参数资料
| 型号： | LTC3417EDHC#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ DL 16DFN |
| 标准包装： | 73 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 5 V |
| 输入电压： | 2.25 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1.5MHz，600kHz ~ 4MHz |
| 电流 - 输出： | 800mA，1.4A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-WFDFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 16-DFN（5x3） |
LTC3417
APPLICATIONS INFORMATION
A general LTC3417 application circuit is shown in Figure 4.
External component selection is driven by the load require-
ment, and begins with the selection of the inductors L1
The maximum operating frequency is also constrained
by the minimum on-time and duty cycle. This can be
calculated as:
and L2. Once L1 and L2 are chosen, C IN , C OUT1 and C OUT2
can be selected.
Operating Frequency
f O(MAX) 6.67
V OUT
V IN(MAX)
( MHz )
V OUT V
Selectionoftheoperatingfrequencyisatradeoffbetween
ef?ciency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves ef?ciency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, f O , of the LTC3417 is determined
by pulling the FREQ pin to V IN for 1.5MHz operation or
by connecting an external resistor from FREQ to ground.
The value of the resistor sets the ramp current that is
used to charge and discharge an internal timing capacitor
within the oscillator and can be calculated by using the
following equation:
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of R T .
Inductor Selection
Although the inductor does not in?uence the operating
frequency, the inductor value has a direct effect on ripple
current. The inductor ripple current, Δ I L , decreases with
higher inductance and increases with higher V IN or
V OUT .
I L = 1– OUT
f O ? L V IN
Accepting larger values of Δ I L allows the use of low induc-
tances, but results in higher output voltage ripple, greater
R T =
1.61? 10 11
f O
(
) – 16.586k
core losses and lower output current capability.
A reasonable starting point for setting ripple current is Δ I L =
0.35I LOAD(MAX) , where I LOAD(MAX) is the maximum current
for 0.6MHz ≤ f O ≤ 4MHz. Alternatively, use Figure 1 to
select the value for R T .
160
output. The largest ripple, Δ I L , occurs at the maximum
input voltage. To guarantee that the ripple current stays
below a speci?ed maximum, the inductor value should
be chosen according to the following equation:
140
120
L =
V OUT
f O ? I L
1–
V OUT
V IN(MAX)
100
80
60
40
20
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation begins
when the peak inductor current falls below a level set by the
burst clamp. Lower inductor values result in higher ripple
current which causes this to occur at lower load currents.
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
FREQUENCY (MHz)
3417 F01
This causes a dip in ef?ciency in the upper range of low
current operation. In Burst Mode operation, lower inductor
values will cause the burst frequency to increase.
Figure 1. Frequency vs R T
3417fd
9
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