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參數(shù)資料
| 型號： | LTC3112IFE#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 12 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-20 |
| 文件頁數(shù)： | 16/32頁 |
| 文件大?。?/td> | 651K |
| 代理商： | LTC3112IFE#PBF |
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LTC3112
23
3112f
both higher order poles (fPOLE2 and fPOLE3) occur at the
common frequency, fP. In most cases this is a reasonable
assumption since the zeros are typically located between
1kHz and 10kHz and the poles are typically located near
each other at much higher frequencies. Given this as-
sumption, the maximum phase boost,
φMAX, provided by
the compensated error amplier is determined simply by
the amount of separation between the poles and zeros as
shown by the following equation.
φMAX = 4tan
–1
fP
f Z
– 270°
A reasonable choice is to pick the frequency of the poles,
fP, to be about 50 times higher than the frequency of the
zeros, fZ, which provides a peak phase boost of approxi-
mately
φMAX = 60° as was assumed previously. Next, the
phase boost must be centered so that the peak phase
occurs at the target crossover frequency. The frequency
of the maximum phase boost, fCENTER, is the geometric
mean of the pole and zero frequencies as shown below.
f
CENTER =
f
P fZ =
50 f
Z 7fZ
Therefore, in order to center the phase boost given a fac-
tor of 50 separation between the pole and zero frequen-
cies, the zeros should be located at one seventh of the
crossover frequency and the poles should be located at
seven times the crossover frequency as given by the fol-
lowing equations.
f
Z =
1
7
f
C =
1
7
35kHz
()=5kHz
f
P = 7fC = 735kHz
()=250kHz
This placement of the poles and zeros will yield a peak phase
boost of 60° that is centered at the crossover frequency,
fC. Next, in order to produce the desired target crossover
frequency, the gain of the compensation network at the
point of maximum phase boost, GCENTER, must be set to
7dB. The gain of the compensated error amplier at the
point of maximum phase gain is given by the following
equation.
G
CENTER = 10log
2
πf
P
2
πf
Z
()3 R
TOP CFB
()2
dB
Assuming a multiple of 50 separation between the pole
frequencies and zero frequencies this can be simplied
to the following expression.
G
CENTER = 20log
50
2
πf
CRTOP CFB
dB
This equation completes the set of constraints needed to
determine the compensation component values. Speci-
cally, the two zeros, fZERO1 and fZERO2, should be located
near 5kHz. The two poles, fPOLE2 and fPOLE3, should be
located near 250kHz and the gain should be set to provide
a gain at the crossover frequency of GCENTER = –7dB.
The rst step in dening the compensation component
values is to pick a value for RTOPthatprovidesanacceptably
low quiescent current through the resistor divider. A value
of RTOP = 845kΩ is a reasonable choice and is used in
several applications circuits. Next, the value of CFB can
be found in order to set the error amplier gain at the
crossover frequency to 7dB as follows.
GCENTER = –7 dB = 20log
50
2
π 35kHz
() 845kΩ
()C
FB
CFB =
50
0.185
10
12 alog
–7
20
680 pF
The compensation poles can be set at 250kHz and the
zeros at 5kHz by using the expressions for the pole and
zero frequencies given in the previous section. Setting the
frequency of the rst zero fZERO1, to 5kHz results in the
following value for RFB.
R
FB =
1
2
π 680pF
() 5kHz
()
45kΩ
A 33kΩ was selected to split the two zeros slightly apart,
giving a higher zero frequency of 7kHz. This leaves the
APPLICATIONS INFORMATION
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PDF描述 |
|---|---|
| LTC3112EFE#PBF | 12 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO20 |
| LTC3112EDHD#PBF | 12 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO16 |
| LTC3112EDHD#TRPBF | 12 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PDSO16 |
| LTC3113EFE#PBF | 16 A SWITCHING REGULATOR, 2000 kHz SWITCHING FREQ-MAX, PDSO20 |
| LTC3113IDHD#TRPBF | 16 A SWITCHING REGULATOR, 2000 kHz SWITCHING FREQ-MAX, PDSO16 |
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