参数资料
型号: L5988D
厂商: STMICROELECTRONICS
元件分类: 稳压器
英文描述: 5.6 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封装: LEAD FREE, HTSSOP-16
文件页数: 32/52页
文件大小: 1858K
代理商: L5988D
Application information
L5988D
38/52
Doc ID 15324 Rev 3
The junction temperature TJ can be calculated as:
Where TA is the ambient temperature and PTOT is the sum of the power losses just seen.
RthJA is the equivalent static thermal resistance junction to ambient of the device; it can be
calculated as the parallel of many paths of heat conduction from the junction to the ambient.
For this device the path through the exposed pad is the one conducting the largest amount
of heat. The static RthJA measured on the application is about 40 °/W.
The thermal impedance of the system, considered as the device in HTSSOP16 package
soldered on the application board, takes on an important rule when the maximum output
power is limited by the static thermal performance and not by the electrical performance of
the device. Therefore the embedded power elements could manage an higher current but
the system is already taking away the maximum power generated by the internal losses.
In case the output power increases the thermal shutdown will be triggered because the
junction temperature triggers the designed thermal shutdown threshold.
The RTH is a static parameter of the package: it sets the maximum power loss which can be
generated from the system given the operation conditions.
If we suppose, as an example, TA = 40 °C, 140 °C is the maximum operating temperature
before triggering the thermal shutdown and RTH = 40 °C/W so the maximum power loss
achievable with the thermal performance of the system will be:
The switching, conduction and quiescent losses in case of VIN = 12 V, VOUT = 1.2 V, fSW =
400 kHz are plotted in Figure 21. The calculations are performed considering the typical
RDS(on) of the power element for a junction temperature of 125 °C (RDS_ON HS = 120 mΩ,
RDS_ON LS = 83 mΩ; see Maximum ratings on page 8 for details).
Figure 21.
Estimation of the internal power losses (VIN = 12 V, VOUT = 1.2 V,
fSW = 400 kHz)
T
J
T
A
Rth
JA
P
TOT
+
=
P
MAX DC
ΔT
R
TH
-----------
T
J MAX
T
AMB
R
TH
--------------------------------------
100
40
----------
2.5W
==
=
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