LM3410XMFE/NOPB National Semiconductor, LM3410XMFE/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM3410XMFE/NOPB
• Description: IC DRVR WT/OLED BCKLT SOT23-5
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Backlight, OLED, White LEDr

Specifications of LM3410XMFE/NOPB

• Constant Current: Yes
• Topology: PWM, SEPIC, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight, Flash/Torch
• Type - Secondary: High Brightness LED (HBLED), OLED, White LED
• Frequency: 1.2MHz ~ 2MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 3 V ~ 24 V
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 2.8A
• Internal Switch(s): Yes
• Efficiency: 88%
• For Use With: LM3410XSDSEPEV - BOARD EVALUATION FOR LM3410
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3410XMFE

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Total Power Losses are:
Calculating
We now know the internal power dissipation, and we are try-
ing to keep the junction temperature at or below 125°C. The
next step is to calculate the value for
actually very simple to accomplish, and necessary if you think
you may be marginal with regards to thermals or determining
what package option is correct.
The LM3410 has a thermal shutdown comparator. When the
silicon reaches a temperature of 165°C, the device shuts
down until the temperature drops to 150°C. Knowing this, one
can calculate the
cause the junction to top case thermal impedance is much
lower than the thermal impedance of junction to ambient air,
the error in calculating
you will need to attach a small thermocouple onto the top case
of the LM3410 to obtain the
Knowing the temperature of the silicon when the device shuts
down allows us to know three of the four variables. Once we
calculate the thermal impedance, we then can work back-
wards with the junction temperature set to 125°C to see what
maximum ambient air temperature keeps the silicon below
the 125°C temperature.
Procedure:
Place your application into a thermal chamber. You will need
to dissipate enough power in the device so you can obtain a
good thermal impedance value.
Raise the ambient air temperature until the device goes into
thermal shutdown. Record the temperatures of the ambient
air and/or the top case temperature of the LM3410. Calculate
the thermal impedances.
Example from previous calculations (SOT23-5 Package):
P
T
T
A
C
INTERNAL
@ Shutdown = 155°C
@ Shutdown = 159°C
R
V
L
t
I
f
V
RISE
DSON
LED
V
DCR
OUT
SW
I
I
D
η
Q
Q
IN
D
= 107 mW
P
TABLE 2. Power Loss Tabulation
INTERNAL
1.6MHz
225mΩ
75mΩ
16.7V
50mA
0.45V
10nS
10nS
3.3V
3mA
85%
0.82
or the
= P
COND
and
is lower than for
+ P
of a specific application. Be-
value.
P
P
P
SW
P
P
P
P
DIODE
COND
P
LOSS
SWR
OUT
SWF
IND
Q
= 107 mW
and/or
137mW
. However,
23mW
40mW
40mW
10mW
17mW
825W
7mW
. This is
16
Typical LLP & eMSOP typical applications will produce
numbers in the range of 50°C/W to 65°C/W, and
between 18°C/W and 28°C/W. These values are for PCB’s
with two and four layer boards with 0.5 oz copper, and four to
six thermal vias to bottom side ground plane under the DAP.
The thermal impedances calculated above are higher due to
the small amount of power being dissipated within the device.
Note: To use these procedures it is important to dissipate an
amount of power within the device that will indicate a true
thermal impedance value. If one uses a very small internal
dissipated value, one can see that the thermal impedance
calculated is abnormally high, and subject to error. Figure 12
shows the nonlinear relationship of internal power dissipation
vs .
For 5-pin SOT23 package typical applications, R
will range from 80°C/W to 110°C/W, and
50°C/W and 65°C/W. These values are for PCB’s with two &
four layer boards with 0.5 oz copper, with two to four thermal
vias from GND pin to bottom layer.
Here is a good rule of thumb for typical thermal impedances,
and an ambient temperature maximum of 75°C: If your design
requires that you dissipate more than 400mW internal to the
LM3410, or there is 750mW of total power loss in the appli-
cation, it is recommended that you use the 6 pin LLP or the 8
pin eMSOP package with the exposed DAP.
SEPIC Converter
The LM3410 can easily be converted into a SEPIC converter.
A SEPIC converter has the ability to regulate an output volt-
age that is either larger or smaller in magnitude than the input
voltage. Other converters have this ability as well (CUK and
Buck-Boost), but usually create an output voltage that is op-
posite in polarity to the input voltage. This topology is a perfect
fit for Lithium Ion battery applications where the input voltage
for a single cell Li-Ion battery will vary between 2.7V & 4.5V
and the output voltage is somewhere in between. Most of the
SOT23-5 = 93°C/W
SOT23-5 = 56°C/W
.
FIGURE 12. R
θJA
vs Internal Dissipation
will vary between
30038551
θJA
numbers
will vary