- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄384596 > LM20145 (National Semiconductor Corporation) 5A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator PDF資料下載
參數(shù)資料
| 型號(hào)： | LM20145 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 5A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| 中文描述： | 第5A，頻率可調(diào)的PowerWise㈢同步降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 15/22頁 |
| 文件大?。?/td> | 601K |
| 代理商： | LM20145 |
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 1ms 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 of 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 LM20145 can be used to address many sequencing re-
quirements. The turn-on of the LM20145 can be controlled
with the precision enable pin by using two external resistors
as shown in
Figure 6
.
30030726
FIGURE 6. Sequencing LM20145 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 LM20145 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
LM20145 can be configured to track an external voltage
source to obtain a simultaneous or ratiometric start up.
30030720
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.
30030721
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(guān)PDF資料 |
PDF描述 |
|---|---|
| LM20154 | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator with SYNCOUT |
| LM20154MH | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator with SYNCOUT |
| LM20154MHE | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator with SYNCOUT |
| LM20154MHX | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator with SYNCOUT |
| LM20242 | 36V, 2A PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM20145_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:5A, PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| LM20145CS-A | 制造商:CEC Industries 功能描述:LED, RPL, BULB, AMBER, T-6, E12, Lamp Base Type:Candelabra Screw, LED Color:Ambe |
| LM20145CS-B | 制造商:CEC Industries 功能描述:LED, RPL, BULB, BLUE, T-6, E12; Lamp Base Type:Candelabra Screw; LED Color:Blue; Wavelength Typ:470nm; Power Rating:720mW; Bulb Size:T-6; Supply Voltage:145V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
| LM20145CS-G | 制造商:CEC Industries 功能描述:LED, RPL, BULB, GREEN, T-6, E12; Lamp Base Type:Candelabra Screw; LED Color:Green; Wavelength Typ:525nm; Power Rating:720mW; Bulb Size:T-6; Supply Voltage:145V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
| LM20145CS-R | 制造商:CEC Industries 功能描述:LED, RPL, BULB, RED, T-6, E12; Lamp Base Type:Candelabra Screw; LED Color:Red; Wavelength Typ:629nm; Power Rating:720mW; Bulb Size:T-6; Supply Voltage:145V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。