of 2.5V to 3.6V with 4.75V
to 7V input supply.
TYPICAL APPLICATION
5V
C1
1500uF
Vin 3
US1050 Vout 2
Adj 1
3.38V / 5A
R1
121
C2
R2 2x 1500uF
205
1050app1-1.1
Typical Application of US1050 in a 5V to 3.38V regulator designed
to meet the Intel P54C Processors.
Notes: Pentium P54C,P55C ,Klamath,Pentium Pro,VRE,are trade marks of Intel Corp.Cyrix M2 is trade mark of Cyrix Corp.
Power PC is trade mark of IBM Corp.
PACKAGE ORDER INFORMATION
Tj (°C)
0 TO 150
3 PIN PLASTIC
TO220 (T)
US1050CT
3 PIN PLASTIC
TO263 (M)
US1050CM
2 PIN PLASTIC
POWER FLEX (P)
US1050CP
3 PIN PLASTIC
TO252 (D)
US1050CD
Rev. 1.3
10/27/00
2-33

1 page




US1050 pdf
US1050
Thermal Design
T=Temperature Rise Above Ambient
The US1050 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
shows the steps in selecting the proper Regulator heat
sink for the worst case current consumption using Intel
200MHz microprocessor as the load .
Assuming the following specifications :
θSA = T
PD
θSA = 81 =11.7 ° C/W
6.9
5) Next , a heat sink with lower θsa than the one calcu-
lated in step 4 must be selected. One way to do this is
to simply look at the graphs of the “Heat Sink Temp
Rise Above the Ambient” vs. the “Power Dissipation” and
select a heat sink that results in lower temperature rise
than the one calculated in previous step. The following
heat sinks from AAVID and Thermaloy meet this crite-
ria.
VIN =5V
VO =3.5V
IOUTMAX =4.6A
TA =35° C
Thermalloy
AAVID
0
6021PB
534202B
Air Flow (LFM)
100 200
300
6021PB 6073PB 6109PB
534202B 507302 575002
400
7141D
576802B
The steps for selecting a proper heat sink to keep the
junction temperature below 135°C is given as :
1) Calculate the maximum power dissipation using :
( )PD = IO UT× VINVO UT
PD =4.6×(53.5) =6.9 W
Note : For further information regarding the above com-
panies and their latest product offerings and application
support contact your local representative or the num-
bers listed below:
AAVID
Thermalloy
PH# (603) 528 3400
PH# (214) 243-4321
2) Select a package from the Regulator data sheet
and record its junction to case (or Tab) thermal
resistance.
Selecting TO220 package gives us :
θJC =2.7° C/W
3) Assuming that the heat sink is Black Anodized, cal-
culate the maximum Heat sink temperature allowed :
Assume , θcs=0.05°C/W (Heat sink to Case thermal
resistance for Black Anodized)
( )TS=TJPD × θJC + θCS
TS =1356.9×(2.7+0.05) =116 ° C
4) With the maximum heat sink temperature calcu-
lated in the previous step, the Heat Sink to Air thermal
resistance (θsa) is calculated by first calculating the
temperature rise above the ambient as follows :
T = TS TA =11635=81 ° C
Designing for Microprocessor Applications
As it was mentioned before the US1050 is designed spe-
cifically to provide power for the new generation of the
low voltage processors requiring voltages in the range
of 2.5V to 3.6V generated by stepping down the
5V supply. These processors demand a fast regulator
that supports their large load current changes. The worst
case current step seen by the regulator is anywhere in
the range of 1 to 7A with the slew rate of 300 to 500 nS
which could happen when the processor transitions from
“Stop Clock” mode to the “Full Active” mode. The load
current step at the processor is actually much faster ,in
the order of 15 to 20 nS,however the decoupling capaci-
tors placed in the cavity of the processor socket handle
this transition until the regulator responds to the load
current levels. Because of this requirement the selec-
tion of high frequency low ESR and low ESL output ca-
pacitor is imperative in the design of these regulator cir-
cuits.
Figure 4 shows the effects of a fast transient on the
Rev. 1.3
10/27/00
2-37

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