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參數(shù)資料
| 型號： | LP2994MX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 通用總線功能 |
| 英文描述： | DDR Termination Regulator |
| 中文描述： | BUS TERMINATOR SUPPORT CIRCUIT, PDSO8 |
| 封裝： | SOP-8 |
| 文件頁數(shù)： | 9/15頁 |
| 文件大?。?/td> | 257K |
| 代理商： | LP2994MX |
Component Selection
(Continued)
dielectric types have poor capacitance characteristics as a
function of voltage and temperature. Because of the typically
low value of capacitance it is recommended to use ceramic
capacitors in parallel with another capacitor such as an
aluminum electrolytic. A dielectric of X5R or better is recom-
mended for all ceramic capacitors.
Hybrid - Several hybrid capacitors such as OS-CON and SP
are available from several manufacturers. These offer a
large capacitance while maintaining a low ESR. These are
the best solution when size and performance are critical,
although their cost is typically higher than other capacitors.
Thermal Dissipation
Since the LP2994 is a linear regulator any current flow from
V
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 ambi-
ent temperature and power dissipation. The maximum allow-
able 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 power dissipation (P
D
) of
the part can be calculated:
P
Dmax
= T
Rmax
/
θ
JA
The
θ
of the LP2994 will be dependent on several vari-
ables: the package used; the thickness of copper; the num-
ber of vias and the airflow. For instance, the
θ
of the SO-8
is 163C/W with the package mounted to a standard 8x4
2-layer board with 1oz. copper, no airflow, and 0.5W dissi-
pation at room temperature. This value can be reduced to
151.2C/W by changing to a 3x4 board with 2 oz. copper that
is the JEDEC standard. Figure 3 shows how the
θ
JA
varies
with airflow for the two boards mentioned.
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
shown in Figure 3
Optimizing the
θ
and placing the LP2994 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
, either sinking or
sourcing, and quiescent current at AVIN and V
. During
the active state (when Shutdown is not held low) the total
internal power dissipation can be calculated from the follow-
ing equations:
P
D
= P
AVIN
+ P
VDDQ
+ P
VTT
where,
P
AVIN
= I
AVIN
x V
AVIN
P
VDDQ
= V
VDDQ
x I
VDDQ
= V
VDDQ2
x R
VDDQ
To calculate the maximum power dissipation at V
, both
sinking and sourcing current conditions at V
TT
need to be
examined. Although only one equation will add into the total,
V
TT
cannot source and sink current simultaneously.
P
VTT
= V
VTT
x I
LOAD
(Sinking)
or
P
VTT
= ( V
PVIN
- V
VTT
) x I
LOAD
(Sourcing)
The power dissipation of the LP2994 can also be calculated
during the shutdown state. During this condition the output
V
will tri-state, therefore that term in the power equation
will disappear as it cannot sink or source any current (leak-
age is negligible). The only losses during shutdown will be
the reduced quiescent current at AVIN and the constant
impedance that is seen at the V
DDQ
pin.
P
D
= P
AVIN
+ P
VDDQ
Where,
P
AVIN
= I
AVIN
x V
AVIN
P
VDDQ
= V
VDDQ
x I
VDDQ
= V
VDDQ2
x R
VDDQ
20045928
FIGURE 3.
θ
JA
vs Airflow
L
www.national.com
9
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PDF描述 |
|---|---|
| LP2995LQX | DDR Termination Regulator |
| LP2995MX | DDR Termination Regulator |
| LP2995MR | DDR Termination Regulator |
| LP2995M | DDR Termination Regulator |
| LP2995LQ | DDR Termination Regulator |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LP2994MX/NOPB | 功能描述:IC REGULATOR DDR TERM 8-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 專用型 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,000 系列:- 應(yīng)用:電源，ICERA E400，E450 輸入電壓:4.1 V ~ 5.5 V 輸出數(shù):10 輸出電壓:可編程 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:42-WFBGA，WLCSP 供應(yīng)商設(shè)備封裝:42-WLP 包裝:帶卷 (TR) |
| LP2995LQ | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LP2995LQ/7002047 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LP2995LQ/J7002047 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LP2995LQ/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動電壓（最大值）:307 mV 輸出電流:1 A 負載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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