参数资料
型号: LTC3785EUF#PBF
厂商: Linear Technology
文件页数: 14/20页
文件大小: 0K
描述: IC REG CTRLR BST PWM VM 24-QFN
标准包装: 91
PWM 型: 电压模式
输出数: 2
频率 - 最大: 1MHz
占空比: 99%
电源电压: 2.7 V ~ 10 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 24-WFQFN 裸露焊盘
包装: 管件
产品目录页面: 1336 (CN2011-ZH PDF)
LTC3785
APPLICATIONS INFORMATION
1.6 ? V OUT 2
G BOOST = , Boost Mode
f FILTER _ POLE =
f UG =
CLOSINGTHEFEEDBACKLOOP
The LTC3785 incorporates voltage mode control. The
control to output gain is given by:
G BUCK = 1.6 ? V IN , Buck Mode
V IN
The output filter exhibits a double-pole response and is
given by:
1
2 ? π ? L ? C OUT
where C OUT is the output filter capacitor.
A simple Type I compensation network (Figure 5) can be
incorporated to stabilize the loop but at a cost of reduced
bandwidth and slower transient response. To ensure proper
phase margin, the loop must cross over almost a decade
before the L-C double pole.
The unity gain frequency of the error amplifier with the
Type I compensation is given by:
1
2 ? π ?R1? C P1
Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a higher
bandwidth, Type III compensation is required as shown
in Figure 6. Two zeros are required to compensate for the
double pole response.
f FILTER _ ZERO =
V IN 2
2 ? π ?I OUT ?L ? V OUT
Theoutputfilterzeroisgivenby:
1
2 ? π ?R ESR ? C OUT
where R ESR is the capacitor equivalent series resistance.
A troublesome feature in boost mode is the right half plane
zero (RHP), and is given by:
f RHPZ =
f POLE1 ≈
f ZERO1 =
f ZERO2 =
f POLE2 ≈
1
2 ? π ? 32e3 ? C P1 ?R1
1
2 ? π ?R Z ? C P1
1
2 ? π ?R1? C Z1
1
2 ? π ?R Z ? C P2
(a very low frequency)
The loop gain is typically rolled off before the RHP zero
frequency.
+
ERROR
AMP
1.225V
FB
V OUT
R1
+
ERROR
AMP
1.225V
FB
V OUT
R1
C Z1
V C
C P1
R2
V C
R Z
C P1
R2
3785 F05
C P2
3785 F06
Figure 5. Error Amplifier with Type I Compensation
Figure 6. Error Amplifier with Type III Compensation
3785fc
  
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