参数资料
型号: LTC3867EUF#PBF
厂商: Linear Technology
文件页数: 25/36页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 24-QFN
产品培训模块: LTC3867 Synchronous Step-Down DC/DC Controller
标准包装: 91
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1.2MHz
占空比: 98%
电源电压: 4 V ~ 38 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: 24-WFQFN 裸露焊盘
包装: 管件
LTC3867
APPLICATIONS INFORMATION
the soft-start phase expires, the LTC3867 is forced into
continuous mode of operation as soon as V FB is below
the undervoltage threshold of 0.555V regardless of the
setting on the MODE pin. However, the LTC3867 should
always be set in forced continuous mode tracking down
when there is no load. After TK/SS drops below 0.1V, the
controller operates in discontinuous mode.
The LTC3867 allows the user to program how its output
ramps up and down by means of the TK/SS pin. Through
these pins, the output can be set up to either coincidentally
or ratiometrically track another supply’s output, as shown
in Figure 10. In the following discussions, V OUT2 refers to
the LTC3867’s output as a slave and V OUT1 refers to another
supply output as a master. To implement the coincident
tracking in Figure 10a, connect an additional resistive di-
vider to V OUT1 and connect its mid-point to the TK/SS pin
of the slave controller. The ratio of this divider should be
V OUT1
V OUT2
the same as that of the slave controller’s feedback divider
shown in Figure 11a. In this tracking mode, V OUT1 must
be set higher than V OUT2 . To implement the ratiometric
tracking in Figure 10b, the ratio of the V OUT2 divider should
be exactly the same as the master controller’s feedback
divider shown in Figure 11b . By selecting different resis-
tors, the LTC3867 can achieve different modes of tracking
including the two in Figure 10.
So which mode should be programmed? While either
mode in Figure 10 satisfies most practical applications,
some trade-offs exist. The ratiometric mode saves a pair
of resistors, but the coincident mode offers better output
regulation. Under ratiometric tracking, when the master
controller’s output experiences dynamic excursion (under
load transient, for example), the slave controller output
will be affected as well. For better output regulation, use
the coincident tracking mode instead of ratiometric.
V OUT1
V OUT2
TIME
TIME
3867 F10
(10a) Coincident Tracking
(10b) Ratiometric Tracking
Figure 10. Two Different Modes of Output Voltage Tracking
V OUT1
V OUT2
V OUT1
V OUT2
TO
TK/SS2
PIN
R3
R4
R1
R2
TO
V FB1
PIN
TO
V FB2
PIN
R3
R4
TO
TK/SS2
PIN
R1
R2
TO
V FB1
PIN
TO
V FB2
PIN
R3
R4
3867 F11
(11a) Coincident Tracking Setup
(11b) Ratiometric Tracking Setup
Figure 11. Setup and Coincident and Ratiometric Tracking
3867f
25
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LTC3868EGN-1#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR)
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