LT3020/LT3020-1.2/
LT3020-1.5/LT3020-1.8
W U U
APPLICATIO S I FOR ATIO
U
The LT3020 regulator has internal thermal limiting (with
hysteresis)designedtoprotectthedeviceduringoverload
conditions. For normal continuous conditions, do not
exceedthemaximumjunctiontemperatureratingof125°C.
Carefully consider all sources of thermal resistance from
junction to ambient including other heat sources mounted
in proximity to the LT3020.
Calculating Junction Temperature
Example: Given an output voltage of 1.8V, an input voltage
range of 2.25V to 2.75V, an output current range of 1mA
to 100mA, and a maximum ambient temperature of 70°C,
what will the maximum junction temperature be for an
application using the DD package?
The power dissipated by the device is equal to:
TheundersideoftheLT3020DDpackagehasexposedmetal
(4mm2) from the lead frame to where the die is attached.
This allows heat to directly transfer from the die junction
to the printed circuit board metal to control maximum
operating junction temperature. The dual-in-line pin ar-
rangement allows metal to extend beyond the ends of the
package on the topside (component side) of a PCB. Con-
nectthismetaltoGNDonthePCB.ThemultipleINandOUT
pinsoftheLT3020alsoassistinspreadingheattothePCB.
IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)
where
)
IOUT(MAX) = 100mA
VIN(MAX) = 2.75V
IGND at (IOUT = 100mA, VIN = 2.75V) = 3mA
so
The LT3020 MS8 package has pin 4 fused with the lead
frame. This also allows heat to transfer from the die to the
printedcircuitboardmetal, thereforereducingthethermal
resistance. Copper board stiffeners and plated through-
holes can also be used to spread the heat generated by
power devices.
P = 100mA(2.75V – 1.8V) + 3mA(2.75V) = 0.103W
The thermal resistance is in the range of 35°C/W to
70°C/W depending on the copper area. So the junction
temperatureriseaboveambientisapproximatelyequalto:
0.103W(52.5°C/W) = 5.4°C
The maximum junction temperature equals the maximum
junction temperature rise above ambient plus the maxi-
mum ambient temperature or:
The following tables list thermal resistance for several
different board sizes and copper areas for two different
packages. Measurements were taken in still air on 3/32"
FR-4 board with one ounce copper.
TJMAX = 70°C + 5.4°C = 75.4°C
Table 1. Measured Thermal Resistance for DD Package
Protection Features
COPPER AREA
THERMAL RESISTANCE
TOPSIDE*
2500mm2
900mm2
225mm2
100mm2
50mm2
BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
The LT3020 incorporates several protection features that
make it ideal for use in battery-powered circuits. In addi-
tion to the normal protection features associated with
monolithic regulators, such as current limiting and ther-
mal limiting, the device also protects against reverse-
input voltages, reverse-output voltages and reverse
output-to-input voltages.
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
35°C/W
40°C/W
55°C/W
60°C/W
70°C/W
Table 2. Measured Thermal Resistance for MS8 Package
Current limit protection and thermal overload protection
protect the device against current overload conditions at
the output of the device. For normal operation, do not
exceed a junction temperature of 125°C.
COPPER AREA
TOPSIDE* BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2
1000mm2
225mm2
100mm2
50mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
110°C/W
115°C/W
120°C/W
130°C/W
140°C/W
The IN pins of the device withstand reverse voltages of
10V. The LT3020 limits current flow to less than 1µA and
no negative voltage appears at OUT. The device protects
both itself and the load against batteries that are plugged
*Device is mounted on topside.
in backwards.
sn3020 3020fas
11
Linear [ Linear ]
