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参数资料
| 型号： | LTC3548IMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ DL 10MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.6 V ~ 5 V |
| 输入电压： | 2.5 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 2.25MHz |
| 电流 - 输出： | 400mA，800mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 10-MSOP 裸露焊盘 |
LTC3548
APPLICATIONS INFORMATION
stray capacitance to cause noise problems and reduce the
phase margin of the error amp loop.
To improve the frequency response, a feed-forward capaci-
tor C F may also be used. Great care should be taken to
route the V FB line away from noise sources, such as the
inductor or the SW line.
Power-On Reset
The POR pin is an open-drain output which pulls low when
either regulator is out of regulation. When both output volt-
ages are above –8.5% of regulation, a timer is started which
releases POR after 2 18 clock cycles (about 117ms). This
delay can be signi?cantly longer in Burst Mode operation
with low load currents, since the clock cycles only occur
during a burst and there could be milliseconds of time
between bursts. This can be bypassed by tying the POR
output to the MODE/SYNC input, to force pulse-skipping
mode during a reset. In addition, if the output voltage faults
during Burst Mode sleep, POR could have a slight delay for
an undervoltage output condition. This can be avoided by
using pulse-skipping mode instead. When either channel
is shut down, the POR output is pulled low, since one or
both of the channels are not in regulation.
Mode Selection and Frequency Synchronization
The MODE/SYNC pin is a multipurpose pin which provides
mode selection and frequency synchronization. Connect-
ing this pin to V IN enables Burst Mode operation, which
provides the best low current ef?ciency at the cost of a
higher output voltage ripple. Connecting this pin to ground
selects pulse-skipping mode, which provides the lowest
output ripple, at the cost of low current ef?ciency.
The LTC3548 can also be synchronized to another LTC3548
by the MODE/SYNC pin. During synchronization, the mode
is set to pulse-skipping and the top switch turn-on is syn-
chronized to the rising edge of the external clock.
Checking Transient Response
The regulator loop response can be checked by look-
ing 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 ΔI LOAD ? ESR, where ESR is the effective
series resistance of C OUT . ΔI LOAD also begins to charge
or discharge C OUT , generating a feedback error signal
used by the regulator to return V OUT to its steady-state
value. During this recovery time, V OUT can be monitored
for overshoot or ringing that would indicate a stability
problem.
The initial output voltage step may not be within the
bandwidth of the feedback loop, so the standard second-
order overshoot/DC ratio cannot be used to determine
phase margin. In addition, a feed-forward capacitor, C F ,
can be added to improve the high frequency response, as
shown in Figure 2. Capacitor C F provides phase lead by
creating a high frequency zero with R2, which improves
the phase margin.
The output voltage settling behavior is related to the stability
of the closed-loop system and will demonstrate the actual
overall supply performance. For a detailed explanation of
optimizing the compensation components, including a re-
view of control loop theory, refer to Application Note 76.
In some applications, a more severe transient can be
caused by switching loads with large (>1μF) load input
capacitors. The discharged load input capacitors are ef-
fectively 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 switch connecting the load
has low resistance and is driven quickly. The solution
is to limit the turn-on speed of the load switch driver. A
Hot Swap? controller is designed speci?cally for this
purpose and usually incorporates current limiting, short-
circuit protection, and soft-starting.
Ef?ciency Considerations
The percent ef?ciency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the ef?ciency and which change would
produce the most improvement. Percent ef?ciency can
be expressed as:
% Ef?ciency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of
Hot Swap is a trademark of Linear Technology Corporation.
3548fc
10
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| LTC3548IMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Synchronous, 400mA/800mA, 2.25MHz Step-Down DC/DC Regulator |
| LTC3549 | 制造商:LINER 制造商全称:Linear Technology 功能描述:250mA Low VIN Buck Regulator in 2mm × 3mm DFN |
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| LTC3549EDCB#PBF | 制造商:Linear Technology 功能描述:VOLTAGE REGULATOR BUCK 2.25M 制造商:Linear Technology 功能描述:VOLTAGE REGULATOR, BUCK, 2.25MHZ, 250mA, DFN-6; Primary Input Voltage:5.5V; No. of Outputs:1; Output Current:250mA; No. of Pins:6; Operating Temperature Min:-40C; Operating Temperature Max:85C; Package / Case:6-DFN ;RoHS Compliant: Yes |
| LTC3549EDCB#TRM | 制造商:Linear Technology 功能描述:250MA, LOW VIN BUCK REGULATOR |
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