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| 型号： | LT1110CS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST ADJ 0.4A 8SOIC |
| 标准包装： | 100 |
| 类型： | 降压（降压），升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调 |
| 输入电压： | 1 V ~ 30 V |
| 频率 - 开关： | 70kHz |
| 电流 - 输出： | 400mA |
| 同步整流器： | 无 |
| 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： | 管件 |
| 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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