- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄384595 > LM20123MHE (NATIONAL SEMICONDUCTOR CORP) 3A, 1.5MHz PowerWise㈢ Synchronous Buck Regulator PDF資料下載
參數(shù)資料
| 型號： | LM20123MHE |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3A, 1.5MHz PowerWise㈢ Synchronous Buck Regulator |
| 中文描述： | 5.3 A SWITCHING REGULATOR, 1650 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | TSSOP-16 |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 494K |
| 代理商： | LM20123MHE |
function is set by the feedback resistor ratio, error amp gain,
and external compensation network.
To achieve a -20dB/decade slope, the error amplifier zero,
located at f
, should positioned to cancel the output filter
pole (f
). An additional error amp pole, located at f
,
can be added to cancel the output filter zero at f
. Can-
cellation of the output filter zero is recommended if larger
value, non-ceramic output capacitors are used.
Compensation of the LM20123 is achieved by adding an RC
network as shown in
Figure 5
below.
30030114
FIGURE 5. Compensation Network for LM20123
A good starting value for C
C1
for most applications is 4.7 nF.
Once the value of C
is chosen the value of R
should be
calculated using the equation below to cancel the output filter
pole (f
P(FIL)
) as shown in
Figure 4
.
A higher crossover frequency can be obtained, usually at the
expense of phase margin, by lowering the value of C
C1
and
recalculating the value of R
C1
. Likewise, increasing C
C1
and
recalculating R
will provide additional phase margin at a
lower crossover frequency. As with any attempt to compen-
sate the LM20123 the stability of the system should be verified
for desired transient droop and settling time.
If the output filter zero, f
approaches the crossover fre-
quency (f
), an additional capacitor (C
) should be placed at
the COMP pin to ground. This capacitor adds a pole to cancel
the output filter zero assuring the crossover frequency will
occur before the double pole at f
/2 degrades the phase
margin. The output filter zero is set by the output capacitor
value and ESR as shown in the equation below.
If needed, the value for C
C2
should be calculated using the
equation shown below.
Where R
is the output capacitor series resistance and
R
C1
is the calculated compensation resistance.
AVIN FILTERING COMPONENTS (C
F
and R
F
)
To prevent high frequency noise spikes from disturbing the
sensitive analog circuitry connected to the AVIN and AGND
pins, a high frequency RC filter is required between PVIN and
AVIN. These components are shown in
Figure 2
. as C
and
R
. The required value for R
is 1
. C
must be used. Rec-
ommended value of C
is 1.0 μF. The filter capacitor, C
F
should be placed as close to the IC as possible with a direct
connection from AVIN to AGND. A good quality X5R or X7R
ceramic capacitor should be used for C
F
.
SUB-REGULATOR BYPASS CAPACITOR (C
VCC
)
The capacitor at the VCC pin provides noise filtering and sta-
bility for the internal sub-regulator. The recommended value
of C
should be no smaller than 1 μF and no greater than
10 μF. The capacitor should be a good quality ceramic X5R
or X7R capacitor. In general, a 1 μF ceramic capacitor is rec-
ommended for most applications.
SETTING THE START UP TIME (C
SS
)
The addition of a capacitor connected from the SS pin to
ground sets the time at which the output voltage will reach the
final regulated value. Larger values for C
will result in longer
start up times.
Table 3
, shown below provides a list of soft
start capacitors and the corresponding typical start up times.
TABLE 3. Start Up Times for Different Soft-Start
Capacitors
Start Up Time (ms)
C
SS
(nF)
none
33
68
100
120
1
5
10
15
20
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
(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 LM20123 can be used to address many sequencing re-
quirements. The turn-on of the LM20123 can be controlled
with the precision enable pin by using two external resistors
as shown in
Figure 6
.
www.national.com
14
L
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM20123MHX | 3A, 1.5MHz PowerWise㈢ Synchronous Buck Regulator |
| LM20124 | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
| LM20124MH | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
| LM20124MHE | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
| LM20124MHX | 4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM20123MHE/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)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(fēng)格:SMD/SMT |
| LM20123MHX | 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 |
| LM20123MHX/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)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(fēng)格:SMD/SMT |
| LM20124 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
| LM20124_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:4A, 1MHz PowerWise㈢ Synchronous Buck Regulator |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。