IC LDO REG W/SHTDWN 3.3V 8-SOIC

LT1521CS8-3.3#TRPBF

Manufacturer Part NumberLT1521CS8-3.3#TRPBF
DescriptionIC LDO REG W/SHTDWN 3.3V 8-SOIC
ManufacturerLinear Technology
LT1521CS8-3.3#TRPBF datasheet
 


Specifications of LT1521CS8-3.3#TRPBF

Regulator TopologyPositive FixedVoltage - Output3.3V
Voltage - Input4.3 ~ 20 VVoltage - Dropout (typical)0.5V @ 300mA
Number Of Regulators1Current - Output300mA
Current - Limit (min)320mAOperating Temperature0°C ~ 125°C
Mounting TypeSurface MountPackage / Case8-SOIC (3.9mm Width)
Lead Free Status / RoHS StatusLead free / RoHS Compliant  
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LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
U
APPLICATIONS
INFORMATION
IN
OUT
V
LT1521
IN
SHDN
ADJ
GND
R2
V
= 3.75V 1 +
+ (I
+ R2)
OUT
ADJ
R1
V
= 3.75V
ADJ
I
= 50nA AT 25 C
ADJ
OUTPUT RANGE = 3.75V TO 20V
Figure 2. Adjustable Operation
output is turned off and the divider current will be zero.
Curves of Adjust Pin Voltage vs Temperature and Adjust
Pin Bias Current vs Temperature appear in the Typical
Performance Characteristics. The reference voltage at the
adjust pin has a positive temperature coefficient of ap-
proximately 15ppm/ C. The adjust pin bias current has a
negative temperature coefficient. These effects will tend to
cancel each other.
The adjustable device is specified with the adjust pin tied
to the output pin. This sets the output voltage to 3.75V.
Specifications for output voltages greater than 3.75V will
be proportional to the ratio of the desired output voltage
to 3.75V; (V
/3.75V). For example: load regulation for
OUT
an output current change of 1mA to 300mA is –20mV
typical at V
= 3.75V. At V
= 12V, load regulation
OUT
OUT
would be:
(12V/3.75V)(– 20mV) = – 64mV
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125 C). The
power dissipated by the device will be made up of two
components:
1. Output current multiplied by the input/output voltage
differential: I
(V
– V
), and
OUT
IN
OUT
2. Ground pin current multiplied by the input voltage:
(I
)(V
)
GND
IN
10
W
U
The ground pin current can be found by examining the
V
OUT
Ground Pin Current curves in the Typical Performance
+
R2
Characteristics. Power dissipation will be equal to the sum
of the two components listed above.
The LT1521 series regulators have internal thermal limit-
R1
ing designed to protect the device during overload condi-
tions. For continuous normal load conditions the maxi-
mum junction temperature rating of 125 C must not be
LT1521 • F01
exceeded. It is important to give careful consideration to
all sources of thermal resistance from junction to ambient.
Additional heat sources mounted nearby must also be
considered.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
The following tables list thermal resistance for each pack-
age. Measured values of thermal resistance for several
different board sizes and copper areas are listed for each
package. All measurements were taken in still air on
3/32" FR-4 board with one ounce copper. All NC leads were
connected to the ground plane.
Table 1. MS8 Package
COPPER AREA
TOPSIDE**
2
2500mm
2
1000mm
2
225mm
2
100mm
* Pin 4 is ground. ** Device is mounted on topside.
Table 2. S8 Package*
COPPER AREA
TOPSIDE** BACKSIDE
2
2500mm
2
1000mm
2
225mm
2
100mm
* Pins 3, 6, 7 are ground. ** Device is mounted on topside.
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
BACKSIDE
BOARD AREA
2
2
2500mm
2500mm
110 C/W
2
2
2500mm
2500mm
115 C/W
2
2
2500mm
2500mm
120 C/W
2
2
2500mm
2500mm
130 C/W
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2
2
2500mm
2500mm
60 C/W
2
2
2500mm
2500mm
60 C/W
2
2
2500mm
2500mm
68 C/W
2
2
2500mm
2500mm
74 C/W
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