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TJ2996DP 参数 Datasheet PDF下载

TJ2996DP图片预览
型号: TJ2996DP
PDF下载: 下载PDF文件 查看货源
内容描述: DDR终端稳压器 [DDR Termination Regulator]
分类和应用: 稳压器双倍数据速率
文件页数/大小: 14 页 / 973 K
品牌: HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
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DDR Termination Regulator
TJ2996
under all conditions. The reason for this is the standard packages are not able to thermally dissipate the
heat as a result of the internal power loss. If large currents are required for longer durations, then care
should be taken to ensure that the maximum junction temperature is not exceeded. Proper thermal
derating should always be used (please refer to the Thermal Dissipation section). If the junction
temperature exceeds the thermal shutdown point than
V
TT
will tri-state until the part returns below the
hysteretic trip-point.
THERMAL DISSIPATION
Since the TJ2996
is a linear regulator any current flow from V
TT
will result in internal power dissipation
generating heat. To prevent damaging the part from exceeding the maximum allowable junction
temperature, care should be taken to derate the part dependent on the maximum expected ambient
temperature and power dissipation. The maximum allowable internal temperature rise, T
Rmax
can be
calculated given the maximum ambient temperature, T
Amax
of the application and the maximum allowable
junction temperature, T
Jmax
.
T
Rmax
= T
Jmax
T
Amax
From this equation, the maximum allowable power dissipation, P
Dmax
of the part can be
calculated:
P
Dmax
= T
Rmax
/
θ
JA
The maximum allowable value for junction-to-ambient thermal resistance,
θ
JA
, can be calculated using
the formula:
θ
JA
= T
Rmax
/ P
D
= (T
Jmax
– T
Amax
) / P
D
The
θ
JA
of the TJ2996 will be dependent on several variables: the package used; the thickness of
copper; the number of vias and the airflow. For instance, the
θ
JA
of the SOP8 is 165°C/W with the
package mounted to a standard 8x4 2-layer board with 1oz. copper, no airflow, and 0.5W dissipation at
room temperature. This value can be reduced to 152°C/W by changing to a 3x4 board with 2 oz. copper
that is the JEDEC standard.
Additional improvements can be made by the judicious use of vias to connect the part and
dissipate heat to an internal ground plane. Using larger traces and more copper on the top side of
the board can also help.
With careful layout it is possible to reduce the
θ
JA
further than the nominal
values. Additional improvements in lowering the
θ
JA
can also be achieved with a constant airflow
across the package.
Optimizing the
θ
JA
and placing the TJ2996 in a section of a board exposed to lower ambient
temperature allows the part to operate with higher power dissipation. The internal power dissipation
can be calculated by summing the three main sources of loss: output current at V
TT
, either sinking or
sourcing, and quiescent current at AVIN and V
DDQ
. During the active state (when shutdown is not held
low) the total internal power dissipation can be calculated from the following equations:
Jul. 2010 - Rev. 1.5.3
8/14
HTC