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LM3554TMX/NOPB датащи(PDF) 35 Page - Texas Instruments

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номер детали LM3554TMX/NOPB
подробное описание детали  Synchronous Boost Converter
PDF  47 Pages
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производитель  TI1 [Texas Instruments]
домашняя страница  http://www.ti.com
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LM3554TMX/NOPB датащи(HTML) 35 Page - Texas Instruments

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J
T
0.93W
75.8 C/W + 25 C = 95.5 C
u
q
q
q
mW
930
=
mW
14
+
mW
420
+
mW
357
+
mW
139
=
PDISS
]
2
LED
1
LED
LED
I
+
I
=
I
IND
LED
LOAD
I
+
I
=
I
)
IND
I
x
IND
- V
LOAD
PFET
I
x
- R
(
IN
V
LED +
I
x
)
LED
- V
LOAD
I
x
PFET
- R
(
IN
V
[
PFET
2
LOAD
DISS
+
R
x
I
=
P
2
LED
1
LED
LED
I
+
I
=
I
LOAD =
I
IND
LED
I
+
I
I
x
IND
)
- V
IND
R
x
PFET
I
x
2
LOAD
+
R
x
NFET
I
x
2
LOAD
¹
·
) x
+ 0.3V - V
IN
=
P
DISS
(V
LED
©
§
+ 0.3V
V
LED
)
V
2
IN
VLED + 0.3V
V
IN
¹
·
©
§
(
+
I
+ 0.3V x
LED
VLED + 0.3V
35
LM3554
www.ti.com
SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016
Product Folder Links: LM3554
Submit Documentation Feedback
Copyright © 2009–2016, Texas Instruments Incorporated
(12)
8.2.2.7.3
LED Pass Mode
In LED mode with VIN – ILOAD × RPFET > VLED + 0.3 V, the LM3554 operates in pass mode. In this case, the NFET
is off, and the PFET is fully on. The difference between VIN - ILOAD × RPMOS and VLED are dropped across the
current sources. In this situation the total power dissipated in the LM3554 is approximated as:
(13)
Once the total power dissipated in the LM3554 is calculated the ambient temperature and the thermal resistance
of the 16-pin DSBGA (YFQ package) are used to calculate the total die temperature (or junction temperature TJ).
As an example, assume the LM3554 is operating at VIN = 3.6 V and configured for voltage-output mode with
VOUT = 5 V and IOUT = 0.7 A. The LED currents are then programmed in torch mode with 150 mA each at VLED =
3.6 V. Additionally, the indicator LED has 10 mA at VIND = 3.6 V. Using Equation 12 and Equation 13 above, the
approximate total power dissipated in the device is:
(14)
The die temperature approximation is:
(15)
In this case the device can operate at these conditions. If then the ambient temperature is increased to 85°C, the
die temperature would be 140.8°C; thus, the die temperature would be above the absolute maximum ratings, and
the load current would need to be scaled back. This example demonstrates the steps required to estimate the
amount of current derating based upon operating mode, circuit parameters, and the device's junction-to-ambient
thermal resistance. In this example a thermal resistance of 75.8°C/W was used (JESD51-7 standard). Because
thermal resistance from junction-to-ambient is largely PCB layout dependent, the actual number used likely may
be different and must be taken into account when performing these calculations.



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