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參數(shù)資料
| 型號： | LM25066APSQE |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | POWER SUPPLY SUPPORT CKT, QCC24 |
| 封裝： | LLP-24 |
| 文件頁數(shù)： | 11/48頁 |
| 文件大?。?/td> | 1658K |
| 代理商： | LM25066APSQE |
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cycles). The MOSFET manufacturer should be consulted for
guidelines.
- R
DS(on) should be sufficiently low such that the power dissi-
pation at maximum load current (I
LIM
2
x R
DS(on)) does not raise
its junction temperature above the manufacturer’s recom-
mendation.
- The gate-to-source voltage provided by the LM25066A can
be as high as 18.8V at turn-on when the output voltage is zero.
At turn-off the reverse gate-to-source voltage will be equal to
the output voltage at the instant the GATE pin is pulled low.
If the device chosen for Q
1 is not rated for these voltages, an
external zener diode must be added from its gate to source,
with the zener voltage less than the device maximum V
GS
rating. The zener diode’s working voltage protects the MOS-
FET during turn-on, and its forward voltage protects the MOS-
FET during shutoff. The zener diode’s forward current rating
must be at least 190 mA to conduct the GATE pull-down cur-
rent when a circuit breaker condition is detected.
CURRENT LIMIT (R
S)
The LM25066A monitors the current in the external MOSFET
Q
1 by measuring the voltage across the sense resistor (RS),
connected from VIN to SENSE. The required resistor value is
calculated from:
(1)
where I
LIM is the desired current limit threshold. If the voltage
across R
S reaches VCL, the current limit circuit modulates the
gate of Q
1 to regulate the current at ILIM. While the current
limiting circuit is active, the fault timer is active as described
in the Fault Timer & Restart section. For proper operation,
R
S must be less than 200 m.
V
CL can be set to either 25mV or 46mV via hardware and/or
software. This setting defaults to use of CL pin which when
grounded is 25mV or high is 46mV. The value when powered
can
be
set
via
the
PMBus
with
the
MFR_SPECIFIC_DEVICE_SETUP command, which de-
faults to the 25mV setting.
Once the desired setting is known, calculate the shunt based
on that input voltage and maximum current. While the maxi-
mum load current in normal operation can be used to deter-
mine the required power rating for resistor R
S, basing it on the
current limit value provides a more reliable design since the
circuit can operate near the current limit threshold continu-
ously. The resistor’s surge capability must also be considered
since the circuit breaker threshold is 1.8 or 3.6 times the cur-
rent limit threshold.
Connections from R
S to the LM25066A should be made using
Kelvin techniques. In the suggested layout of Figure 7, the
small pads at the lower corners of the sense resistor connect
only to the sense resistor terminals and not to the traces car-
rying the high current. With this technique, only the voltage
across the sense resistor is applied to VIN and SENSE, elim-
inating the voltage drop across the high current solder con-
nections.
30146019
FIGURE 7. Sense Resistor Connections
POWER LIMIT THRESHOLD
The LM25066A determines the power dissipation in the ex-
ternal MOSFET (Q
1) by monitoring the drain current (the
current in R
S) and the VDS of Q1 (SENSE to OUT pins). The
resistor at the PWR pin (R
PWR) sets the maximum power dis-
sipation for Q
1 and is calculated from the following equation:
R
PWR = 1.71 x 10
5
x R
S x PMOSFET(LIM)
(2)
where P
MOSFET(LIM) is the desired power limit threshold for
Q
1 and RS is the current sense resistor described in the Cur-
rent Limit section. For example, if R
S is 10 m, and the
desired power limit threshold is 20W, R
PWR calculates to 34.2
k
. If Q
1’s power dissipation reaches the threshold, Q1’s gate
is modulated to regulate the load current, keeping Q
1’s power
from exceeding the threshold. For proper operation of the
power limiting feature, R
PWR must be ≤150 k. While the
power limiting circuit is active, the fault timer is active as de-
scribed in the Fault Timer & Restart section. Typically, power
limit is reached during startup or if the output voltage falls be-
casue of a severe overload or short circuit. The programmed
maximum power dissipation should have a reasonable mar-
gin from the maximum power defined by the SOA chart,
especially if retry is enabled since the MOSFET will be re-
peatedly stressed during fault restart cycles. The MOSFET
manufacturer should be consulted for guidelines. If the appli-
cation does not require use of the power limit function, the
PWR pin can be left open. The accuracy of the power limit
function at turn-on may degrade if a very low value power
dissipation limit is set. The reason for this caution is that the
voltage across the sense resistor, which is monitored and
regulated by the power limit circuit, is lowest at turn-on when
19
www.national.com
LM25066A
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|---|---|
| LM25066APSQE/NOPB | 功能描述:熱插拔功率分布 RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
| LM25066APSQX | 制造商:TI 制造商全稱:Texas Instruments 功能描述:System Power Management and Protection IC with PMBusa?￠ |
| LM25066APSQX/NOPB | 功能描述:熱插拔功率分布 RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
| LM25066EVK/NOPB | 功能描述:電源管理IC開發(fā)工具 LM25066 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓: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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