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参数资料
| 型号： | LTC3873ETS8#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK TSOT23-8 |
| 标准包装： | 500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 240kHz |
| 占空比： | 84% |
| 电源电压： | 8.8 V ~ 75 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | SOT-23-8 薄型，TSOT-23-8 |
| 包装： | 带卷 (TR) |
LTC3873
APPLICATIONS INFORMATION
V CC + V D 2
N BIAS = N SEC
V CC Bias Power
The V CC pin must be bypassed to the GND pin with a
minimum 10μF ceramic or tantalum capacitor located
immediately adjacent to the two pins. Proper supply by-
passing is necessary to supply the high transient currents
required by the MOSFET gate driver.
For maximum ?exibility, the LTC3873 is designed so
that it can be operated from voltages well beyond the
LTC3873’s absolute maximum ratings. In the simplest case,
the LTC3873 can be powered with a resistor connected
between the input voltage and V CC . The built-in shunt
regulator limits the voltage on the V CC pin to around 9.3V
as long as the shunt regulator is not forced to sink more
than 25mA. This powering scheme has the drawback that
the power loss in the resistor reduces converter ef?ciency
and the 25mA shunt regulator maximum may limit the
maximum-minimum range of input voltage.
In some cases, the input or the output voltage is within
the operational range of V CC for the LTC3873. In this case,
the LTC3873 is operated directly from either the input or
output voltage. The typical application circuit on the ?rst
page of this data sheet shows a 5V output converter in
which R START and C VCC form a start-up trickle charger while
D1 powers V CC from the output once the converter is in
normal operation. Note that R START need only supply the
very small 55μA micropower start-up current while C VCC
is charged to V TURNON . At this point, V RUN/SS > V SHDN ,
additional bias winding to provide bias power. Note that this
topology is very powerful because, by appropriate choice
of the transformer turn ratio, the output voltage can be
chosen without regard to the value of the input voltage or
the V CC bias power for the LTC3873. The number of the
turns in the bias winding is chosen according to:
V OUT + V D 1
where N BIAS is the number of turns in the bias winding,
N SEC is the number of turns in the secondary winding,
V CC is the desired voltage to power the LTC3873, V OUT
is the converter output voltage, V D1 is the forward drop
voltage of D1 and V D2 is the forward drop voltage of D2.
Note that since V OUT is regulated by the converter control
loop, V CC is also regulated although not precisely. The
value of V CC is often constrained since N BIAS and N SEC are
often a limited range of small integer numbers. For proper
operation, the value of V CC must be between V TURNON and
V TURNOFF . Since the ratio of V TURNON to V TURNOFF is over
two to one, the requirement is relative easy to satisfy.
Finally, as with all trickle charger start-up schemes, the
soft-start must be fast enough so that the power supplied
by the bias winding is available before the discharge of
C VCC down to V TURNOFF .
T1
the converter begins switching the external MOSFET and
ramps up the converter output voltage at a rate set by the
D2
V IN
N BIAS
?
D1
capacitor C RUN/SS on the RUN/SS pin. Since R START cannot
supply enough current to operate the external MOSFET, C VCC
begins discharging and V CC drops. The soft-start must be
R3
R START
C IN
N PRI
?
?
N SEC
C OUT
V OUT
fast enough so that the output voltage reaches its target
value of 5V before V CC drops to V TURNOFF or the converter
will fail to start. Otherwise more C VCC capacitor is needed
C VCC
C VIN
V CC
RUN/SS NGATE
LTC3873
Q1
to hold the input voltage when soft-start is too long.
Figure 5 shows a different ?yback converter bias power
C C
I TH
GND
SW
R SL
R SENSE
strategy for a case in which neither the input or the output
V FB
is suitable for providing the bias power to the LTC3873.
R1
R2
3873 F05
The trickle charger is identical to that described in the
prior paragraph. However, the ?yback transformer has an
Figure 5. Typical LTC3873 Application Circuit
3873fa
9
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3873IDDB-5#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Isolated, Cut Tape No Rsense Constant Frequency Current Mode Boost/Flyb |
| LTC3873IDDB-5#TRMPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 8-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3873IDDB-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 8-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3873ITS8-5#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Isolated, Cut Tape No Rsense Constant Frequency Current Mode Boost/Flyb |
| LTC3873ITS8-5#TRMPBF | 功能描述:IC REG CTRLR BST FLYBK TSOT23-8 RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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