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参数资料
| 型号： | LM20323AMHE |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 6 A SWITCHING REGULATOR, 570 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | TSSOP-20 |
| 文件页数： | 5/20页 |
| 文件大小： | 492K |
| 代理商： | LM20323AMHE |
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
P(FIL)).
Compensation of the LM20323A is achieved by adding an RC
network as shown in Figure 4 below.
30077245
FIGURE 4. Compensation Network for LM20323A
A good starting value for C
C1 for most applications is 2.2 nF.
Once the value of C
C1 is chosen the value of RC1 should be
approximated using the equation below to cancel the output
filter pole (f
P(FIL)) as shown in Figure 3.
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 CC1 and
recalculating R
C1 will provide additional phase margin at a
lower crossover frequency. As with any attempt to compen-
sate the LM20323A the stability of the system should be
verified for desired transient droop and settling time.
For low duty cycle operation, when the on-time of the switch
node is less than 200ns, an additional capacitor (C
C2) should
be added from the COMP pin to AGND. The recommended
value of this capacitor is 20pF. If low duty cycle jitter on the
switch node is observed, the value of this capacitor can be
increased to improve noise immunity; however, values much
larger than 100pF will cause the pole f
P2(EA) to move to a lower
frequency degrading the loop stability.
BOOT CAPACITOR (C
BOOT)
The LM20323A 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 F 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
VCC
should be no smaller than 0.1 F and no greater than 1 F.
The capacitor should be a good quality ceramic X5R or X7R
capacitor. In general, a 1 F 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
SS 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)
1
none
5
33
10
68
15
100
20
120
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 and the 4.5 A soft-start pin
current I
SS.
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 s when the soft-start capac-
itor 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
SS to completely discharge
resulting in start up times less than predicted. To aid in dis-
charging of soft-start capacitor during long disable periods an
external 1M
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 LM20323A can be used to address many sequencing re-
quirements. The turn-on of the LM20323A can be controlled
with the precision enable pin by using two external resistors
as shown in Figure 5 .
30077262
FIGURE 5. Sequencing LM20323A with Precision Enable
13
www.national.com
LM20323A
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM20323AMHX | 制造商:NSC 制造商全称:National Semiconductor 功能描述:36V, 3A 500 kHz Synchronous Buck Regulator |
| LM20323EVAL | 功能描述:电源管理IC开发工具 LM20323 EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM20323MH | 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:BUCK REG, 3A, 4V/36V, POWERWISE, 20TSSOP 制造商:Texas Instruments 功能描述:IC, DC-DC CONV; Primary Input Voltage:36V; No. of Outputs:1; Output Voltage:32V; Output Current:3A; No. of Pins:20; Operating Temperature Min:-40C; Operating Temperature Max:125C; Operating Temperature Range:-40C to +125C ;RoHS Compliant: Yes |
| LM20323MH/NOPB | 功能描述:直流/直流开关转换器 36V,3A 500 KHZ SYNC BUCK REG RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM20323MHE | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 36V 20-Pin TSSOP EP T/R |
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