参数资料
型号: LTC3839EUH#PBF
厂商: Linear Technology
文件页数: 29/50页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 32-QFN
标准包装: 73
系列: PolyPhase®
PWM 型: 电流模式
输出数: 1
频率 - 最大: 2MHz
电源电压: 4.5 V ~ 38 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 32-WFQFN 裸露焊盘
包装: 管件
LTC3839
APPLICATIONS INFORMATION
to INTV CC , it will operate in forced continuous mode at
the R T -programmed frequency. If the MODE/PLLIN pin is
tied to SGND, the LTC3839 will operate in discontinuous
mode at light load and switch into continuous conduction
at the R T programmed frequency as load increases. The TG
on-time during discontinuous conduction is intentionally
slightly extended (approximately 1.2 times the continuous
conduction on-time as calculated from V IN , V OUT and f) to
create hysteresis at the load-current boundary of continu-
ous/discontinuous conduction.
If an application requires very low (approaching minimum)
on-time, the system may not be able to maintain its full
frequency synchronization range. Getting closer to mini-
mum on-time, it may even lose phase/frequency lock at no
load or light load conditions, under which the SW on-time
is effectively longer than TG on-time due to TG/BG dead
times. This is discussed further under Minimum On-Time,
Minimum Off-Time and Dropout Operation.
I LOAD
CLOCK
INPUT
Minimum On-Time, Minimum Off-Time
and Dropout Operation
The minimum on-time is the smallest duration that
LTC3839’s TG (top gate) pin can be in high or “on” state.
It has dependency on the operating conditions of the
switching regulator, and is a function of voltages on the
V IN and V OUT pins, as well as the value of external resistor
R T . A minimum on-time of 30ns can be achieved when the
V OUT pin is tied to its minimum value of 0.6V while the V IN
is tied to its maximum value of 38V. For larger values of
V OUT and/or smaller values of V IN , the minimum achievable
on-time will be longer. The valley mode control architecture
allows low on-time, making the LTC3839 suitable for high
step-down ratio applications.
The effective on-time, as determined by the SW node
pulse width, can be different from this TG on-time, as it
also depends on external components, as well as loading
PHASE AND
FREQUENCY
LOCKED
PHASE AND
FREQUENCY
LOCK LOST
FREQUENCY
RESTORED
QUICKLY
PHASE LOCK
RESUMED
PHASE AND
FREQUENCY
LOCK LOST
FREQUENCY
RESTORED
QUICKLY
SW
V OUT
DUE TO FAST
LOAD STEP
DUE TO FAST
LOAD STEP
3839 F10
Figure 10. Phase and Frequency Locking Behavior During Transient Conditions
3839fa
29
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