LT3022 Datasheet, PDF (12/16 Pages) Linear Technology – 1A, 0.9V to 10V, Very Low Dropout Linear Regulator

LT3022
Applications Information
The following tables list thermal resistance as a function
of copper area in a fixed board size. All measurements are
taken in still air on a 4-layer FR-4 board with 1oz solid
internal planes, and 2oz external trace planes with a total
board thickness of 1.6mm. For more information on ther-
mal resistance and high thermal conductivity test boards,
refer to JEDEC standard JESD51, notably JESD51-12 and
JESD51-7. Achieving low thermal resistance necessitates
attention to detail and careful PCB layout.
Table 2. Measured Thermal Resistance for DHC Package
COPPER AREA
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm² 2500mm² 2500mm²
35°C/W
1000mm² 2500mm² 2500mm²
37°C/W
225mm² 2500mm² 2500mm²
38°C/W
100mm² 2500mm² 2500mm²
40°C/W
*Device is mounted on topside
Table 3. Measured Thermal Resistance for MSE Package
COPPER AREA
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm² 2500mm² 2500mm²
35°C/W
1000mm² 2500mm²
225mm² 2500mm²
2500mm²
2500mm²
37°C/W
38°C/W
100mm² 2500mm² 2500mm²
40°C/W
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 1.5V, an input voltage
range of 1.7V to 1.9V, an output load current range of 1mA
to 1A and a maximum ambient temperature of 85°C, what
is the maximum junction temperature for an application
using the DHC package?
The power dissipated by the device equals:
I_LOAD(MAX) • (V_IN(MAX) – V_OUT) + I_GND • (V_IN(MAX))
where:
I_LOAD(MAX) = 1A
V_IN(MAX) = 1.9V
I_GND at (I_LOAD = 1A, V_IN = 1.9V) = 18mA
so:
P = 1A • (1.9V – 1.5V) + 18mA • (1.9V) = 0.434W
12
The thermal resistance is about 38°C/W depending on
the copper area. So the junction temperature rise above
ambient is approximately equal to:
0.434W • (38°C/W) = 16.5°C
The maximum junction temperature equals the maximum
junction temperature rise above ambient plus the maximum
ambient temperature or:
T_JMAX = 85°C + 16.5°C = 101.5°C
Protection Features
The LT3022 incorporates several protection features that
make it ideal for use in battery-powered circuits. In ad-
dition 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 its
output. For normal operation, do not exceed 125°C junction
temperature. The typical thermal shutdown temperature
is 165°C and the thermal shutdown circuit incorporates
about 7°C of hysteresis.
The IN pins withstand reverse voltages of 10V. The LT3022
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 in backwards.
The LT3022 incurs no damage if OUT is pulled below
ground. If IN is left open-circuited or grounded, OUT can
be pulled below ground by 10V. No current flows from the
pass transistor connected to OUT. However, current flows
in (but is limited by) the resistor divider that sets the out-
put voltage. Current flows 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 IN is powered by a voltage source,
OUT sources current equal to its current limit capability
and the LT3022 protects itself by thermal limiting. In this
case, grounding SHDN turns off the LT3022 and stops
OUT from sourcing current.
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