LT1573CS8 Linear Technology, LT1573CS8 Datasheet - Page 10

• Manufacturer Part Number: LT1573CS8
• Description: IC LDO REGULATOR DVR ADJ 8-SOIC
• Manufacturer: Linear Technology
• Type: Positive Adjustabler

Specifications of LT1573CS8

• Number Of Outputs: 1
• Voltage - Output: 1.27 ~ 6.8 V
• Current - Supply: 1.7mA
• Voltage - Input: 2.8 ~ 10 V
• Operating Temperature: 0°C ~ 125°C
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LT1573
Thermal Considerations
The thermal characteristics of several components need
to be considered; the LT1573, the pass transistor and
resistor R
on the worst-case conditions seen by each component
during normal operation.
1. Power Dissipation of the LT1573: The worst-case
10
power dissipation in the LT1573 is a function of drive
current, supply voltage and the value of R
dissipation for the LT1573 occurs when the drive cur-
rent is equal to approximately one half of its maximum
value. The worst-case power dissipation in the LT1573
can be calculated by the following formula:
where,
V
V
Following the previous design example for selecting
resistor R
lated from Eq (2):
For some operating conditions R
a short. This is possible in applications where the
operating requirements (input voltage and drive cur-
rent) are at the low end and the output will not be
shorted. For R
to calculate the maximum power dissipation in the
LT1573:
where,
V
V
I
DRIVE
IN
BE
IN
BE
P
P
R
P
= the maximum input voltage to the circuit
= the maximum input voltage
D
D
= the minimum emitter/base voltage of the PNP
D
= the minimum emitter/base voltage of the PNP
D
pass transistor
= (V
= the required maximum drive current
D
. Power dissipation should be calculated based
minimum R for latch - off function
V
5 5 0 65
D
IN
IN
, the power dissipation of LT1573 is calcu-
4 24
4
– V
R
D
V
D
= 0, the following formula may be used
BE
BE
U
)(I
2
2
DRIVE
D
U
0 25
)
W
D
W
may be replaced with
D
. Worst-case
U
(2)
(3)
2. Power Dissipation of the Resistor R
3. Power Dissipation of the PNP Transistor: The worst-
power dissipation in resistor R
so that the power rating of the resistor can be deter-
mined. The worst-case power dissipation in this resis-
tor will occur when the drive current is at a maximum.
The power dissipation can be calculated from the fol-
lowing formula:
where,
V
V
V
Following the previous design example, the power
dissipation of resistor R
case power dissipation in the PNP pass transistor is
simply equal to:
where,
V
I
Following the previous design example, the power
dissipation of PNP transistor is calculated from Eq (5):
The LT1573 series regulators have internal thermal
limiting designed to protect the device during overload
conditions. For continuous normal load conditions,
the maximum 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. For surface mount devices, heat
sinking is accomplished by using the heat spreading
OUT
IN
BE
DRIVE
IN
P
P
P
P
= the maximum input voltage
= the maximum input voltage
RD
RD
PNP
PNP
= the minimum emitter/base voltage of the PNP
= the maximum output current
= the voltage at the LT1573 DRIVE pin
= V
= (V
= (5.5 – 3.3)(5) = 11W
V
5 5 0 65 0 39
SAT
IN
IN
of the DRIVE pin in the worst case
– V
V
BE
OUT
24
R
D
)(I
V
DRIVE
D
OUT
is calculated from Eq (4):
)
2
2
D
needs to be calculated
0 83
D
: The worst-case
W
(4)
(5)