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| 型号： | MIC2179-3.3BSM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 8/13页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 3.3V 20SSOP |
| 标准包装： | 1,000 |
| 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： | 1.5A |
| 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-SSOP（0.209"，5.30mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 20-SSOP |
| 其它名称： | MIC2179-3.3BSMTR MIC2179-3.3BSMTR-ND |
Micrel, Inc.
(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 the 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 dis-
sipation 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.
Skip-Mode Operation
Refer to “Skip Mode Functional Diagram” which is a simplified
block diagram of the MIC2179 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-chan-
nel is kept off to optimize efficiency by reducing gate charge
dissipation. V OUT is regulated by skipping switching cycles
that turn on the P-channel.
To begin analyzing MIC2179 skip mode operation, assume
the skip-mode comparator output is high and the latch out-
put 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 400mA. When I L1 reaches this value, the current limit
comparator sets the RS latch output to logic 0, turning off
MIC2179
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 decreases 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, and this begins
another switching cycle.
The skip-mode comparator regulates V OUT by controlling
when the MIC2179 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 com-
parator 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 MIC2179 to always supply up to 300mA of
load current when operating in skip mode.
Selecting PWM- or Skip-Mode Operation
PWM or skip mode operation is selected by an external
logic signal applied to the PWM pin. A logic low places the
MIC2179 into PWM mode, and logic high places it into skip
mode. Skip mode operation provides the best efficiency when
load current is less than 150mA, and PWM operation is more
efficient at higher currents.
The MIC2179 was designed to be used in intelligent sys-
tems that determine when it should operate in PWM or skip
mode. This makes the MIC2179 ideal for applications where
a regulator must guarantee low noise operation when sup-
plying light load currents, such as cellular telephone, audio,
and multimedia circuits.
There are two important items to be aware of when selecting
PWM or skip mode. First, the MIC2179 can start-up only in
PWM mode, and therefore requires a logic low at PWM dur-
ing start-up. Second, in skip mode, the MIC2179 will supply
a maximum load current of approximately 300mA, so the
output will drop out of regulation when load current exceeds
this limit. To prevent this from occurring, the MIC2179 should
change from skip to PWM mode when load current exceeds
200mA.
June 2009
8
M9999-063009
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MIC2179-5.0BSM | 功能描述:直流/直流开关调节器 1.5A 200kHz Synchronous Switcher in SSOP Pkg 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 |
| MIC2179-5.0BSM TR | 功能描述:直流/直流开关调节器 1.5A 200kHz Synchronous Switcher in SSOP Pkg 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 |
| MIC2179-5.0YSM | 功能描述:直流/直流开关调节器 1.5A 200kHz Synchronous Switcher in SSOP Pkg (Lead Free) 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 |
| MIC2179-5.0YSM TR | 功能描述:直流/直流开关调节器 1.5A 200kHz Synchronous Switcher in SSOP Pkg (Lead Free) 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 |
| MIC2179-5.0YSMTR | 制造商:RF Micro Devices Inc 功能描述: |
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