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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： | 6/20页 |
| 文件大小： | 492K |
| 代理商： | LM20323AMHE |
The value for resistor R
B can be selected by the user to control
the current through the divider. Typically this resistor will be
selected to be between 1 k
and 49.9 k. Once the value for
R
B is chosen the resistor RA 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
IH_EN), and
external resistors need to be considered to ensure proper
turn-on of the device.
The LM20323A 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
PG) to pull
PGOOD high when the output is within the PGOOD tolerance
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 6, the output of the
LM20323A can be configured to track an external voltage
source to obtain a simultaneous or ratiometric start up.
30077261
FIGURE 6. Tracking an External Supply
Since the soft-start charging current I
SS 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 7, to give the desired start up.
Figure 6 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.
30077278
FIGURE 7. 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
OUT2, 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.
The second most common power on behavior is known as a
ratiometric start up. This start up is preferred in applications
where both supplies need to be at the final value at the same
time.
Similar to the soft-start function, the fastest start up possible
is 1ms regardless of the rise time of the tracking voltage.
When using the track feature the final voltage seen by the SS/
TRACK pin should exceed 1V to provide sufficient overdrive
and transient immunity.
BENEFIT OF AN EXTERNAL SCHOTTKY
The LM20323A employs a 40ns dead time between conduc-
tion of the control and synchronous FETs in order to avoid the
situation where both FETs simultaneously conduct, causing
shoot-through current. During the dead time, the body diode
of the synchronous FET acts as a free-wheeling diode and
conducts the inductor current. The structure of the high volt-
age DMOS is optimized for high breakdown voltage, but this
typically leads to inefficient body diode conduction due to the
reverse recovery charge. The loss associated with the re-
verse recovery of the body diode of the synchronous FET
manifests itself as a loss proportional to load current and
switching frequency. The additional efficiency loss becomes
apparent at higher input voltages and switching frequencies.
One simple solution is to use a small 1A external Schottky
diode between SW and GND as shown in Figure 12. The ex-
ternal Schottky diode effectively conducts all inductor current
during the dead time, minimizing the current passing through
www.national.com
14
LM20323A
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PDF描述 |
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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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