参数资料
型号: LT3724MPFE#PBF
厂商: Linear Technology
文件页数: 11/26页
文件大小: 0K
描述: IC REG CTRLR BST INV PWM 16TSSOP
标准包装: 95
PWM 型: 电流模式
输出数: 1
频率 - 最大: 225kHz
占空比: 100%
电源电压: 4 V ~ 60 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -55°C ~ 125°C
封装/外壳: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 管件
LT3724
OPERATIONS
(Refer to Functional Diagram)
Soft-Start
The soft-start function controls the slew rate of the power
supply output voltage during start-up. A controlled output
voltage ramp minimizes output voltage overshoot, reduces
inrush current from the V IN supply, and facilitates supply
sequencing. A capacitor, C SS , connected between V OUT of
the supply and the C SS pin of the IC, programs the slew
rate. The capacitor provides a current to the C SS pin which
is proportional to the dV/dt of the output voltage. The
soft-start circuit overrides the control loop and adjusts the
inductor current until the output voltage slew rate yields a
2μA current through the soft-start capacitor. If the current is
greater than 2μA, then the current threshold set by the DC
control voltage, V C , is decreased and the inductor current
is lowered. This in turn lowers the output current and the
output voltage slew rate is decreased. If the current is less
than 2μA, then the current threshold set by the DC control
voltage, V C , is increased and the inductor current is raised.
This in turn increases the output current and the output
voltage slew rate is increased. Once the output voltage is
within 5% of its regulation voltage, the soft-start circuit
is disabled and the main control regulates the output. The
soft-start circuit is reactivated when the output voltage
drops below 70% of its regulation voltage.
Slope/Antislope Compensation
The IC incorporates slope compensation to eliminate
potential subharmonic oscillations in the current control
loop. The IC’s slope compensation circuit imposes an
artificial ramp on the sensed current to increase the rising
slope as duty cycle increases.
Unfortunately, this additional ramp typically affects the
sensed current value, thereby reducing the achievable
current limit value by the same amount as the added ramp
represents. As such, the current limit is typically reduced
as the duty cycle increases. The LT3724, however, contains
antislope compensation circuitry to eliminate the current
limit reduction associated with slope compensation. As the
slope compensation ramp is added to the sensed current,
a similar ramp is added to the current limit threshold. The
end result is that the current limit is not compromised so
the LT3724 can provide full power regardless of required
duty cycle.
Shutdown
The LT3724 includes a shutdown mode where all the
internal IC functions are disabled and the V IN current is
reduced to less than 10μA. The shutdown pin can be used
for undervoltage lockout with hysteresis, micropower shut-
down or as a general purpose on/off control of the converter
output. The shutdown function has two thresholds. The
first threshold, a precision 1.23V threshold with 120mV
of hysteresis, disables the converter from switching. The
second threshold, approximately a 0.7V referenced to
SGND, completely disables all internal circuitry and reduces
the V IN current to less than 10μA. See the Application
Information section for more information.
3724fd
11
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