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参数资料
| 型号： | LTC3521IFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST SYNC ADJ 20TSSOP |
| 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： | 3 |
| 输出电压： | 0.6 V ~ 5.5 V，1.8 V ~ 5.25 V |
| 输入电压： | 1.8 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1.1MHz |
| 电流 - 输出： | 600mA，1A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 20-TSSOP-EP |
LTC3521
APPLICATIONS INFORMATION
V OUT2,3 = 0.6V ? 1 +
R1 ?
?
V OUT1 = 0.6V ? 1 +
R1 ?
?
BuckInputCapacitorSelection
The PV IN2 pin provides current to the buck converter power
switch and is the supply pin for the IC’s internal circuitry.
It is recommended that a low ESR ceramic capacitor with
a value of at least 4.7μF be used to bypass this pin. The
capacitor should be placed as close to the pin as possible
and have a short return to ground.
Buck Output Voltage Programming
The output voltage is set by a resistive divider, according
to the following formula:
? R2 ?
?
The external divider is connected to the output, as shown
in Figure 3. It is recommended that a feedforward capaci-
tor, C FF , be placed in parallel with resistor R2 to improve
the noise immunity of the feedback node. Table 3 provides
the recommended resistor and feedforward capacitor
combinations for common output voltage options.
Table 3. Buck Resistor Divider Values
Buck-Boost Output Voltage Programming
The buck-boost output voltage is set by a resistive divider
according to the following formula:
? R2 ?
?
The external divider is connected to the output, as shown
in Figure 4. The buck-boost converter utilizes voltage
mode control and the value of R2 plays an integral role
in the dynamics of the feedback loop. In general, a larger
value for R2 will increase stability and reduce the speed of
the transient response. A smaller value of R2 will reduce
stability but increase the transient response speed. A good
starting point is to choose R2 = 1MΩ, then calculate the
required value of R1 to set the desired output voltage ac-
cording to the above formula. If a large output capacitor
is used, the bandwidth of the converter is reduced. In
such cases R2 can be reduced to improve the transient
response. If a large inductor or small output capacitor is
utilized, the loop will be less stable and the phase margin
can be improved by increasing the value of R2.
V OUT
0.6V
0.8V
1.0V
1.2V
1.5V
1.8V
2.7V
3.3V
R1
–
200k
118k
100k
78.7k
68.1k
63.4k
60.4k
0.6V ≤ V OUT2 ≤ 5.25V
R2
FB2
R2
0
69.8k
80.6k
102k
121k
137k
226k
274k
0.6V ≤ V OUT3 ≤ 5.25V
R2
FB3
C FF
–
22pF
22pF
22pF
22pF
22pF
33pF
33pF
Buck-Boost Inductor Selection
To achieve high efficiency, a low ESR inductor should
be utilized for the buck-boost converter. The inductor
must have a saturation rating greater than the worst
case average inductor current plus half the ripple current.
The peak-to-peak inductor current ripple will be larger in
buck and boost mode than in the buck-boost region. The
peak-to-peak inductor current ripple for each mode can
1.8V ≤ V OUT1 ≤ 5.25V
R2
FB1
R1
LTC3521
R1
LTC3521
R1
GND
3521 F03
Figure 3. Setting the Buck Output Voltage
GND
3521 F04
Figure 4. Setting the Buck-Boost Output Voltage
15
For more information www.linear.com/LTC3521
3521fb
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