参数资料
型号: LT3686HDD#TRPBF
厂商: Linear Technology
文件页数: 22/28页
文件大小: 0K
描述: IC REG BUCK ADJ 1.2A 10DFN
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.8 V ~ 30 V
输入电压: 3.6 V ~ 37 V
PWM 型: 电流模式
频率 - 开关: 300kHz ~ 2.5MHz
电流 - 输出: 1.2A
同步整流器:
工作温度: -40°C ~ 150°C
安装类型: 表面贴装
封装/外壳: 10-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 10-DFN(3x3)
LT3686
APPLICATIONS INFORMATION
Frequency Compensation
The LT3686 uses current mode control to regulate the
output. This simplifies loop compensation. In particular,
the LT3686 does not require the ESR of the output capaci-
tor for stability allowing the use of ceramic capacitors to
achieve low output ripple and small circuit size. Figure 16
shows an equivalent circuit for the LT3686 control loop.
The error amp is a transconductance amplifier with finite
output impedance. The power section, consisting of the
modulator, power switch and inductor, is modeled as a
transconductance amplifier generating an output current
proportional to the voltage at the V C node. Note that the
output capacitor integrates this current, and that the capaci-
tor on the V C node (C C ) integrates the error amplifier output
current, resulting in two poles in the loop. R C provides a
zero. With the recommended output capacitor, the loop
crossover occurs above the R C C C zero. This simple model
works well as long as the value of the inductor is not too
high and the loop crossover frequency is much lower than
the switching frequency. With a larger ceramic capacitor
(very low ESR), crossover may be lower and a phase lead
capacitor (CPL) across the feedback divider may improve
the phase margin and transient response. Large electrolytic
capacitors may have an ESR large enough to create an
additional zero, and the phase lead may not be necessary.
If the output capacitor is different than the recommended
capacitor, stability should be checked across all operating
conditions, including load current, input voltage and tem-
perature. The LT1375 data sheet contains a more thorough
discussion of loop compensation and describes how to
test the stability using a transient load.
LT3686
1V
CURRENT MODE
POWER STAGE
g m =
2A/V
SW
OUT
FB
R1
C PL
GND
V C
R C
160k
C C
100pF
g m =
200μA/V
ERROR
AMPLIFIER
1M
800mV
R2
+
ESR
C1
C1
3686 F16
Figure 16. Model for Loop Response
3686fc
22
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