参数资料
型号: LT1107CN8
厂商: Linear Technology
文件页数: 10/16页
文件大小: 0K
描述: IC REG BUCK BST INV ADJ .4A 8DIP
标准包装: 50
类型: 降压(降压),升压(升压),反相
输出类型: 可调式
输出数: 1
输出电压: 可调
输入电压: 2 V ~ 30 V
频率 - 开关: 63kHz
电流 - 输出: 400mA
同步整流器:
工作温度: 0°C ~ 70°C
安装类型: 通孔
封装/外壳: 8-DIP(0.300",7.62mm)
包装: 管件
供应商设备封装: 8-PDIP
LT1107
A PPLICATI
S I FOR ATIO
? V OUT ? should be less than 6.2V. More negative output
voltages can be accommodated as in the prior section.
In Figure 4, the input is negative while the output is
positive. In this configuration, the magnitude of the input
voltage can be higher or lower than the output voltage. A
level shift, provided by the PNP transistor, supplies proper
polarity feedback information to the regulator.
Using the I LIM Pin
The LT1107 switch can be programmed to turn off at a set
switch current, a feature not found on competing devices.
This enables the input to vary over a wide range without
exceeding the maximum switch rating or saturating the
inductor. Consider the case where analysis shows the
LT1107 must operate at an 800mA peak switch current
with a 2V input. If V IN rises to 4V, the peak switch current
+V IN
+
will rise to 1.6A, exceeding the maximum switch current
C2
R3
rating. With the proper resistor selected (see the “Maxi-
I LIM
V IN
LT1107
SW1
FB
L1
mum Switch Current vs R LIM ” characteristic), the switch
current will be limited to 800mA, even if the input voltage
increases.
GND
SW2
D1
1N5818
+
C1
R1
R2
Another situation where the I LIM feature is useful occurs
when the device goes into continuous mode operation.
This occurs in step-up mode when:
Figure 3. Positive-to-Negative Converter
–V OUT
1107 F03
V OUT + V DIODE
V IN ? V SW
<
1
1 ? DC
( 24 )
C1
( )
V OUT = 1.25V + 0.6V
–V IN
+
C2
R3
LT1107
GND SW2
I LIM V IN
SW1
FB
L1
R2
D1
+
R1
R2
+V OUT
R1
2N3906
1107 F04
When the input and output voltages satisfy this relation-
ship, inductor current does not go to zero during the
switch OFF time. When the switch turns on again, the
current ramp starts from the non-zero current level in the
inductor just prior to switch turn-on. As shown in Figure
5, the inductor current increases to a high level before the
comparator turns off the oscillator. This high current can
cause excessive output ripple and requires oversizing the
output capacitor and inductor. With the I LIM feature, the
switch turns off at the programmed current as shown in
Figure 4. Negative-to-Positive Converter
Figure 6, keeping output ripple to a minimum.
1107fa
10
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