LT3071EUFD LINER [Linear Technology], LT3071EUFD Datasheet - Page 21

• Manufacturer Part Number: LT3071EUFD
• Description: 5A, Low Noise, Programmable Output, 85mV Dropout Linear Regulator with Analog Margining
• Manufacturer: LINER [Linear Technology]

ApplicAtions inFormAtion
With a high input voltage, a problem can occur where the
removal of an output short will not allow the output volt-
age to recover. Other regulators with current limit foldback
also exhibit this phenomenon, so it is not unique to the
LT3071. The load line for such a load may intersect the
output current curve at two points: normal operation and
the SOA restricted load current settings. A common situ-
ation is immediately after the removal of a short circuit,
but with a static load ≥ 1A. In this situation, removal of the
load or reduction of I
and allow V
Reverse Voltage
The LT3071 incorporates a circuit that detects if V
creases below V
a typical threshold of about (V
threshold is exceeded, this detector circuit turns off the
drive to the internal NMOS pass transistor, thereby turning
off the output. The output pulls low with the load current
discharging the output capacitance. This circuit’s intent
is to limit and prevent back-feed current from OUT to IN
if the input voltage collapses due to a fault or overload
condition.
Thermal Considerations
The LT3071’s maximum rated junction temperature of
125°C limits its power handling capability and is domi-
nated by the output current multiplied by the input/output
voltage differential:
I
The LT3071’s internal power and thermal limiting circuitry
protect it under overload conditions. For continuous nor-
mal load conditions, do not exceed the maximum junction
temperature of 125°C. Give careful consideration to all
sources of thermal resistance from junction to ambient.
OUT
• (V
IN
OUT
– V
to return to normal regulation.
OUT
OUT
. This reverse-voltage detector has
)
OUT
to <1A will clear this condition
IN
– V
OUT
) = –6mV. If the
IN
de-
This includes junction to case, case-to-heat sink interface,
heat sink resistance or circuit board to ambient as the
application dictates. Also, consider additional heat sources
mounted in proximity to the LT3071. The LT3071 is a surface
mount device and as such, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Surface mount heat sinks and
plated through-holes can also be used to spread the heat
generated by power devices. Junction-to-case thermal
resistance is specified from the IC junction to the bottom
of the case directly below the die. This is the lowest resis-
tance path for heat flow. Proper mounting is required to
ensure the best possible thermal flow from this area of the
package to the heat sinking material. Note that the exposed
pad is electrically connected to GND.
Table 3 lists thermal resistance as a function of copper
area in a fixed board size. All measurements were taken
in still air on a 4-layer FR-4 board with 1 oz solid internal
planes and 2 oz top/bottom external trace planes with a
total board thickness of 1.6mm. PCB layers, copper weight,
board layout and thermal vias affect the resultant thermal
resistance. For further 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 3, UFD Plastic Package, 28-Lead QFN
*Device is mounted on topside
TOPSIDE*
2500mm
1000mm
225mm
100mm
COPPER AREA
2
2
2
2
BACK SIDE
2500mm
2500mm
2500mm
2500mm
2
2
2
2
BOARD AREA
2500mm
2500mm
2500mm
2500mm
2
2
2
2
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
30°C/W
32°C/W
33°C/W
35°C/W
LT3071

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