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参数资料
| 型号： | LTC3611IWP#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 10A 64QFN |
| 标准包装： | 2,000 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 32 V |
| 输入电压： | 4.5 V ~ 32 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 10A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 64-VFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 64-QFN（9x9） |
LTC3611
OPERATION
Main Control Loop
The LTC3611 is a high ef ?ciency monolithic synchronous,
step-down DC/DC converter utilizing a constant on-time,
current mode architecture. It operates from an input voltage
range of 4.5V to 32V and provides a regulated output voltage
at up to 10A of output current. The internal synchronous
power switch increases ef ?ciency and eliminates the need
for an external Schottky diode. In normal operation, the
top MOSFET is turned on for a ?xed interval determined
by a one-shot timer OST. When the top MOSFET is turned
off, the bottom MOSFET is turned on until the current
comparator I CMP trips, restarting the one-shot timer and
initiating the next cycle. Inductor current is determined
by sensing the voltage between the PGND and SW pins
using the bottom MOSFET on-resistance. The voltage on
the I TH pin sets the comparator threshold corresponding
to inductor valley current. The error ampli?er, EA, adjusts
this voltage by comparing the feedback signal V FB from
the output voltage with an internal 0.6V reference. If the
load current increases, it causes a drop in the feedback
voltage relative to the reference. The I TH voltage then
rises until the average inductor current again matches
the load current.
At light load, the inductor current can drop to zero and
become negative. This is detected by current reversal
comparator I REV which then shuts off M2 (see Func-
tional Diagram), resulting in discontinuous operation. Both
switches will remain off with the output capacitor supplying
the load current until the I TH voltage rises above the zero
current level (0.8V) to initiate another cycle. Discontinu-
ous mode operation is disabled by comparator F when
the FCB pin is brought below 0.6V, forcing continuous
synchronous operation.
The operating frequency is determined implicitly by the
top MOSFET on-time and the duty cycle required to main-
tain regulation. The one-shot timer generates an on-time
that is proportional to the ideal duty cycle, thus holding
frequency approximately constant with changes in V IN .
The nominal frequency can be adjusted with an external
resistor, R ON .
Overvoltage and undervoltage comparators OV and UV
pull the PGOOD output low if the output feedback volt-
age exits a ±10% window around the regulation point.
Furthermore, in an overvoltage condition, M1 is turned
off and M2 is turned on and held on until the overvoltage
condition clears.
Foldback current limiting is provided if the output is
shorted to ground. As V FB drops, the buffered current
threshold voltage I THB is pulled down by clamp Q3 to
a 1V level set by Q4 and Q6. This reduces the inductor
valley current level to one sixth of its maximum value as
V FB approaches 0V.
Pulling the RUN/SS pin low forces the controller into its
shutdown state, turning off both M1 and M2. Releasing
the pin allows an internal 1.2μA current source to charge
up an external soft-start capacitor, C SS . When this voltage
reaches 1.5V, the controller turns on and begins switching,
but with the I TH voltage clamped at approximately 0.6V
below the RUN/SS voltage. As C SS continues to charge,
the soft-start current limit is removed.
INTV CC /EXTV CC Power
Power for the top and bottom MOSFET drivers and most of
the internal controller circuitry is derived from the INTV CC
pin. The top MOSFET driver is powered from a ?oating
bootstrap capacitor, C B . This capacitor is recharged from
INTV CC through an external Schottky diode, D B , when
the top MOSFET is turned off. When the EXTV CC pin is
grounded, an internal 5V low dropout regulator supplies
the INTV CC power from V IN . If EXTV CC rises above 4.7V,
the internal regulator is turned off, and an internal switch
connects EXTV CC to INTV CC . This allows a high ef ?ciency
source connected to EXTV CC , such as an external 5V sup-
ply or a secondary output from the converter, to provide
the INTV CC power. Voltages up to 7V can be applied to
EXTV CC for additional gate drive. If the input voltage is
low and INTV CC drops below 3.5V, undervoltage lockout
circuitry prevents the power switches from turning on.
3611fd
0
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