lt3011emse Linear Technology Corporation, lt3011emse Datasheet - Page 11

• Manufacturer Part Number: lt3011emse
• Description: 50ma, 3v To 80v Low Dropout Micropower Linear Regulator With Pwrgd
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
During normal operation, an internal glitch fi lter will ignore
short transients (<15μs). Longer transients below the 90%
threshold will reset the JK fl ip-fl op. This fl ip-fl op ensures
that the capacitor on the C
the way to the V
time delay. This provides a consistent time delay after the
ADJ pin is within 10% of the regulated voltage before the
PWRGD pin switches to high impedance.
Thermal Considerations
The power handling capability of the device will be limited by
the maximum rated junction temperature (125°C, LT3011E/
LT3011I or 150°C, LT3011H). The power dissipated by the
device will be made up of two components:
1. Output current multiplied by the input/output voltage
2. GND pin current multiplied by the input voltage:
The GND pin current is found by examining the GND pin
current curves in the Typical Performance Characteristics
section. Power dissipation will be equal to the sum of the
two components listed above.
The LT3011 series regulators have internal thermal limiting
designed to protect the device during overload conditions.
For continuous normal conditions, the maximum junction
temperature rating of 125°C (LT3011E/ LT3011I) or 150°C
(LT3011H) 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.
ADJ
V
REF
differential: I
I
• 90%
GND
• V
+
–
IN
Figure 4. PWRGD Circuit Block Diagram
OUT
CT(LOW)
• (V
J
K
IN
Q
threshold before restarting the
– V
T
I
CT
pin is quickly discharged all
OUT
3μA
–
+
) and,
C
V
T
CT(LOW)
0.1V
V
– V
( 1.1V)
CT(HIGH)
BE
3011 F04
PWRGD
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with one ounce
copper.
Table 1. MSOP Measured Thermal Resistance
Table 2. DFN Measured Thermal Resistance
The thermal resistance junction-to-case (θ
at the Exposed Pad on the back of the die, is 16°C/W.
Continuous operation at large input/output voltage dif-
ferentials and maximum load current is not practical due
to thermal limitations. Transient operation at high input/
output differentials is possible. The approximate thermal
time-constant for a 2500sq mm 3/32" FR-4 board, with
maximum topside and backside area for one ounce cop-
per, is three seconds. This time-constant will increase as
more thermal mass is added (i.e., vias, larger board and
other components).
For an application with transient high power peaks, average
power dissipation can be used for junction temperature
calculations as long as the pulse period is signifi cantly less
than the thermal time constant of the device and board.
2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm
225 sq mm
100 sq mm
225 sq mm
100 sq mm
TOPSIDE
TOPSIDE
COPPER AREA
COPPER AREA
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
BACKSIDE
BACKSIDE
BOARD AREA
BOARD AREA
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
THERMAL RESISTANCE
JC
52°C/W
54°C/W
58°C/W
64°C/W
52°C/W
54°C/W
58°C/W
64°C/W
LT3011
), measured
11
3011f