- 您現(xiàn)在的位置：買賣IC網 > PDF目錄384596 > LM20144 (National Semiconductor Corporation) 4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator PDF資料下載
參數(shù)資料
| 型號： | LM20144 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| 中文描述： | 第4A，頻率可調的PowerWise㈢同步降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 15/20頁 |
| 文件大小： | 744K |
| 代理商： | LM20144 |
If different start up times are needed the equation shown be-
low can be used to calculate the start up time.
As shown above, the start up time is influenced by the value
of the Soft-Start capacitor C
SS
(F) and the 5 μA Soft-Start pin
current I
(A). that may be found in the electrical character-
istics table.
While the Soft-Start capacitor can be sized to meet many start
up requirements, there are limitations to its size. The Soft-
Start time can never be faster than 1 ms due to the internal
default 1 ms start up time. When the device is enabled there
is an approximate time interval of 50 μs when the Soft-Start
capacitor will be discharged just prior to the Soft-Start ramp.
If the enable pin is rapidly pulsed or the Soft-Start capacitor
is large there may not be enough time for C
to completely
discharge resulting in start up times less than predicted. To
aid in discharging the Soft-Start capacitor during long disable
periods an external 1 M
resistor from SS/TRK to ground can
be used without greatly affecting the start-up time.
USING PRECISION ENABLE AND POWER GOOD
The precision enable (EN) and power good (PGOOD) pins of
the LM20144 can be used to address many sequencing re-
quirements. The turn-on of the LM20144 can be controlled
with the precision enable pin by using two external resistors
as shown in
Figure 6
.
30030626
FIGURE 6. Sequencing LM20144 with Precision Enable
The value for resistor R
can be selected by the user to control
the current through the divider. Typically this resistor will be
selected to be between 10 k
and 1 M
. Once the value for
R
is chosen the resistor R
can be solved using the equation
below to set the desired turn-on voltage.
When designing for a specific turn-on threshold (V
TO
) the tol-
erance on the input supply, enable threshold (V
), and
external resistors needs to be considered to insure proper
turn-on of the device.
The LM20144 features an open drain power good (PGOOD)
pin to sequence external supplies or loads and to provide fault
detection. This pin requires an external resistor (R
) to pull
PGOOD high while when the output is within the PGOOD tol-
erance window. Typical values for this resistor range from 10
k
to 100 k
.
TRACKING AN EXTERNAL SUPPLY
By using a properly chosen resistor divider network connect-
ed to the SS/TRK pin, as shown in
Figure 7
, the output of the
LM20144 can be configured to track an external voltage
source to obtain a simultaneous or ratiometric start up.
30030620
FIGURE 7. Tracking an External Supply
Since the Soft-Start charging current I
is always present on
the SS/TRK pin, the size of R2 should be less than 10 k
to
minimize the errors in the tracking output. Once a value for
R2 is selected the value for R1 can be calculated using ap-
propriate equation in
Figure 8
, to give the desired start up.
Figure 8
shows two common start up sequences; the top
waveform shows a simultaneous start up while the waveform
at the bottom illustrates a ratiometric start up.
30030621
FIGURE 8. Common Start Up Sequences
A simultaneous start up is preferred when powering most FP-
GAs, DSPs, or other microprocessors. In these systems the
higher voltage, V
OUT1
, usually powers the I/O, and the lower
voltage, V
, powers the core. A simultaneous start up pro-
vides a more robust power up for these applications since it
avoids turning on any parasitic conduction paths that may ex-
ist between the core and the I/O pins of the processor.
15
www.national.com
L
相關PDF資料 |
PDF描述 |
|---|---|
| LM20144MH | 4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20144MHE | 4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20144MHX | 4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20145 | 5A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20154 | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator with SYNCOUT |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM20144_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:4A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20144EVAL | 功能描述:電源管理IC開發(fā)工具 LM20144 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM20144MH | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 2.95V to 5.5V 16-Pin TSSOP EP Rail 制造商:Texas Instruments 功能描述:BUCK REG, 4A, SYNC, POWERWISE, TSSOP16 |
| LM20144MH/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM20144MHE | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 2.95V to 5.5V 16-Pin TSSOP EP T/R |
發(fā)布緊急采購，3分鐘左右您將得到回復。