Datasheet

LT3032 Series
19
3032fd
APPLICATIONS INFORMATION
If wiring modifi cations are not permissible for the applica-
tions, including series resistance between the power supply
and the input of the LT3032 also stabilizes the application.
As little as 0.1Ω to 0.5Ω, often less, is effective in damp-
ing the LC resonance. If the added impedance between
the power supply and the input is unacceptable, adding
ESR to the input capacitor also provides the necessary
damping of the LC resonance. However, the required ESR
is generally higher than the series impedance required.
Thermal Considerations
The power handling capability of the device is limited by
the maximum rated junction temperature (125°C). The
power dissipated by the device is made up of the follow-
ing components:
1. Output current of each side multiplied by the respective
input/output voltage differential: (I
OUT
)(V
IN
to V
OUT
),
and
2. GND pin current for each side multiplied by its input
voltage: (I
GND
)(V
IN
)
The GND pin current of each side is found by examining
the GND Pin Current curves in the Typical Performance
Characteristics. Total power dissipation equals the sum
for both channels of the components listed above.
The LT3032 has internal thermal limiting designed to pro-
tect each side of the regulator during overload conditions.
For continuous normal 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. Additional
heat sources mounted nearby must also be considered.
The LT3032 is a surface mount device and heat sinking is
accomplished by using the heat spreading capabilities of
the PC board and its copper traces. Copper board stiffen-
ers and plated through-holes can also be used to spread
the heat generated by power devices.
Note that the exposed pads (Pins 15 and 16) are elect-
rically connected to ground (GND) and the negative input
(INN) respectively.
The following table lists thermal resistance as a function
of copper area on a fi xed board size. All measurements
were taken in still air on a 4-layer FR-4 board with 1oz
solid internal planes and 2oz external trace planes with a
total fi nished board thickness of 1.6mm.
Table 3. DE Package, 14-Lead DFN
COPPER AREA
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE
2500mm
2
2500mm
2
2500mm
2
32°C/W
1000mm
2
2500mm
2
2500mm
2
33°C/W
225mm
2
2500mm
2
2500mm
2
38°C/W
100mm
2
2500mm
2
2500mm
2
43°C/W
*Device is mounted on topside
For further information on thermal resistance and using
thermal information, refer to JEDEC standard JESD51,
notably JESD51-12.
PCB layers, copper weight, board layout and thermal vias
affect the resultant thermal resistance. This table provides
thermal resistance numbers for best-case 4-layer boards
with 1oz internal and 2oz external copper. Modern, mul-
tilayer PCBs may not be able to achieve quite the same
level performance as found in this table.