参数资料
型号: MIC2155YML TR
厂商: Micrel Inc
文件页数: 32/35页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 32MLF
特色产品: MIC2155/6 Buck Control IC
标准包装: 1
PWM 型: 电压模式
输出数: 1
频率 - 最大: 550kHz
占空比: 80%
电源电压: 4.5 V ~ 14.5 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 32-VFQFN 裸露焊盘,32-MLF?
包装: 标准包装
产品目录页面: 1091 (CN2011-ZH PDF)
其它名称: 576-3527-6
Micrel, Inc.
Unlike the voltage output amplifier used for Channel 1
compensation, a transconductance amplifier is used for
the Channel 2 compensation since only a pole/zero
combination is required for compensation. The
transconductance amplifier transfer function is:
MIC2155/2156
The loop is inherently stable because the phase shift is
only 90 degrees. The error amplifier pole and zero is
selected to achieve a desired crossover frequency. In
this example, the desired crossover frequency is 50kHz.
The transfer function of the filter, modulator and
feedback is plotted in Figure 28.
Gea ( s ) = gm ×
1 + s × Rz1 × Cz1
s × Cz 1
Where:
Rz1 and Cz1 are the external components connected to
the COMP2 pin
gm is the transconductance of the internal amplifier.
The pole and zero frequencies are:
50
0
-50
Phase
V IN = 12V
V OUT = 1.8V
L = 1.5μH
Gain
f POLE =
f ZERO =
gm
2 × π × Cz 1
1
2 × π × Rz 1 × Cz 1
-100
10 100 1k 10k 100k 1M
FREQUENCY
Figure 28. Current Sharing Loop Gain/Phase
The gain boost required at 50kHz is 28dB which is a
gain of 25. The gain for frequencies above the zero is:
The gain of the modulator is:
G MID = Rz 1 × gm
g MOD =
1
V M
For a typical gm = 1.25mS, solving for Rz1:
Where:
V M is the peak-to-peak amplitude of the internal
sawtooth.
Rz 1 =
G MID
gm
=
25
1 . 25 mS
= 20 k Ω
G FILTER ( s ) = IN
Cz 1 =
Cz 1 =
= 800 pF
G OL 2 ( s ) = G EA ( s ) MOD × H × G FILTER ( s ) =
The gain of the feedback circuit is output current divide
by V EA
H = R L 2
The filter transfer function is the output current over the
applied voltage:
V ? V OUT
s × L 2
The open loop transfer function is:
× G
gm × ( 1 + s × Rz1 × Cz1 ) × R L 2 × ( V IN ? V OUT )
( s × Cz 1 ) × Vm × ( s × L 2 )
Set the zero frequency to be 1/5 of the crossover
frequency:
1
2 × π × Rz 1 × fz 1
1
2 × π × 20 k × 10 k
The compensated open loop gain/phase plot is shown in
Figure 29.
November 2009
32
M9999-111209-B
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