Moteur de recherche de fiches techniques de composants électroniques
  French  ▼

Delete All
ON OFF
ALLDATASHEET.FR

X  

Preview PDF Download HTML

US1176 Fiches technique(PDF) 5 Page - UNISEM

No de pièce US1176
Description  7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT
Download  5 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Fabricant  UNISEM [UNISEM]
Site Internet  
Logo UNISEM - UNISEM

US1176 Fiches technique(HTML) 5 Page - UNISEM

  US1176 Datasheet HTML 1Page - UNISEM US1176 Datasheet HTML 2Page - UNISEM US1176 Datasheet HTML 3Page - UNISEM US1176 Datasheet HTML 4Page - UNISEM US1176 Datasheet HTML 5Page - UNISEM  
Zoom Inzoom in Zoom Outzoom out
 5 / 5 page
background image
US1176
2-5
Rev. 1.1
9/24/99
The US1176 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 US1176 is 10
mA , R1 is typically selected to be a 121
Ω 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.
Load Regulation
Since the US1176 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 US1176 with remote
sensing.
Figure 3 - Schematic showing connection for best
load regulation
Stability
The US1176 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 m
Ω 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 US1176 takes advantage of
this phenomena in making the overall regulator loop
stable.
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.
Shutdown Operation
The US1176 can be disabled by pulling the S.D pin low
using an open collector device such as a low cost 2N3904
general purpose transistor as shown in the application
circuit. The current sink of the pin is equal to:
Isink=(Vctrl-1.4)/R where, R=50 k
Ω typ.
Thermal Design
The US1176 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.
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.
Pkg
Copper
θJA(°C/W)
Max Pd
Max Pd
Area
(Ta=25
°C)
(Ta=45
°C)
M or P 1.4"X1.4"
25
4.4W
3.6W
M or P 1.0"X1.0"
30
3.7W
3.0W
M or P 0.7"X0.7"
35
3.1W
2.6W
M or P Pad Size
45
2.4W
2.0W
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 lower cost applications the Power
Flex package is recommended.
1176app3-1.0
R1
R2
Vin
Vctrl
RL
US1176
Vsense
Adj
Vout
Vctrl
Vin


Html Pages

1  2  3  4  5 


Fiches technique Télécharger

Go To PDF Page


Lien URL




Politique de confidentialité
ALLDATASHEET.FR
ALLDATASHEET vous a-t-il été utile ?  [ DONATE ] 

À propos de Alldatasheet   |   Publicité   |   Contactez-nous   |   Politique de confidentialité   |   Echange de liens   |   Fabricants
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn