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参数资料
| 型号： | LT1941EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG TRPL 28TSSOP |
| 标准包装： | 2,000 |
| 类型： | 降压（降压），升压（升压），反相，Sepic |
| 输出类型： | 可调式 |
| 输出数： | 3 |
| 输出电压： | 1.25 V ~ 40 V |
| 输入电压： | 3.5 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.1MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
LT1941
APPLICATIONS INFORMATION
Converter with Backup Output Regulator
There is another situation to consider in systems where the
output will be held high when the input to the LT1941 is
absent. If the V IN and one of the RUN/SS pins are allowed
to ?oat, then the LT1941’s internal circuitry will pull its
quiescent current through its SW pin. This is acceptable if
Regulating Negative Output Voltages
The LT1941 contains an inverting op-amp with its nonin-
verting terminal tied to ground and its output connected
to the FB3 pin. Use this op-amp to generate a voltage at
FB3 that is proportional to V OUT . Choose the resistors
according to:
the system can tolerate a few mA of load in this state. With
both RUN/SS pins grounded, the LT1941 enters shutdown
mode and the SW pin current drops to ~50mA. However, if
the V IN pin is grounded while the output is held high, then
parasitic diodes inside the LT1941 can pull large currents
R 4 =
R 3 ? V OUT
1 . 24 V
–V OUT
from the output through the SW pin and the V IN pin. A
Schottky diode in series with the input to the LT1941, as
shown in Figure 4, will protect the LT1941 and the system
from a shorted or reversed input.
R4
R3
NFB
FB3
1941 AI02
PARASITIC DIODE
Use 10k or larger, up to 20k for R3.
V IN
D4
V IN
SW
V OUT
Duty Cycle Range
LT1941
1941 F04
The maximum duty cycle (DC) of the LT1941 inverter/boost
regulator is 77%. The duty cycle for a given application
using the inverting topology is:
Figure 4. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output
DC =
V OUT
V IN + V OUT
DC = OUT IN
R 3 = R 4 ? OUT – 1 ?
INVERTER/BOOST CONSIDERATIONS
Regulating Positive Output Voltages
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistors
according to:
? V ?
? 1 . 25 V ?
R4 should be 10k or less to avoid bias current errors.
NFB should be tied to FB3.
V OUT
The duty cycle for a given application using the boost
topology is:
V – V
V OUT
The LT1941 can still be used in applications where the
DC, as calculated above, is above 77%; however, the part
must be operated in discontinuous mode so that the actual
duty cycle is reduced.
Inductor Selection
Several inductors that work well with the LT1941 inverter/
boost regulator are listed in Table 4. Besides these, many
R3
R4
FB3
other inductors will work. Consult each manufacturer
for detailed information and for their entire selection of
related parts. Use ferrite core inductors to obtain the best
ef?ciency. When using coupled inductors, choose one that
1941 AI01
1941fb
14
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