SC8863-250CSKTR SEMTECH [Semtech Corporation], SC8863-250CSKTR Datasheet - Page 8

• Manufacturer Part Number: SC8863-250CSKTR
• Description: 150mA Ultra Low Dropout, Low Noise Regulator
• Manufacturer: SEMTECH [Semtech Corporation]

1% tolerance resistors are recommended. The values of
R1 and R2 should be selected such that the current flow
through them is 10µA (thus R2
voltages and/or high output currents, stability may be
improved by increasing C2 to 2.2µF and reducing R2 to
10k . See “Component Selection - General” for input
capacitor requirements.
Thermal Considerations
The worst-case power dissipation for this part is given
by:
For all practical purposes, it can be reduced to:
Looking at a typical application:
V
V
I
T
This gives us:
Using this figure, we can calculate the maximum thermal
impedance allowable to maintain T
P
P
P
POWER MANAGEMENT
Applications Information (Cont.)
θ
OUT
A
IN(MAX)
OUT
D
D
D
J (
2005 Semtech Corp.
(
(
(
= 85°C
−
MAX
MAX
MAX
A
= 150mA
= (3 - 3.5%) = 2.895V worst-case
)(
MAX
)
)
)
= 4.2V
=
=
=
)
(
(
(
V
V
4
=
2 .
IN
IN
(
(
(
T
MAX
MAX
−
( J
MAX
. 2
)
)
P
895
−
−
)
D
V
V
(
−
MAX
OUT
OUT
)
T
•
A
)
(
(
. 0
(
MIN
MIN
MAX
150
)
)
)
)
)
)
•
•
=
I
I
=
OUT
OUT
(
196
150
(
(
. 0
MAX
MAX
196
mW
−
)
)
120k ). At high input
J
85
+
V
)
150°C:
IN
=
(
MAX
332
)
•
°
C
I
Q
(
/
MAX
W
)
8
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
SC8863 is 256°C/W. Thus with no additional heatsinking,
T
The junction temperature can be reduced further by the
use of larger trace widths, and connecting pcb copper
area to the GND pin (pin 2), which connectes directly to
the device substrate. Adding approximately one square
inch of pcb copper to pin 2 will reduce
approximately 130°C/W and T
110°C, for example. Lower junction temperatures
improve overall output voltage accuracy. A sample pcb
layout for the Internally Preset Output Voltage circuit on
page 1 is shown in Figure 2 on page 9.
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. See Figure 2 on page 9 for
a sample layout.
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 and output capacitors close to the
device for optimal transient response and device
behavior.
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)
= 135°C.
J(MAX)
to approximately
SC8863
www.semtech.com
TH(J-A)
to