LT1521CS8 Linear Technology, LT1521CS8 Datasheet - Page 10

• Manufacturer Part Number: LT1521CS8
• Description: IC LDO REG W/SHTDWN ADJ 8-SOIC
• Manufacturer: Linear Technology

Specifications of LT1521CS8

• Regulator Topology: Positive Adjustable
• Voltage - Output: 3.8 ~ 20 V
• Voltage - Input: 4.3 ~ 20 V
• Voltage - Dropout (typical): 0.5V @ 300mA
• Number Of Regulators: 1
• Current - Output: 300mA
• Current - Limit (min): 320mA
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
LT1521/LT1521-3
LT1521-3.3/LT1521-5
10
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
an output current change of 1mA to 300mA is –20mV
typical at V
would be:
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
2. Ground pin current multiplied by the input voltage:
(12V/3.75V)(– 20mV) = – 64mV
differential: I
(I
V
V
I
OUTPUT RANGE = 3.75V TO 20V
ADJ
GND
OUT
ADJ
= 50nA AT 25 C
= 3.75V
= 3.75V 1 +
)(V
IN
OUT
OUT
)
V
Figure 2. Adjustable Operation
IN
R2
R1
OUT
/3.75V). For example: load regulation for
= 3.75V. At V
+ (I
(V
U
ADJ
IN
SHDN
IN
+ R2)
– V
INFORMATION
U
LT1521
GND
OUT
OUT
), and
OUT
ADJ
= 12V, load regulation
W
R2
R1
+
U
LT1521 • F01
V
OUT
The ground pin current can be found by examining the
Ground Pin Current curves in the Typical Performance
Characteristics. Power dissipation will be equal to the sum
of the two components listed above.
The LT1521 series regulators have internal thermal limit-
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
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
* Pin 4 is ground. ** Device is mounted on topside.
Table 2. S8 Package*
* Pins 3, 6, 7 are ground. ** Device is mounted on topside.
TOPSIDE**
2500mm
1000mm
TOPSIDE** BACKSIDE
2500mm
1000mm
225mm
100mm
225mm
100mm
COPPER AREA
COPPER AREA
2
2
2
2
2
2
2
2
BACKSIDE
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2
2
2
2
2
2
2
2
BOARD AREA
BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2
2
2
2
2
2
2
2
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
THERMAL RESISTANCE
60 C/W
60 C/W
68 C/W
74 C/W
110 C/W
115 C/W
120 C/W
130 C/W
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