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| 型号： | MIC2168YMM |
| 厂商： | Micrel Inc |
| 文件页数： | 10/14页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 10-MSOP |
| 标准包装： | 100 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1.1MHz |
| 占空比： | 90% |
| 电源电压： | 3 V ~ 14.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1092 (CN2011-ZH PDF) |
| 其它名称： | 576-1708-5 MIC2168YMM-ND |
Error
V O = V REF × ? 1 + ?
V REF × R1
G (S) - ? ?
? DCR × S × C + S × L × C + 1 + ESR × S × C ?
MIC2168
I C IN (RMS) ≈ I OUT ( MAX ) × D × (1 ? D)
The power dissipated in the input capacitor is:
P DISS(C IN ) = I C IN (RMS) 2 × R ESR(C IN )
Voltage Setting Components
The MIC2168 requires two resistors to set the output voltage
as shown in Figure 2.
R1
Amp FB
7
R2
V REF
0.8V
MIC2168 [adj.]
Figure 2. Voltage-Divider Con?guration
Where:
V REF for the MIC2168 is typically 0.8V
The output voltage is determined by the equation:
? R1 ?
? R2 ?
A typical value of R1 can be between 3k ? and 10k ? . If R1 is
too large, it may allow noise to be introduced into the voltage
feedback loop. If R1 is too small, in value, it will decrease the
ef?ciency of the power supply, especially at light loads. Once
R1 is selected, R2 can be calculated using:
R2 =
V O ? V REF
External Schottky Diode
An external freewheeling diode is used to keep the inductor
current ?ow continuous while both MOSFETs are turned off.
This dead time prevents current from ?owing unimpeded
through both MOSFETs and is typically 15ns. The diode
conducts twice during each switching cycle. Although the
average current through this diode is small, the diode must
be able to handle the peak current.
The reverse voltage requirement of the diode is:
V DIODE(RRM) = V IN
The power dissipated by the Schottky diode is:
P DIODE = I D(AVG) × V F
where:
Micrel, Inc.
V F = forward voltage at the peak diode current
The external Schottky diode, D1, is not necessary for circuit
operation since the low-side MOSFET contains a parasitic
body diode. The external diode will improve ef?ciency and
decrease high frequency noise. If the MOSFET body diode
is used, it must be rated to handle the peak and average cur-
rent. The body diode has a relatively slow reverse recovery
time and a relatively high forward voltage drop. The power
lost in the diode is proportional to the forward voltage drop
of the diode. As the high-side MOSFET starts to turn on, the
body diode becomes a short circuit for the reverse recovery
period, dissipating additional power. The diode recovery and
the circuit inductance will cause ringing during the high-side
MOSFET turn-on. An external Schottky diode conducts at
a lower forward voltage preventing the body diode in the
MOSFET from turning on. The lower forward voltage drop
dissipates less power than the body diode. The lack of a
reverse recovery mechanism in a Schottky diode causes
less ringing and less power loss. Depending on the circuit
components and operating conditions, an external Schottky
diode will give a 1 / 2 % to 1% improvement in ef?ciency.
Feedback Loop Compensation
The MIC2168 controller comes with an internal transcon-
ductance error ampli?er used for compensating the voltage
feedback loop by placing a capacitor (C1) in series with a
resistor (R1) and another capacitor C2 in parallel from the
COMP pin to ground. See “Functional Block Diagram.”
Power Stage
The power stage of a voltage mode controller has an induc-
tor, L1, with its winding resistance (DCR) connected to the
output capacitor, C OUT , with its electrical series resistance
(ESR) as shown in Figure 3. The transfer function G(s), for
such a system is:
L DCR
V O
ESR
C OUT
Figure 3. The Output LC Filter in a Voltage Mode
Buck Converter
? (1 + ESR × S × C) ?
2
Plotting this transfer function with the following assumed values
(L=2 μ H, DCR=0.009 ? , C OUT =1000 μ F, ESR=0.050 ? ) gives
lot of insight as to why one needs to compensate the loop by
adding resistor and capacitors on the COMP pin. Figures 4
and 5 show the gain curve and phase curve for the above
transfer function.
M9999-040805
10
April 2005
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| MIC2168YMM TR | 功能描述:直流/直流开关调节器 Replaced by MIC2168AYMM TR (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 |
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