參數(shù)資料
型號(hào)： LM20242
廠商： National Semiconductor Corporation
英文描述： 36V, 2A PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator
中文描述： 至36V，2A條的PowerWise㈢可調(diào)頻率同步降壓穩(wěn)壓器
文件頁(yè)數(shù)： 13/20頁(yè)
文件大?。?/td> 384K
代理商： LM20242
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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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM20242_08 制造商:NSC 制造商全稱:National Semiconductor 功能描述:36V, 2A PowerWise㈢ Adjustable Frequency Synchronous Buck Regulator
LM20242EVAL 功能描述:BOARD EVAL 2A POWERWISE LM20242 RoHS:否 類別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)估板 - DC/DC 與 AC/DC（離線）SMPS 系列:PowerWise® 產(chǎn)品培訓(xùn)模塊:Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):升壓 頻率 - 開(kāi)關(guān):3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969
LM20242EVAL/NOPB 功能描述:電源管理IC開(kāi)發(fā)工具 LM20242 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V
LM20242MH 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP Rail 制造商:Texas Instruments 功能描述:SWITCH REG, 36V, 2A, TSSOP20, POWERWISE 制造商:Texas Instruments 功能描述:SWITCH REG, 36V, 2A, TSSOP20, POWERWISE; Primary Input Voltage:36V; No. of Outputs:1; Output Voltage:32V; Output Current:2A; Voltage Regulator Case Style:TSSOP; No. of Pins:20; Operating Temperature Min:-40C; Operating Temperature ;RoHS Compliant: Yes
LM20242MH/NOPB 功能描述:直流/直流開(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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
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