sc1457isk-1.5tr Semtech Corporation, sc1457isk-1.5tr Datasheet - Page 6

• Manufacturer Part Number: sc1457isk-1.5tr
• Description: Sc1457 150 Ma Ultra-low Dropout Regulator With Undervoltage Flag
• Manufacturer: Semtech Corporation

Thermal Considerations
The worst-case power dissipation for this part is given
by:
For all practical purposes, equation (1) can be reduced
to the following expression:
Looking at a typical application, 3.3V to 2.8V at 150mA:
V
V
I
T
Inserting these values into equation (2) gives us:
Using this figure, we can calculate the maximum thermal
impedance allowable to maintain T
P
POWER MANAGEMENT
P
P
OUT
Applications Information (Cont.)
A
IN(MAX)
OUT(MIN)
D
D
D
JA
2004 Semtech Corp.
(
(
(
= 85°C
MAX
MAX
MAX
(
MAX
= 150mA
)
)
)
)
= 3.3 + 5% = 3.465V
= 2.8V - 2% = 2.744V
V
V
. 3
T
IN
IN
465
( J
(
(
MAX
MAX
MAX
P
)
)
)
D
(
. 2
MAX
V
V
T
744
OUT
OUT
A
)
(
MAX
(
(
MIN
MIN
)
. 0
)
)
150
I
I
125
OUT
OUT
. 0
(
(
108
MAX
MAX
108
85
)
)
J
mW
V
125°C:
IN
370
(
MAX
)
C
I
/
Q
W
(
MAX
)
(1)
(2)
6
With the standard SOT-23-5/TSOT-23-5 Land Pattern
shown at the end of this datasheet, and minimum trace
widths, the thermal impedance junction to ambient for
SC1457ISK is 256°C/W. Thus no additional heatsinking
is required for this example.
The junction temperature can be reduced further (or
higher power dissipation can be allowed) by the use of
larger trace widths and connecting PCB copper to the
GND pin (pin 2), which connects directly to the device
substrate. Adding approximately one square inch of PCB
copper to pin 2 will reduce
130°C/W and T
approximately 100°C for the SOT-23-5 package. The use
of multi layer boards with internal ground/power planes
will lower the junction temperature and improve overall
output voltage accuracy.
Layout Considerations
While layout for linear devices is generally not as critical
as for a switching application, careful attention to detail
will ensure reliable operation.
1) Attaching the part to a larger copper footprint will
enable better heat transfer from the device, especially
on PCBs where there are internal ground and power
planes.
2) Place the input, output and bypass capacitors close
to the device for optimal transient response and device
behaviour.
3) Connect all ground connections directly to the ground
plane. If there is no ground plane, connect to a common
local ground point before connecting to board ground.
J(MAX)
for the example above to
JA
to approximately
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SC1457