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参数资料
| 型号： | LTC3772EDDB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-DFN |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 650kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 V |
| 降压： | 是 |
| 升压： | 无 |
| 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 ~ 85°C |
| 封装/外壳： | 8-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
LTC3772
APPLICATIO S I FOR ATIO
To prevent excessive heating in the diode, foldback current
limiting can be added to reduce the current in proportion
to the severity of the fault.
Foldback current limiting is implemented by adding diodes
D FB1 and D FB2 between the output and the I TH /RUN pin as
shown in Figure 4. In a hard short (V OUT = 0V), the current
will be reduced to approximately 50% of the maximum
output current.
and values determine the loop feedback factor gain and
phase. An output current pulse of 20% to 100% of full load
current having a rise time of 1 μ s to 10 μ s will produce
output voltage and I TH pin waveforms that will give a sense
of the overall loop stability. The gain of the loop will be
increased by increasing R C , and the bandwidth of the loop
will be increased by decreasing C C . The output voltage
settling behavior is related to the stability of the closed-
loop system and will demonstrate the actual overall supply
LTC3772
I TH /RUN V FB
R B
R A
D FB1
D FB2
V OUT
performance. For a detailed explanation of optimizing the
compensation components, including a review of control
loop theory, refer to Application Note 76.
A second, more severe transient is caused by switching in
loads with large (>1 μ F) supply bypass capacitors. The
3772 F04
Figure 4. Foldback Current Limiting
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V OUT immediately shifts by an amount
equal to ( ? I LOAD )(ESR), where ESR is the effective series
resistance of COUT . ? I LOAD also begins to charge or dis-
charge C OUT , which generates a feedback error signal. The
regulator loop then returns V OUT to its steady-state value.
During this recovery time, V OUT can be monitored for over-
shoot or ringing. OPTI-LOOP compensation allows the
transient response to be optimized over a wide range of
output capacitance and ESR values.
The I TH series R C -C C filter (see Functional Diagram) sets
discharged bypass capacitors are effectively put in parallel
with C OUT , causing a rapid drop in V OUT . No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25)(C LOAD ).
Thus a 10 μ F capacitor would require a 250 μ s rise time,
limiting the charging current to about 200mA.
Minimum On-Time Considerations
Minimum on-time, t ON(MIN) , is the smallest amount of
time that the LTC3772 is capable of turning the top
MOSFET on and then off. It is determined by internal
timing delays and the gate charge required to turn on the
top MOSFET. The minimum on-time for the LTC3772 is
about 250ns. Low duty cycle and high frequency applica-
tions may approach this minimum on-time limit and care
should be taken to ensure that:
the dominant pole-zero loop compensation. The I TH exter-
nal components shown in the Figure 5 circuit will provide
an adequate starting point for most applications. The
t ON ( MIN ) <
V OUT
f ? V IN
values can be modified slightly (from 0.2 to 5 times their
suggested values) to optimize transient response once the
final PC layout is done and the particular output capacitor
type and value have been determined. The output capaci-
If the duty cycle falls below what can be accommodated by
the minimum on-time, the LTC3772 will begin to skip
cycles. The output voltage will continue to be regulated,
but the ripple current and ripple voltage will increase.
tors need to be decided upon because the various types
3772f
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3772ETS8 | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#PBF | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRM | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM 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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