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參數(shù)資料
| 型號： | LM20242MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 36V, 2A PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator |
| 中文描述： | 4.65 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | TSSOP-20 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大?。?/td> | 384K |
| 代理商： | LM20242MHX |
30031472
FIGURE 4. LM20242 Loop Compensation
The power stage transfer function is dictated by the modula-
tor, output LC filter, and load; while the feedback transfer
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
Z(EA)
, should be positioned to cancel the output fil-
ter pole (f
). An additional error amp pole, located at f
P2
, can be added to cancel the output filter zero at f
.
Cancellation of the output filter zero is recommended if larger
value, non-ceramic output capacitors are used.
Compensation of the LM20242 is achieved by adding an RC
network as shown in
Figure 5
below.
30031445
FIGURE 5. Compensation Network for LM20242
A good starting value for C
for most applications is 4.7 nF.
Once the value of C
C1
is chosen the value of RC 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
. Likewise, increasing C
and
recalculating R
will provide additional phase margin at a
lower crossover frequency. As with any attempt to compen-
sate the LM20242 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.
BOOT CAPACITOR (C
BOOT
)
The LM20242 integrates an N-Channel buck switch and as-
sociated floating high voltage level shift / gate driver. This gate
driver circuit works in conjunction with an internal diode and
an external bootstrap capacitor. A 0.1 μF ceramic capacitor,
connected with short traces between the BOOT pin and SW
pin, is recommended. During the off-time of the buck switch,
the SW pin voltage is approximately 0V and the bootstrap ca-
pacitor is charged from VCC through the internal bootstrap
diode.
SUB-REGULATOR BYPASS CAPACITOR (C
VCC
)
The capacitor at the VCC pin provides noise filtering for the
internal sub-regulator. The recommended value of C
should be no smaller than 0.1 μF and no greater than 1 μF.
The capacitor should be a good quality ceramic X5R or X7R
capacitor. In general, a 1 μF ceramic capacitor is recom-
mended for most applications. The VCC regulator should not
be used for other functions since it isn't protected against
short circuit.
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 2. 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
13
www.national.com
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| LM20242MHX/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 |
| LM2024CS-A | 制造商:CEC Industries 功能描述:LED, RPL, BULB, AMBER, T-6, E12; Lamp Base Type:Candelabra Screw; LED Color:Amber; Wavelength Typ:590nm; Power Rating:720mW; Bulb Size:T-6; Supply Voltage:24V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
| LM2024CS-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:24V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
| LM2024CS-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:24V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
| LM2024CS-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:24V; Current Rating:30mA; Average Bulb Life:100000h; Beam Divergence:360 ;RoHS Compliant: No |
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