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參數(shù)資料
| 型號： | LM27402SQX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 1350 kHz SWITCHING FREQ-MAX, QCC16 |
| 封裝： | 4 X 4 MM, 0.80 MM HEIGHT, 0.65 MM PITCH, LLP-16 |
| 文件頁數(shù)： | 3/32頁 |
| 文件大?。?/td> | 653K |
| 代理商： | LM27402SQX |
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Theory of Operation
GENERAL INFORMATION
The LM27402 is a single-phase synchronous voltage mode
DC/DC buck controller. The inductor DCR sense capability
and integrated low impedance gate drivers allow the
LM27402 to be used in high current, high power density ap-
plications. Multiple fault conditions are supported including
over-voltage, under-voltage, over-temperature, and over-cur-
rent. The switching frequency can be adjusted over a wide
range either by connecting a clock signal to SYNC pin or a
resistor from FADJ to GND. The LM27402 supports pre-bi-
ased outputs while maintaining synchronous mode operation.
Input voltage feed-forward is incorporated into the control
loop to mitigate the effects of input voltage variation.
UVLO
An under-voltage lockout is built into the LM27402 which al-
lows the device to only switch if the input voltage (VIN) and
the internal sub-regulated voltage (VDD) both exceed 2.9V.
A 300mV UVLO hysteresis exists on both VDD and VIN to
prevent power on and off anomalies related to input voltage
deviations.
PRECISION ENABLE (EN)
The enable pin of the LM27402 allows the output to be toggled
on and off and is a precision analog input. When the EN volt-
age exceeds 1.17V, the controller will initiate the soft-start
sequence as long as the input voltage and sub-regulated volt-
age have exceeded their UVLO thresholds of 2.9V. The EN
pin has an absolute maximum voltage rating of 6.0V and
should not exceed the voltage on VDD. There is an internal 2
A pull-up current source connected to the EN pin. If EN is
open, the LM27402 will turn on automatically if VIN and VDD
exceed 2.9V. If the EN voltage is held below 0.8V, the
LM27402 enters a deep shutdown state where the internal
bias circuitry is off. The quiescent current is approximately 35
A in deep shutdown. The EN pin has 100mV of hysteresis
to reject noise and allow the pin to be resistively coupled to
the input voltage or sequenced with other rails.
SOFT-START AND VOLTAGE TRACKING (SS/TRACK)
When the enable pin has exceeded 1.17V and both VIN and
VDD have exceeded their UVLO thresholds, the LM27402 will
begin charging the output linearly to the voltage level dictated
by the feedback resistor network. The soft-start time is set by
connecting a capacitor from SS/TRACK to GND. After EN
exceeds 1.17V, an internal 3 A current source begins to lin-
early charge the soft-start capacitor. Soft-start allows the user
to limit inrush currents related to high output capacitance and
output slew rate. If a soft-start capacitor is not used, the
LM27402 defaults to a 1.28 ms digitally controlled startup
time. The SS/TRACK pin can also be used to ratiometrically
or coincidentally track an external voltage source. See the
SETTING THE SOFT-START TIME and TRACKING sections
of the design guide for more information.
PRE-BIAS STARTUP
In certain applications, the output may acquire a pre-bias volt-
age before the LM27402 is powered on or enabled. Pre-
biased conditions are managed by preventing switching until
the soft-start (SS/TRACK) voltage exceeds the feedback (FB)
voltage. Once V
SS/TRACK has exceeded VFB, the LM27402 will
begin to switch synchronously and regulate the output volt-
age.
30092645
FIGURE 1. Pre-Bias Startup
Prohibiting switching during a pre-biased startup condition
prevents the output from forcing parasitic paths to conduct
excessive current. The LM27402 will not switch if the output
is pre-biased to a voltage higher than the nominally set output
voltage.
CURRENT LIMIT
The LM27402 may enter two states when a current limit event
is detected. If a current limit condition has occurred, the high-
side FET is immediately turned off until the next switching
cycle. This is considered the first current limit state and pro-
vides an immediate response to any current limit event. Dur-
ing the first state, an internal counter will begin to record the
number of over-current events. The counter is reset if 32 con-
secutive switching cycles occur with no current limit events
detected. If five over-current events are detected within 32
switching cycles, the LM27402 then enters into a hiccup mode
state. During hiccup mode, the LM27402 will shutdown for
1.28 ms and then attempt to restart again. When transitioning
into hiccup mode, the high-side FET is turned off and the low-
side FET is turned on. As the inductor current reaches zero
subsequent to the over-current event, the low-side FET is
turned off and the switch-node becomes high impedance to
prepare for the next startup sequence. The soft-start capaci-
tor is discharged through an internal pull-down FET to reini-
tialize the startup sequence. To illustrate how the LM27402
behaves during current limit faults, an over-current scenario
is illustrated in Figure 2.
11
www.national.com
LM27402
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相關代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM27402SQX/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM27403 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Synchronous Buck Controller with Temperature-Compensated, Inductor-DCR-Based Overcurrent Protection and Programmable Thermal Shutdown |
| LM27403EVM | 制造商:Texas Instruments 功能描述:LM27403EVM - Boxed Product (Development Kits) |
| LM27403EVM-POL600 | 制造商:Texas Instruments 功能描述:BOARD EVAL LM27403 |
| LM27403SQ | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Synchronous Buck Controller with Temperature-Compensated, Inductor-DCR-Based Overcurrent Protection and Programmable Thermal Shutdown |
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