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參數資料
| 型號： | LM5642MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩壓器 |
| 英文描述： | High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization |
| 中文描述： | DUAL SWITCHING CONTROLLER, 226 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數： | 14/24頁 |
| 文件大小： | 667K |
| 代理商： | LM5642MTC |
Operating Descriptions
SOFT START
The ON/SS1 pin has dual functionality as both channel
enable and soft start control. Referring to the soft start block
diagram is shown in
Figure 3
, the LM5642 will remain shut-
down mode while both soft start pins are grounded.
The LM5642 will remain in shutdown mode while both soft
start pins are grounded. In a normal application (with a soft
start capacitor connected between the ON/SS1 pin and
SGND) soft start functions as follows. As the input voltage
rises (note: Iss starts to flow when VIN
≥
2.2V), the internal
5V LDO starts up, and an internal 2.4μA current charges the
soft start capacitor. During soft start, the error amplifier out-
put voltage at the COMPx pin is clamped at 0.55V and the
duty cycle is controlled only by the soft start voltage. As the
SSx pin voltage ramps up, the duty cycle increases propor-
tional to the soft start ramp, causing the output voltage to
ramp up. The rate at which the duty cycle increases depends
on the capacitance of the soft start capacitor. The higher the
capacitance, the slower the output voltage ramps up. When
the corresponding output voltage exceeds 98% (typical) of
the set target voltage, the regulator switches from soft start
to normal operating mode. At this time, the 0.55V clamp at
the output of the error amplifier releases and peak current
feedback control takes over. Once in peak current feedback
control mode, the output of the error amplifier will travel
within the 0.5V and 2V window to achieve PWM control. See
Figure 4
.
The amount of capacitance needed for a desired soft-start
time can be approximated in the following equation:
(1)
In this equation I
= 2.4μA for one channel and 4.8μA if the
channels are paralleled. t
ss
is the desired soft-start time.
Finally,
(2)
During soft start, over-voltage protection and current limit
remain in effect. The under voltage protection feature is
activated when the ON/SS pin exceeds the timeout thresh-
old (3.4V typical). If the ON/SSx capacitor is too small, the
duty cycle may increase too rapidly, causing the device to
latch off due to output voltage overshoot above the OVP
threshold. This becomes more likely in applications requiring
low output voltage, high input voltage and light load. A
capacitance of 10nF is recommended at each soft start pin
to provide a smooth monotonic output ramp.
OVER VOLTAGE PROTECTION (OVP)
If the output voltage on either channel rises above 113% of
nominal, over voltage protection activates. Both channels
will latch off. When the OVP latch is set, the high side FET
driver, HDRVx, is immediately turned off and the low side
FET driver, LDRVx, is turned on to discharge the output
20060106
FIGURE 3. Soft-Start and ON/OFF
20060107
FIGURE 4. Voltage Clamp at COMPx Pin
20060108
FIGURE 5. OVP and UVP
L
www.national.com
14
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM5642MTC/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642MTCX | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642MTCX/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642XMH | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642XMH/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
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