参数资料
型号: LT3434IFE
厂商: Linear Technology
文件页数: 9/24页
文件大小: 0K
描述: IC REG BUCK ADJ 3A 16TSSOP
标准包装: 95
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 1.25 V ~ 54 V
输入电压: 3.3 V ~ 60 V
PWM 型: 电流模式,混合
频率 - 开关: 200kHz
电流 - 输出: 3A
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: 管件
供应商设备封装: 16-TSSOP-EP
LT3434
BLOCK DIAGRA
power from the V IN pin, but if the BIAS pin is connected to
an external voltage higher than 3V bias power will be
drawn from the external source (typically the regulated
output voltage). This improves efficiency.
High switch efficiency is attained by using the BOOST pin
to provide a voltage to the switch driver which is higher
than the input voltage, allowing switch to be saturated.
This boosted voltage is generated with an external capaci-
tor and diode.
APPLICATIO S I FOR ATIO
FEEDBACK PIN FUNCTIONS
To further optimize efficiency, the LT3434 automatically
switches to Burst Mode operation in light load situations.
In Burst Mode operation, all circuitry associated with
controlling the output switch is shut down reducing the
input supply current to 45 μ A.
The LT3434 contains a power good flag with a program-
mable threshold and delay time. A logic-level low on the
SHDN pin disables the IC and reduces input suppy current
to less than 1 μ A.
Table 1
The feedback (FB) pin on the LT3434 is used to set output
voltage and provide several overload protection features.
The first part of this section deals with selecting resistors
to set output voltage and the remaining part talks about
frequency foldback and soft-start features. Please read
both parts before committing to a final design.
Referring to Figure 2, the output voltage is determined by
a voltage divider from V OUT to ground which generates
1.25V at the FB pin. Since the output divider is a load on the
output care must be taken when choosing the resistor
OUTPUT
VOLTAGE
(V)
2.5
3
3.3
5
6
8
10
12
R2
(k ? , 1%)
100
100
100
100
100
100
100
100
R1
NEAREST (1%)
(k ? )
100
140
165
300
383
536
698
866
OUTPUT
ERROR
(%)
0
0
0.38
0
0.63
– 0.63
– 0.25
0.63
divider values. For light load applications the resistor
values should be as large as possible to achieve peak
efficiency in Burst Mode operation. Extremely large values
for resistor R1 will cause an output voltage error due to the
LT3434
SW 2
V OUT
50nA FB pin input current. The suggested value for the
output divider resistor (see Figure 2) from FB to ground
SOFT-START
C SS
9
C1
(R2) is 100k or less. A formula for R1 is shown below. A
table of standard 1% values is shown in Table 1 for
common output voltages.
200kHz
OSCILLATOR
FOLDBACK
DETECT
R1
R 1 = R 2 ?
V OUT – 1 . 25
1 . 25 + R 2 ? 50 nA
ERROR
AMP
+
FB
12
R2
More Than Just Voltage Feedback
1.25V
The FB pin is used for more than just output voltage
sensing. It also reduces switching frequency and con-
trols the soft-start voltage ramp rate when output voltage
is below the regulated level (see the Frequency Foldback
V C
Figure 2. Feedback Network
11
3434 F02
3434fb
9
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