参数资料
型号: LT3433EFE#TRPBF
厂商: Linear Technology
文件页数: 10/16页
文件大小: 0K
描述: IC REG BUCK BST ADJ 0.5A 16TSSOP
标准包装: 2,500
类型: 降压(降压),升压(升压)
输出类型: 可调式
输出数: 1
输出电压: 3.3 V ~ 20 V
输入电压: 4 V ~ 60 V
PWM 型: 电流模式,混合
频率 - 开关: 200kHz
电流 - 输出: 500mA
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 16-TSSOP-EP
LT3433
APPLICATIO S I FOR ATIO
The requirement for avoiding current mode instability is
that the rising slope of sensed inductor ripple current (S1)
is greater than the falling slope (S2). At duty cycles greater
than 50% this is not true. To avoid the instability condition,
a false signal is added to the sensed current with a slope
(S X ) that is sufficient to prevent current mode instability,
or S1 + S X ≥ S2. This leads to the following relations:
S X ≥ S2(2DC – 1)/DC
If the forward voltages of a converter’s catch and pass
diodes are defined as V F1 and V F2 , then:
S2 = (V OUT + V F1 + V F2 )/L
Solving for L yields a relation for the minimum inductance
that will satisfy slope compensation requirements:
L MIN = (V OUT + V F1 + V F2 )(2DC – 1)/(DC ? S X )
The LT3433 maximizes available dynamic range using a
slope compensation generator that generates a continu-
ously increasing slope as duty cycle increases. The slope
compensation waveform is calibrated at 80% duty cycle to
generate an equivalent slope of at least 0.05A/ μ s. The
Converter Capabilities
The output current capability of an LT3433 converter is
affected by a myriad of variables. The current in the
switches is limited by the LT3433. Switch current is
measured coming from the V IN supply, and does not
directly translate to a limitation in load current. This is
especially true during bridged mode operation when the
converter output current is discontinuous.
During bridged mode operation, the converter output
current is discontinuous, or only flowing to the output
while the switches are off (not to be confused with discon-
tinuous switcher operation). As a result, the maximum
output current capability of the converter is reduced from
that during buck mode operation by a factor of roughly
1 – DC, not including additional losses. Most converter
losses are also a function of DC, so operational duty cycle
must be accurately determined to predict converter load
capabilities.
V IN
equation for minimum inductance then reduces to:
SW_H
L MIN = (V OUT + V F1 + V F2 )(15e-6)
For example, with V OUT = 5V and using V F1 + V F2 = 1.1V
LT3433
SW_L
L
D2
D1
V OUT
(cold):
L MIN = (5 + 1.1)(15e-6) = 91.5 μ H
Slope Compensation Requirements
Typical Minimum Inductor Values vs V OUT
350
300
250
200
150
3433 AI02
Application variables:
V IN = Converter input supply voltage
V OUT = Converter programmed output voltage
V BST = Boosted supply voltage (V BST – V SWH )
DC = Operational duty cycle
f O = Switching frequency
I MAX = Peak switch current limit
? I L = Inductor ripple current
100
50
4
6
8
10
12
V OUT (V)
14
16
18
20
I SW = Average switch current or peak switch current
less half the ripple current (I MAX – ? I L /2)
R SWH = Boosted switch “on” resistance
3433 AI01
R SWL = Grounded switch “on” resistance
L = Inductor value
3433f
10
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