参数资料
型号: LTC3813EG#TRPBF
厂商: Linear Technology
文件页数: 22/32页
文件大小: 0K
描述: IC REG CTRLR BST PWM CM 28-SSOP
标准包装: 2,000
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
电源电压: 7 V ~ 75 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 28-SSOP(0.209",5.30mm 宽)
包装: 带卷 (TR)
LTC3813
APPLICATIONS INFORMATION
=
1 + s ? R ESR ? C OUT
1 + s ? R L ? C OUT
V
L
? OUT 2
Power Dissipation Considerations
Applications using large MOSFETs and high frequency
of operation may result in a large DRV CC /INTV CC supply
current. Therefore, when using the linear regulators, it is
necessary to verify that the resulting power dissipation
is within the maximum limits. The DRV CC /INTV CC supply
current consists of the MOSFET gate current plus the
LTC3813 quiescent current:
H(s) =
V ITH (s) 2.4 ? V OUT ? R DS(ON)
?
? 1 s?
V OUT (s) R L ? V IN ? V SENSE(MAX)
2
R L V IN
(1)
I CC = (f)(Q G(TOP) + Q G(BOTTOM) ) + 3mA
When using the internal LDO regulator, the power dissipa-
tion is internal so the rise in junction temperature can be
estimated from the equation given in Note 2 of the Electrical
Characteristics as follows:
T J = T A + I EXTVCC ? (V EXTVCC – V INTVCC )(100°C/W)
and must not exceed 125°C.
Likewise, if the external NMOS regulator is used, the worst
case power dissipation is calculated to be:
P MOSFET = (V DRAIN(MAX) – 10V) ? I CC
and can be used to properly size the device.
FEEDBACK LOOP/COMPENSATION
Introduction
In a typical LTC3813 circuit, the feedback loop consists of
two sections: the modulator/output stage and the feedback
ampli?er/compensation network. The modulator/output
stage consists of the current sense component and in-
ternal current comparator, the power MOSFET switches
and drivers, and the output ?lter and load. The transfer
function of the modulator/output stage for a boost con-
verter consists of an output capacitor pole, R L C OUT , and
s = j2 f
This portion of the power supply is pretty well out of the
user’s control since the current sense is chosen based on
maximum output load, and the output capacitor is usually
chosen based on load regulation and ripple requirements
without considering AC loop response. The feedback am-
pli?er, on the other hand, gives us a handle on which to
adjust the AC response. The goal is to have an 180° phase
shift at DC so the loop regulates and less than 360° phase
shift at the point where the loop gain falls below 0dB, i.e.,
the crossover frequency, with as much gain as possible
at frequencies below the crossover frequency. Since the
feedback ampli?er adds an additional 90° phase shift to
the phase shift already present from the modulator/output
stage, some phase boost is required at the crossover
frequency to achieve good phase margin. The design
procedure (described in more detail in the next section) is
to (1) obtain a gain/phase plot of modulator/output stage,
(2) choose a crossover frequency and the required phase
boost, and (3) calculate the compensation network.
180
90
GAIN
an ESR zero, R ESR C OUT , and also a “right-half plane” zero,
(R L /L)(V IN 2 / V OUT 2 ). It has a gain/phase curve that is typi-
cally like the curve shown in Figure 10 and is expressed
mathematically in the following equation.
0
PHASE
FREQUENCY (Hz)
0
–90
–180
3813 F10
Figure 10. Bode Plot of Boost Modulator/Output Stage
3813fb
22
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