lt3060 Linear Technology Corporation, lt3060 Datasheet - Page 15

• Manufacturer Part Number: lt3060
• Description: 45v Vin, Micropower, Low Noise, 100ma Low Dropout, Linear Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Table 2. DC Package, 8-Lead DFN
*Device is mounted on topside
Table 3. TS8 Package, 8 Lead TSOT-23
*Device is mounted on topside
Calculating Junction Temperature
Example: Given an output voltage of 2.5V, an input volt-
age range of 12V ±5%, an output current range of 0mA
to 50mA and a maximum ambient temperature of 85°C,
what will the maximum junction temperature be?
The power dissipated by the device equals:
where,
So,
Using a DFN package, the thermal resistance ranges from
48°C/W to 60°C/W depending on the copper area with
no thermal vias. So the junction temperature rise above
ambient approximately equals:
TOPSIDE*
TOPSIDE*
(mm
(mm
I
I
V
I
P = 50mA • (12.6V – 2.5V) + 0.6mA • 12.6V = 0.513W
0.513W • 54°C/W = 27.8°C
2500
1000
2500
1000
OUT(MAX)
OUT(MAX)
GND
225
100
225
100
50
50
IN(MAX)
COPPER AREA
COPPER AREA
2
2
)
)
at (I
BACKSIDE
BACKSIDE
= 12.6V
OUT
(mm
(mm
• (V
= 50mA
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2
2
= 50mA, V
IN(MAX)
)
)
BOARD AREA
BOARD AREA
–V
(mm
(mm
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
OUT
IN
2
2
)
)
= 12.6V) = 0.6mA
) + I
GND
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
THERMAL RESISTANCE
• V
IN(MAX)
48°C/W
49°C/W
50°C/W
54°C/W
60°C/W
57°C/W
58°C/W
59°C/W
63°C/W
67°C/W
The maximum junction temperature equals the maximum
ambient temperature plus the maximum junction tem-
perature rise above ambient or:
Protection Features
The LT3060 incorporates several protection features
that make it ideal for use in battery-powered circuits. In
addition to the normal protection features associated with
monolithic regulators, such as current limiting and thermal
limiting, the device also protects against reverse-input
voltages, reverse-output voltages and reverse output-to-
input voltages.
Current limit protection and thermal overload protection
protect the device against current overload conditions at
the output of the device. The typical thermal shutdown
temperature is 165°C. For normal operation, do not exceed
a junction temperature of 125°C (LT3060E, LT3060I,
LT3060MP) or 150°C (LT3060H).
The LT3060 IN pin withstands reverse voltages up to 50V.
The device limits current fl ow to less than 300μA (typically
less than 50μA) and no negative voltage appears at OUT.
The device protects both itself and the load against batteries
that are plugged in backwards.
The SHDN pin cannot be driven below GND unless tied to
the IN pin. If the SHDN pin is driven below GND while IN is
powered, the output may turn on. SHDN pin logic cannot
be referenced to a negative supply voltage.
The LT3060 incurs no damage if its output is pulled below
ground. If the input is left open-circuit or grounded, the
output can be pulled below ground by 50V. No current
fl ows through the pass transistor from the output.
However, current fl ows in (but is limited by) the resistor
divider that sets the output voltage. Current fl ows from
the bottom resistor in the divider and from the ADJ pin’s
internal clamp through the top resistor in the divider to
the external circuitry pulling OUT below ground. If the
input is powered by a voltage source, the output sources
current equal to its current limit capability and the LT3060
protects itself by thermal limiting. In this case, grounding
the SHDN pin turns off the device and stops the output
from sourcing current.
T
JMAX
= 85°C + 27.8°C = 112.8°C
LT3060
15
3060f