参数资料
型号: LT1110CS8-12#TRPBF
厂商: Linear Technology
文件页数: 10/16页
文件大小: 0K
描述: IC REG BUCK BOOST 12V 0.4A 8SOIC
标准包装: 2,500
类型: 降压(降压),升压(升压)
输出类型: 固定
输出数: 1
输出电压: 12V
输入电压: 1 V ~ 30 V
频率 - 开关: 70kHz
电流 - 输出: 400mA
同步整流器:
工作温度: 0°C ~ 70°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
LT1110
A PPLICATI
Diode Selection
S I FOR ATIO
Immediately after switch turn off, the SW1 voltage pin
Speed, forward drop, and leakage current are the three
main considerations in selecting a catch diode for LT1110
converters. General purpose rectifiers such as the 1N4001
are unsuitable for use in any switching regulator applica-
tion. Although they are rated at 1A, the switching time of
a 1N4001 is in the 10 μ s-50 μ s range. At best, efficiency will
starts to rise because current cannot instantaneously stop
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 LT1110 to
keep V FB at the internal reference voltage of 220mV. R1
and R2 set the output voltage according to the formula
V OUT = ? 1 +
(
)
R 1 ?
be severely compromised when these diodes are used; at
worst, the circuit may not work at all. Most LT1110 circuits
will be well served by a 1N5818 Schottky diode, or its
?
?
R 2 ?
? 220 mV .
( 21 )
surface mount equivalent, the MBRS130T3. The combina-
tion of 500mV forward drop at 1A current, fast turn ON and
turn OFF time, and 4 μ A to 10 μ A leakage current fit nicely
with LT1110 requirements. At peak switch currents of
100mA or less, a 1N4148 signal diode may be used. This
diode has leakage current in the 1nA-5nA range at 25 ° C
and lower cost than a 1N5818. (You can also use them to
get your circuit up and running, but beware of destroying
Step-Down (Buck Mode) Operation
A step-down DC-DC converter converts a higher voltage
to a lower voltage. The usual hookup for an LT1110 based
step-down converter is shown in Figure 5.
V IN
R3
220 ?
the diode at 1A switch currents.)
+
C2
I LIM
V IN
SW1
FB
Step-Up (Boost Mode) Operation
LT1110
L1
A step-up DC-DC converter delivers an output voltage
higher than the input voltage. Step-up converters are not
GND
SW2
D1
+
R2
V OUT
short circuit protected since there is a DC path from input
1N5818
C1
R1
to output.
I PEAK =
t ON ( 20 )
The usual step-up configuration for the LT1110 is shown
in Figure 4. The LT1110 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
L
LT1110 ? TA15
Figure 5. Step-Down Mode Hookup
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
V IN
R3*
L1
D1
V OUT
I PEAK =
V IN ? V SW ? V OUT
L
t ON .
( 22 )
I LIM
V IN
SW1
R2
+
When the switch turns off, the SW2 pin falls rapidly and
actually goes below ground. D1 turns on when SW2
LT1110
FB
C1
reaches 0.4V below ground. D1 MUST BE A SCHOTTKY
GND
SW2
R1
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
* = OPTIONAL
10
Figure 4. Step-Up Mode Hookup.
LT1110 ? TA14
Note 1 : This simple expression neglects the effects of switch and coil
resistance. This is taken into account in the “Inductor Selection” section.
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