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参数资料
| 型号： | LT1107IS8#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST INV ADJ 8SOIC |
| 标准包装： | 2,500 |
| 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： | 无 |
| 工作温度： | -45°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
LT1107
A PPLICATI
S I FOR ATIO
The usual step-up configuration for the LT1107 is shown
in Figure 1. The LT1107 first pulls SW1 low causing V IN –
V CESAT to appear across L1. A current then builds up in L1.
At the end of the switch ON time the current in L1 is 1 :
V IN
+
C2
R3
100 ?
V IN
I LIM
SW1
FB
I PEAK = IN t ON
V
L
L1
D1
( 20 )
LT1107
GND
SW2
L1
D1
1N5818
+
C1
R2
V OUT
V IN
R3
V OUT
R1
I LIM
V IN
R2
1107 F02
LT1107
SW1
+
C1
Figure 2. Step-Down Mode Hookup
FB
When the switch turns off, the SW2 pin falls rapidly and
GND
SW2
R1
actually goes below ground. D1 turns on when SW2
reaches 0.4V below ground. D1 MUST BE A SCHOTTKY
1107 F01
Figure 1. Step-Up Mode Hookup
Immediately after switch turn-off, the SW1 voltage pin
starts to rise because current cannot instantaneously stop
DIODE. The voltage at SW2 must never be allowed to go
below –0.5V. A silicon diode such as the 1N4933 will allow
SW2 to go to –0.8V, causing potentially destructive power
dissipation inside the LT1107. Output voltage is deter-
mined by:
V OUT = ? 1 +
flowing in L1. When the voltage reaches V OUT + V D , the
inductor current flows through D1 into C1, increasing
V OUT . This action is repeated as needed by the LT1107 to
?
?
R 2 ?
R 1 ? ?
(
1 . 25 V
)
( 23 )
keep V FB at the internal reference voltage of 1.25V. R1 and
R2 set the output voltage according to the formula:
R3 programs switch current limit. This is especially im-
portant in applications where the input varies over a wide
(
)
V OUT = ? 1 + ? 1 . 25 V
? R 2 ?
? R 1 ?
Step-Down (Buck Mode) Operation
( 21 )
range. Without R3, the switch stays on for a fixed time
each cycle. Under certain conditions the current in L1 can
build up to excessive levels, exceeding the switch rating
and/or saturating the inductor. The 100 ? resistor pro-
grams the switch to turn off when the current reaches
A step-down DC/DC converter converts a higher voltage to
a lower voltage. The usual hookup for an LT1107 based
step-down converter is shown in Figure 2.
When the switch turns on, SW2 pulls up to V IN – V SW . This
puts a voltage across L1 equal to V IN – V SW – V OUT ,
causing a current to build up in L1. At the end of the switch
ON time, the current in L1 is equal to:
approximately 700mA. When using the LT1107 in step-
down mode, output voltage should be limited to 6.2V or
less. Higher output voltages can be accommodated by
inserting a 1N5818 diode in series with the SW2 pin
(anode connected to SW2).
Inverting Configurations
The LT1107 can be configured as a positive-to-negative
I PEAK =
V IN ? V SW ? V OUT
L
t ON
( 22 )
converter (Figure 3), or a negative-to-positive converter
(Figure 4). In Figure 3, the arrangement is very similar to
a step-down, except that the high side of the feedback is
Note 1: This simple expression neglects the effects of switch and coil
resistance. This is taken into account in the “Inductor Selection” section.
referred to ground. This level shifts the output negative. As
in the step-down mode, D1 must be a Schottky diode, and
1107fa
9
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