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参数资料
| 型号： | MIC2177-3.3YWM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 9/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 3.3V 20SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 4.5 V ~ 16.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz |
| 电流 - 输出： | 2.5A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-SOIC（0.295"，7.50mm 宽） |
| 包装： | 标准包装 |
| 供应商设备封装： | 20-SOIC（宽型） |
| 产品目录页面： | 1092 (CN2011-ZH PDF) |
| 其它名称： | 576-1542-6 |
Micrel, Inc.
discharged from the inductor and I L1 decreases until the
next switching cycle begins. By varying the P-channel
on-time (duty cycle), the average inductor current is
adjusted to whatever value is required to regulate the
output voltage.
The MIC2177 uses current-mode control to adjust the
duty cycle and regulate the output voltage. Current-
mode control has two signal loops that determine the
duty cycle. One is an outer loop that senses the output
voltage, and the other is a faster inner loop that senses
the inductor current. Signals from these two loops
control the duty cycle in the following way: V OUT is fed
back to the error amplifier which compares the feedback
voltage (V FB ) to an internal reference voltage (V REF ).
When V OUT is lower than its nominal value, the error
amplifier output voltage increases. This voltage then
intersects the current-sense waveform later in switching
period which increases the duty cycle and average
inductor current. If V OUT is higher than nominal, the error
amplifier output voltage decreases, reducing the duty
cycle.
The PWM control loop is stabilized in two ways. First,
the inner signal loop is compensated by adding a
corrective ramp to the output of the current sense
amplifier. This allows the regulator to remain stable
when operating at greater than 50% duty cycle. Second,
a series resistor-capacitor load is connected to the error
amplifier output (COMP pin). This places a pole-zero
pair in the regulator control loop.
One more important item is synchronous rectification. As
mentioned earlier, the N-channel output MOSFET is
turned on after the P-channel turns off. When the N-
channel turns on, its on-resistance is low enough to
create a short across the output diode. As a result,
inductor current flows through the N-channel and the
voltage drop across; it is significantly lower than a diode
forward voltage. This reduces power dissipation and
improves efficiency to greater than 95% under certain
operating conditions.
To prevent shoot through current, the output stage
employs break-before-make circuitry that provides
approximately 50ns of delay from the time one MOSFET
turns off and the other turns on. As a result, inductor
current briefly flows through the output diode during this
transition.
MIC2177
switching cycles that turn on the P-channel.
To begin analyzing MIC2177 skip-mode operation,
assume the skip-mode comparator output is high and
the latch output has been reset to a logic 1. This turns on
the P-channel and causes I L1 to increase linearly until it
reaches a current limit of 600mA. When I L1 reaches this
value, the current limit comparator sets the RS latch
output to logic 0, turning off the P-channel. The output
switch voltage (V SW ) then swings from V IN to 0.4V below
ground, and I L1 flows through the Schottky diode. L1
discharges its energy to the output and I L1 de-creases to
zero. When I L1 = 0, V SW swings from –0.4V to V OUT , and
this triggers a one-shot that resets the RS latch.
Resetting the RS latch turns on the P-channel, which
begins another switching cycle.
The skip-mode comparator regulates V OUT by controlling
when the MIC2177 skips cycles. It compares V FB to V REF
and has 10mV of hysteresis to prevent oscillations in the
control loop. When V FB is less than V REF – 5mV, the
comparator output is logic 1, allowing the P-channel to
turn on. Conversely, when V FB is greater than V REF +
5mV, the P-channel is turned off.
Note that this is a self-oscillating topology which explains
why the switching frequency and duty cycle are a
function of V IN , V OUT , and the value of L1. It has the
unique feature (for a pulse-skipping regulator) of
supplying the same value of maximum load current for
any value of V IN , V OUT , or L1. This allows the MIC2177 to
always supply up to 300mA of load current (I LOAD ) when
operating in skip mode.
Changing from PWM to Skip Mode
Refer to “Block Diagram” for circuits described in the
following sections.
The MIC2177 automatically changes from PWM to skip
mode operation when I LOAD drops below a minimum
value. I MIN is determined indirectly by detecting when the
peak inductor current (I L(peak) ) is less than 420mA. This is
done by the minimum current comparator which detects
if the output P-Channel current equals 420mA during
each switching cycle. If it does not, the PWM/skip-mode
select logic places the MIC2177 into skip-mode
operation.
The value of I MIN that corresponds to I L1(peak) = 420mA is
given by the following equation:
Skip-Mode Operation
Refer to “Skip-Mode Functional Diagram” which is a
I MIN =
420mA ? ? I L1
2
simplified block diagram of the MIC2177 operating in
skip mode and its associated waveforms.
Skip-mode operation turns on the output P-channel at a
frequency and duty cycle that is a function of V IN , V OUT ,
and the output inductor value. While in skip mode, the N-
channel is kept off to optimize efficiency by reducing
gate charge dissipation. V OUT is regulated by skipping
Where:
? I L1 = inductor ripple current
This equation shows I MIN varies as a function of ? I L .
Therefore, the user must select an inductor value that
results in I MIN = 200mA when I L(peak) = 420mA. The
formulas for calculating the correct inductor value are
April 2008
9
M9999-042108
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MIC2177-5.0BWM | 功能描述:直流/直流开关调节器 2.5A 200kHz Synchronous Switcher RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MIC2177-5.0BWM TR | 功能描述:直流/直流开关调节器 2.5A 200kHz Synchronous Switcher RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MIC2177-5.0BWMTR | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| MIC2177-5.0YWM | 功能描述:直流/直流开关调节器 2.5A 200kHz Synchronous Switcher RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MIC2177-5.0YWM TR | 功能描述:直流/直流开关调节器 2.5A 200kHz Synchronous Switcher RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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