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参数资料
| 型号： | LM25066APSQE |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 电源管理 |
| 英文描述： | POWER SUPPLY SUPPORT CKT, QCC24 |
| 封装： | LLP-24 |
| 文件页数： | 13/48页 |
| 文件大小： | 1658K |
| 代理商： | LM25066APSQE |
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the regulated current is at a minimum. The voltage across the
sense resistor during power limit can be expressed as follows:
(3)
where I
L is the current in RS, and VDS is the voltage across
Q
1. For example, if the power limit is set at 20W with RS = 10
m
and V
DS = 15V, the sense resistor voltage calculates to
13.3 mV, which is comfortably regulated by the LM25066A.
However, if the power limit is set lower (e.g. 2W), the sense
resistor voltage calculates to 1.33 mV. At this low level, noise
and offsets within the LM25066A may degrade the power limit
accuracy. To maintain accuracy, the sense resistor voltage
should not be less than 5 mV.
TURN-ON TIME
The output turn-on time depends on whether the LM25066A
operates in current limit, or in both power limit and current
limit, during turn-on.
A) Turn-on with current limit only:
The current limit thresh-
old (I
LIM) is determined by the current sense resistor (RS). If
the current limit threshold is less than the current defined by
the power limit threshold at maximum V
DS, the circuit operates
at the current limit threshold only during turn-on. Referring to
Figure 8A, as the load current reaches I
LIM, the gate-to-source
voltage is controlled at V
GSL to maintain the current at ILIM. As
the output voltage reaches its final value (V
DS 0V) the drain
current reduces to its normal operating value. The time for the
OUT pin voltage to transition from zero volts to V
SYS is equal
to:
(4)
where C
L is the load capacitance. For example, if VSYS = 12V,
C
L = 1000 F, and ILIM = 1A, tON calculates to 12 ms. The
maximum instantaneous power dissipated in the MOSFET is
12W. This calculation assumes the time from t
9(a) is small compared to t
ON, and the load does not draw any
current until after the output voltage has reached its final val-
ue, and PGD switches high (Figure 8A). The Fault Timeout
Period must be set longer than t
ON to prevent a fault shutdown
before the turn-on sequence is complete.
If the load draws current during the turn-on sequence (Figure
8B), the turn-on time is longer than the above calculation and
is approximately equal to:
(5)
where R
L is the load resistance. The Fault Timeout Period
must be set longer than t
ON to prevent a fault shutdown before
the turn-on sequence is complete.
30146022
A. No Load Current During Turn-On
30146023
B. Load Draws Current During Turn-On
FIGURE 8.
B) Turn-On with Power Limit and Current Limit:
The max-
imum allowed power dissipation in Q
1 (PMOSFET(LIM)) is de-
fined by the resistor at the PWR pin and the current sense
resistor R
S. See the Power Limit Threshold section. If the cur-
rent limit threshold (I
LIM) is higher than the current defined by
the power limit threshold at maximum V
DS (PMOSFET(LIM)/
V
SYS), the circuit operates initially in the power limit mode
when the V
DS of Q1 is high and then transitions to current limit
mode as the current increases to I
LIM and VDS decreases. As-
suming the load (R
L) is not connected during turn-on, the time
for the output voltage to reach its final value is approximately
equal to:
(6)
For example, if V
SYS = 12V, CL = 1000 F, ILIM = 1A, and
P
MOSFET(LIM) = 10W, tON calculates to 12.2 ms, and the initial
current level (I
P) is approximately 0.83A. The Fault Timeout
Period must be set longer than t
ON.
www.national.com
20
LM25066A
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM25066APSQE/NOPB | 功能描述:热插拔功率分布 RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
| LM25066APSQX | 制造商:TI 制造商全称:Texas Instruments 功能描述:System Power Management and Protection IC with PMBusa?￠ |
| LM25066APSQX/NOPB | 功能描述:热插拔功率分布 RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
| LM25066EVK/NOPB | 功能描述:电源管理IC开发工具 LM25066 EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM25066IAPSQ/NOPB | 制造商:Texas Instruments 功能描述:IC PWR MGMT/PROT PMBUS 24WQFN 制造商:Texas Instruments 功能描述:System PWR Mgmt & Protection IC |
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