参数资料
型号: LTC3814IFE-5#TRPBF
厂商: Linear Technology
文件页数: 14/30页
文件大小: 0K
描述: IC REG CTRLR BST PWM CM 16-TSSOP
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
占空比: 90%
电源电压: 4.5 V ~ 55 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: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
LTC3814-5
APPLICATIONS INFORMATION
voltage changes, tie the V OFF pin to a resistive divider from
V IN , as shown in Figure 5. Choose the resistor values so
that the V RNG voltage equals about 1.55V at the mid-point
of V IN as follows:
Changes in the load current magnitude will also cause
a frequency shift. Parasitic resistance in the MOSFET
switches and inductor reduce the effective voltage across
the inductance, resulting in increased duty cycle as the
V IN,MID =
V IN(MAX) + V IN(MIN)
2
= 1.55V ? 1 +
R1
R2
load current increases. By shortening the off-time slightly
as current increases, constant-frequency operation can be
maintained. This is accomplished with a resistor connected
f =
1 + R1/ R2
With  these  resistor  values,  the  frequency  will  remain
relatively constant at:
(Hz)
R OFF (76pF)
for the range of 0.45V IN to 1.55 ? V IN , and will be propor-
tional to V IN outside of this range.
1000
from the I TH pin to the I OFF pin to increase the I OFF current
slightly as V ITH increases. The values required will depend
on the parasitic resistances in the speci?c application. A
good starting point is to feed about 10% of the R OFF cur-
rent with R ITH as shown in Figure 6.
1000
1+R1/R2 = 3.2
(V IN , MID = 5V)
V IN = 5V
V IN = 24V
1+R1/R2 = 7.7
(V IN , MID =12V)
V IN = 12V
1+R1/R2 = 15.5
(V IN , MID = 24V)
100
10
100
1000
100
10
100
1000
R OFF (kΩ)
38145 F04a
R OFF (kΩ)
38145 F04b
Figure 4a. Switching Frequency vs R OFF (V OFF = INTV CC )
V IN
R1
Figure 4b. Switching Frequency vs R OFF
(V OFF Connected to a Resistor Divider from V IN )
V OFF
V OUT
R OFF
I OFF
R2
LTC3814-5
1000pF
R ITH
LTC3814-5
I TH
38145 F05
R ITH =
10R OFF
V OUT
38145 F06
Figure 5. V OFF Connection to Keep the Operating
Frequency Constant as the Input Supply Varies
Figure 6. Correcting Frequency Shift with Load Current Changes
38145fc
14
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