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参数资料
| 型号： | LTC3810EG |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO28 |
| 封装： | 5.30 MM, PLASTIC, SSOP-28 |
| 文件页数： | 4/36页 |
| 文件大小： | 495K |
| 代理商： | LTC3810EG |
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LTC3810
12
3810fb
Main Control Loop
The LTC3810 is a current mode controller for DC/DC step-
down converters. 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 bot-
tom MOSFET is turned on until the current comparator
ICMP trips, restarting the one-shot timer and initiating the
next cycle. Inductor current is determined by sensing the
voltage between the SENSE– and SENSE+ pins using a
sense resistor or the bottom MOSFET on-resistance. The
voltage on the ITH pin sets the comparator threshold cor-
responding to the inductor valley current. The fast 25MHz
error amplier EA adjusts this voltage by comparing the
feedback signal VFB to the internal 0.8V reference volt-
age. If the load current increases, it causes a drop in the
feedback voltage relative to the reference. The ITH voltage
then rises until the average inductor current again matches
the load current.
The operating frequency is determined implicitly by the top
MOSFET on-time and the duty cycle required to maintain
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 VIN. The nominal
frequency can be adjusted with an external resistor RON.
For applications with stringent constant frequency re-
quirements, the LTC3810 can be synchronized with an
external clock. By programming the nominal frequency
the same as the external clock frequency, the LTC3810
behaves as a constant frequency part against the load and
supply variations.
Pulling the SHDN pin low forces the controller into its
shutdown state, turning off both M1 and M2. Forcing a
voltage above 1.5V will turn on the device.
Pulse Skip Mode
The LTC3810 can operate in one of two modes selectable
with the MODE/SYNC pin—pulse skip mode or forced
continuous mode (see Figure 1). Pulse skip mode is se-
lected when increased efciency at light loads is desired
(see Figure 2). In this mode, the bottom MOSFET is turned
off when inductor current reverses to minimize efciency
loss due to reverse current ow and gate charge switching.
At low load currents, ITH will drop below the zero current
level (1.2V) shutting off both switches. Both switches will
remain off with the output capacitor supplying the load
current until the ITH voltage rises above the zero current
level to initiate another cycle. In this mode, frequency is
proportional to load current at light loads.
Pulse skip mode operation is disabled by comparator F
when the MODE/SYNC pin is brought below 0.8V, forcing
continuous synchronous operation. Forced continuous
mode is less efcient due to resistive losses, but has the
advantage of better transient response at low currents,
approximately constant frequency operation, and the ability
to maintain regulation when sinking current.
Figure 1. Comparison of Inductor Current Waveforms
for Pulse Skip Mode and Forced Continuous Operation
Figure 2. Efciency in Pulse Skip Mode
and Forced Continuous Mode
OPERATION
DECREASING
LOAD
CURRENT
3810 F01
PULSE SKIP MODE
0A
FORCED CONTINUOUS
LOAD (A)
0.01
40
EFFICIENCY
(%)
50
60
70
80
0.1
1
10
30
20
10
0
90
100
3810 F02
VIN = 25V
VIN = 75V
PULSE SKIP MODE
FORCED CONTINUOUS
VIN = 75V
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| LTC3810EG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP 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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