参数资料
型号: LTC3813EG#PBF
厂商: Linear Technology
文件页数: 14/32页
文件大小: 0K
描述: IC REG CTRLR BST PWM CM 28-SSOP
标准包装: 47
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: 管件
产品目录页面: 1336 (CN2011-ZH PDF)
LTC3813
APPLICATIONS INFORMATION
Power MOSFET Selection
The LTC3813 requires two external N-channel power
MOSFETs, one for the bottom (main) switch and one for
the top (synchronous) switch. Important parameters for
the power MOSFETs are the breakdown voltage BV DSS ,
threshold voltage V (GS)TH , on-resistance R DS(ON) , Miller
capacitance and maximum current I DS(MAX) .
When the bottom MOSFET is used as the current sense
element, particular attention must be paid to its on-resis-
tance. MOSFET on-resistance is typically speci?ed with
a maximum value R DS(ON)(MAX) at 25°C. In this case,
additional margin is required to accommodate the rise in
MOSFET on-resistance with temperature:
The most important parameter in high voltage applications
is breakdown voltage BV DSS . Both the top and bottom
MOSFETs will see full output voltage plus any additional
ringing on the switch node across its drain-to-source dur-
ing its off-time and must be chosen with the appropriate
breakdown speci?cation. Since most MOSFETs in the 60V
to 100V range have higher thresholds (typically V GS(MIN)
≥ 6V), the LTC3813 is designed to be used with a 6.2V to
14V gate drive supply (DRV CC pin).
For maximum ef?ciency, on-resistance R DS(ON) and input
capacitance should be minimized. Low R DS(ON) minimizes
conduction losses and low input capacitance minimizes
transition losses. MOSFET input capacitance is a combi-
nation of several components but can be taken from the
R DS(ON)(MAX) =
R SENSE
T
typical “gate charge” curve included on most data sheets
(Figure 3).
The ρ T term is a normalization factor (unity at 25°C)
V OUT
accounting for the signi?cant variation in on-resistance
with temperature (see Figure 2) and typically varies
V GS
MILLER EFFECT
V
from 0.4%/°C to 1.0%/°C depending on the particular
MOSFET used.
a b
Q IN
C MILLER = (Q B – Q A )/V DS
+
V GS
+ V
DS
2.0
3813 F03
Figure 3. Gate Charge Characteristic
1.5
The curve is generated by forcing a constant input cur-
1.0
0.5
rent into the gate of a common source, current source
loaded stage and then plotting the gate voltage versus
time. The initial slope is the effect of the gate-to-source
and the gate-to-drain capacitance. The ?at portion of the
curve is the result of the Miller multiplication effect of the
0
–50
0 50 100
JUNCTION TEMPERATURE (°C)
150
3813 F02
drain-to-gate capacitance as the drain drops the voltage
across the current source load. The upper sloping line is
due to the drain-to-gate accumulation capacitance and
Figure 2. R DS(ON) vs Temperature
the gate-to-source capacitance. The Miller charge (the
3813fb
14
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