参数资料
型号: LTC3610IWP#PBF
厂商: Linear Technology
文件页数: 11/24页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 12A 64QFN
标准包装: 40
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.6 V ~ 24 V
输入电压: 4 V ~ 24 V
PWM 型: 电流模式
电流 - 输出: 12A
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: 64-VFQFN 裸露焊盘
包装: 管件
供应商设备封装: 64-QFN(9x9)
LTC3610
APPLICATIONS INFORMATION
R ON (k )
1000
100
100
V OUT = 1.5V
V OUT = 3.3V
V OUT = 2.5V
1000 10000
3610 F01a
as current increases, constant frequency operation can be
maintained. This is accomplished with a resistive divider
from the I TH pin to the V ON pin and V OUT . The values
required will depend on the parasitic resistances in the
specific application. A good starting point is to feed about
25% of the voltage change at the I TH pin to the V ON pin
as shown in Figure 2a. Place capacitance on the V ON pin
to filter out the I TH variations at the switching frequency.
The resistor load on I TH reduces the DC gain of the error
amp and degrades load regulation, which can be avoided
by using the PNP emitter follower of Figure 2b.
Figure 1a. Switching Frequency vs R ON  (V ON  = 0V)
1000
V OUT = 12V
V OUT = 5V
V OUT = 3.3V
Minimum Off-Time and Dropout Operation
The minimum off-time, t OFF(MIN), is the smallest amount
of time that the LTC3610 is capable of turning on the bot-
tom MOSFET, tripping the current comparator and turning
the MOSFET back off. This time is generally about 250ns.
The minimum off-time limit imposes a maximum duty
cycle of t ON /(t ON + t OFF(MIN) ). If the maximum duty cycle
is reached, due to a dropping input voltage for example,
then the output will drop out of regulation. The minimum
input voltage to avoid dropout is:
100
100
1000
10000
V IN ( MIN ) = V OUT
t ON + t OFF (MIN)
t ON
R ON (k )
R ON 2 =
R ON
V OUT = 0.6V ? 1 +
3610 F01b
Figure 1b. Switching Frequency vs R ON  (V ON  = INTV CC )
Because the voltage at the I ON pin is about 0.7V, the cur-
rent into this pin is not exactly inversely proportional to
V IN , especially in applications with lower input voltages.
To correct for this error, an additional resistor R ON2 con-
nected from the I ON pin to the 5V INTV CC supply will further
stabilize the frequency.
5 V
0 . 7 V
Changes in the load current magnitude will also cause
frequency shift. Parasitic resistance in the MOSFET
switches and inductor reduce the effective voltage across
the inductance, resulting in increased duty cycle as the
load current increases. By lengthening the on-time slightly
A plot of maximum duty cycle vs frequency is shown in
Figure 3.
Setting the Output Voltage
The LTC3611 develops a 0.6V reference voltage between
the feedback pin, V FB , and the signal ground as shown in
Figure 6. The output voltage is set by a resistive divider
according to the following formula:
? R2 ?
?
? R1 ?
To improve the frequency response, a feedforward capaci-
tor C1 may also be used. Great care should be taken to
route the V FB line away from noise sources, such as the
inductor or the SW trace.
3610ff
  
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