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| 型号： | LMZ12002EXTTZX |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PSSO7 |
| 封装： | 10.16 X 13.77 MM, 4.57 MM HEIGHT, ROHS COMPLIANT, TO-PMOD, 7 PIN |
| 文件页数： | 6/20页 |
| 文件大小： | 3951K |
| 代理商： | LMZ12002EXTTZX |
PC BOARD LAYOUT GUIDELINES
PC board layout is an important part of DC-DC converter de-
sign. Poor board layout can disrupt the performance of a DC-
DC converter and surrounding circuitry by contributing to EMI,
ground bounce and resistive voltage drop in the traces. These
can send erroneous signals to the DC-DC converter resulting
in poor regulation or instability. Good layout can be imple-
mented by following a few simple design rules.
30117411
1. Minimize area of switched current loops.
From an EMI reduction standpoint, it is imperative to minimize
the high di/dt current paths during PC board layout. The high
current loops that do not overlap have high di/dt content that
will cause observable high frequency noise on the output pin
if the input capacitor C
IN1 is placed a distance away for the
LMZ12002EXT. Therefore physically place C
IN1 asa close as
possible to the LMZ12002EXT VIN and GND exposed pad.
This will minimize the high di/dt area and reduce radiated EMI.
Additionally, grounding for both the input and output capacitor
should consist of a localized top side plane that connects to
the GND exposed pad (EP).
2. Have a single point ground.
The ground connections for the feedback, soft-start, and en-
able components should be routed to the GND pin of the
device. This prevents any switched or load currents from
flowing in the analog ground traces. If not properly handled,
poor grounding can result in degraded load regulation or er-
ratic output voltage ripple behavior. Provide the single point
ground connection from pin 4 to EP.
3. Minimize trace length to the FB pin.
Both feedback resistors, R
FBT and RFBB, and the feed forward
capacitor C
FF, should be located close to the FB pin. Since
the FB node is high impedance, maintain the copper area as
small as possible. The trace are from R
FBT, RFBB, and CFF
should be routed away from the body of the LMZ12002EXT
to minimize noise.
4. Make input and output bus connections as wide as
possible.
This reduces any voltage drops on the input or output of the
converter and maximizes efficiency. To optimize voltage ac-
curacy at the load, ensure that a separate feedback voltage
sense trace is made to the load. Doing so will correct for volt-
age drops and provide optimum output accuracy.
5. Provide adequate device heat-sinking.
Use an array of heat-sinking vias to connect the exposed pad
to the ground plane on the bottom PCB layer. If the PCB has
a plurality of copper layers, these thermal vias can also be
employed to make connection to inner layer heat-spreading
ground planes. For best results use a 6 x 6 via array with
minimum via diameter of 10mils (254
μm) thermal vias spaced
59mils (1.5 mm). Ensure enough copper area is used for heat-
sinking to keep the junction temperature below 125°C.
Additional Features
OUTPUT OVER-VOLTAGE COMPARATOR
The voltage at FB is compared to a 0.92V internal reference.
If FB rises above 0.92V the on-time is immediately terminat-
ed. This condition is known as over-voltage protection (OVP).
It can occur if the input voltage is increased very suddenly or
if the output load is decreased very suddenly. Once OVP is
activated, the top MOSFET on-times will be inhibited until the
condition clears. Additionally, the synchronous MOSFET will
remain on until inductor current falls to zero.
CURRENT LIMIT
Current limit detection is carried out during the off-time by
monitoring the current in the synchronous MOSFET. Refer-
ring to the Functional Block Diagram, when the top MOSFET
is turned off, the inductor current flows through the load, the
PGND pin and the internal synchronous MOSFET. If this cur-
rent exceeds 2.85A (typical) the current limit comparator dis-
ables the start of the next on-time period. The next switching
cycle will occur only if the FB input is less than 0.8V and the
inductor current has decreased below 2.85A. Inductor current
is monitored during the period of time the synchronous MOS-
FET is conducting. So long as inductor current exceeds
2.85A, further on-time intervals for the top MOSFET will not
occur. Switching frequency is lower during current limit due to
the longer off-time. It should also be noted that current limit is
dependent on both duty cycle and temperature as illustrated
in the graphs in the typical performance section.
THERMAL PROTECTION
The junction temperature of the LMZ12002EXT should not be
allowed to exceed its maximum ratings. Thermal protection is
implemented by an internal Thermal Shutdown circuit which
activates at 165 °C (typ) causing the device to enter a low
power standby state. In this state the main MOSFET remains
off causing V
O to fall, and additionally the CSS capacitor is
discharged to ground. Thermal protection helps prevent
catastrophic failures for accidental device overheating. When
the junction temperature falls back below 145 °C (typ Hyst =
20 °C) the SS pin is released, V
O rises smoothly, and normal
operation resumes.
Applications requiring maximum output current especially
those at high input voltage may require application derating
at elevated temperatures.
ZERO COIL CURRENT DETECTION
The current of the lower (synchronous) MOSFET is monitored
by a zero coil current detection circuit which inhibits the syn-
chronous MOSFET when its current reaches zero until the
next on-time. This circuit enables the DCM operating mode,
which improves efficiency at light loads.
www.national.com
14
LMZ12002EXT
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LMZ12002EXTTZX/NOPB | 功能描述:DC/DC转换器 RoHS:否 制造商:Murata 产品: 输出功率: 输入电压范围:3.6 V to 5.5 V 输入电压（标称）: 输出端数量:1 输出电压（通道 1）:3.3 V 输出电流（通道 1）:600 mA 输出电压（通道 2）: 输出电流（通道 2）: 安装风格:SMD/SMT 封装 / 箱体尺寸: |
| LMZ12002TZ-ADJ | 制造商:NSC 制造商全称:National Semiconductor 功能描述:2A SIMPLE SWITCHER? Power Module with 20V Maximum Input Voltage |
| LMZ12002TZ-ADJ/NOPB | 功能描述:DC/DC转换器 12V,2A PWR MODULE RoHS:否 制造商:Murata 产品: 输出功率: 输入电压范围:3.6 V to 5.5 V 输入电压（标称）: 输出端数量:1 输出电压（通道 1）:3.3 V 输出电流（通道 1）:600 mA 输出电压（通道 2）: 输出电流（通道 2）: 安装风格:SMD/SMT 封装 / 箱体尺寸: |
| LMZ12002TZADJNOPB | 制造商:Texas Instruments 功能描述:Module DC-DC 1-OUT 0.8V to 6V 2A 7-Pin TO-PMOD EP |
| LMZ12002TZE-ADJ | 制造商:NSC 制造商全称:National Semiconductor 功能描述:2A SIMPLE SWITCHER? Power Module with 20V Maximum Input Voltage |
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