LTC3026 LINER [Linear Technology], LTC3026 Datasheet - Page 11

• Manufacturer Part Number: LTC3026
• Description: 1.5A Low Input Voltage VLDO Linear Regulator
• Manufacturer: LINER [Linear Technology]

OPERATIO
Boost Converter Component Selection
A 10µH chip inductor with a peak saturation current (I
of at least 150mA is recommended for use with the internal
boost converter. The inductor value can range between
4.7µH to 40µH, but values less than 10µH result in higher
switching frequency, increased switching losses, and
lower max output current available at the BST pin. See
Table 1 for a list of component suppliers.
It is also recommended that the BST pin be bypassed to
ground with a 4.7µF or greater ceramic capacitor. Larger
values of capacitance will not reduce the size of the BST
ripple much, but will decrease the ripple frequency pro-
portionally. The BST pin should maintain 1µF of capaci-
tance at all times to ensure correct operation (See “Output
Capacitance and Transient Response” section about ca-
pacitor selection). High ESR tantalum and electrolytic
capacitors may be used, but a low ESR ceramic must be
used in parallel for correct operation.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
majority of the power dissipated in the device will be the
output current multiplied by the input/output voltage
differential: (I
is less than 200µA even under heavy loads, so its power
consumption can be ignored for thermal calculations.
The LTC3026 has internal thermal limiting designed to
protect the device during momentary overload conditions.
For continuous normal conditions, the maximum junction
temperature rating of 125°C must not be exceeded. It is
Table 1. Inductor Vendor Information
SUPPLIER
Coilcraft
Murata
Taiyo Yuden
TDK
OUT
NLC252018T-100K
LQH2MCN100K02
)(V
U
PART NUMBER
0603PS-103KB
LB2016T100M
IN
– V
OUT
). Note that the BST current
WEBSITE
www.coilcraft.com
www.murata.com
www.t-yuden.com
www.TDK.com
SAT
)
important to give careful consideration to all sources of
thermal resistance from junction to ambient. Additional
heat sources mounted nearby must also be considered.
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.
A junction-to-ambient thermal coefficient of 40°C/W is
achieved by connecting the exposed pad of the MSOP or
DFN package directly to a ground plane of about 2500mm
Calculating Junction Temperature
Example: Given an output voltage of 1.2V, an input voltage
of 1.8V ±4%, an output current range of 0mA to 1A and a
maximum ambient temperature of 50°C, what will the
maximum junction temperature be?
The power dissipated by the device will be approximately:
where:
so:
Even under worst-case conditions LTC3026’s BST pin
power dissipation is only about 1mW, thus can be ig-
nored. The junction to ambient thermal resistance will be
on the order of 40°C/W. The junction temperature rise
above ambient will be approximately equal to:
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
I
I
V
P = 1A(1.87V – 1.2V) = 0.67W
0.67W(40°C/W) = 26.8°C
T
OUT(MAX)
OUT(MAX)
A
IN(MAX)
= 26.8°C + 50°C = 76.8°C
= 1.87V
(V
= 1A
IN(MAX)
– V
OUT
)
LTC3026
11
3026f
2
.