LT3022-1.8_15 Datasheet, PDF (14/20 Pages) Linear Technology – 1A, 0.9V to 10V, Very Low Dropout Linear Regulator

LT3022/LT3022-1.2
LT3022-1.5/LT3022-1.8
APPLICATIONS INFORMATION
To eliminate this problem, the LT3022 incorporates a
no-load or light load recovery circuit. This circuit is a
voltage-controlled current sink that significantly improves
the light load transient response time by discharging the
output capacitor quickly and then turning off. The current
sink turns on when the output voltage exceeds 6.5% of
the nominal output voltage. The current sink level is then
proportional to the overdrive above the threshold up to a
maximum of about 24mA. Consult the curve in the Typical
Performance Characteristics for the No-Load Recovery
Threshold.
If external circuitry forces the output above the no-load
recovery circuit’s threshold, the current sink turns on in
an attempt to restore the output voltage to nominal. The
current sink remains on until the external circuitry releases
the output. However, if the external circuitry pulls the output
voltage above the input voltage or the input falls below the
output, the LT3022 turns the current sink off and shuts
down the bias current/reference generator circuitry.
Thermal Considerations
The LT3022’s maximum rated junction temperature of
125°C limits its power handling capability. Two components
comprise the power dissipation of the device:
1. Output current multiplied by the input-to-output voltage
differential:
(I_LOAD) • (V_IN – V_OUT) and
2. GND pin current multiplied by the input voltage:
(I_GND) • (V_IN)
GND pin current is found by examining the GND pin current
curves in the Typical Performance Characteristics. Power
dissipation equals the sum of the two components listed.
The LT3022’s internal thermal limiting (with hysteresis)
protects the device during overload conditions. For normal
continuous conditions, do not exceed the maximum
junction temperature rating of 125°C. Carefully consider
all sources of thermal resistance from junction to ambient
including other heat sources mounted in proximity to the
LT3022.
The underside of the LT3022 DHC and MSE packages has
exposed metal from the lead frame to the die attachment.
Heat transfers directly from the die junction to the
printed circuit board metal, allowing maximum junction
temperature control. The dual-in-line pin arrangement
allows metal to extend beyond the ends of the package
on the topside (component side) of a PCB. Connect this
metal to GND on the PCB. The multiple IN and OUT pins
of the LT3022 also assist in spreading heat to the PCB.
Copper board stiffeners and plated throughholes can also
be used to spread the heat generated by power devices.
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 thermal
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
TOPSIDE*
2500mm²
1000mm²
225mm²
100mm²
BACKSIDE
2500mm²
2500mm²
2500mm²
2500mm²
BOARD AREA
2500mm²
2500mm²
2500mm²
2500mm²
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
35°C/W
37°C/W
38°C/W
40°C/W
*Device is mounted on topside
Table 3. Measured Thermal Resistance for MSE Package
COPPER AREA
TOPSIDE*
2500mm²
1000mm²
225mm²
100mm²
BACKSIDE
2500mm²
2500mm²
2500mm²
2500mm²
BOARD AREA
2500mm²
2500mm²
2500mm²
2500mm²
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
35°C/W
37°C/W
38°C/W
40°C/W
*Device is mounted on topside.
3022fb
14