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参数资料
| 型号： | LT3508IUF#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封装： | 4 X 4 MM, PLASTIC, MO-220WGGD-X, QFN-24 |
| 文件页数： | 3/24页 |
| 文件大小： | 365K |
| 代理商： | LT3508IUF#TR |
LT3508
11
3508f
rule above, then the maximum load current will depend
on input voltage. In addition, low inductance may result
in discontinuous mode operation, which further reduces
maximum load current. For details of maximum output
current and discontinuous mode operation, see Linear
Technology’s Application Note 44. Finally, for duty cycles
greater than 50% (VOUT/VIN > 0.5), a minimum inductance
is required to avoid sub-harmonic oscillations:
LV
V
kHz
f
MIN
OUT
F
=+
()
800
The current in the inductor is a triangle wave with an average
value equal to the load current. The peak switch current
is equal to the output current plus half the peak-to-peak
inductor ripple current. The LT3508 limits its switch cur-
rent in order to protect itself and the system from overload
faults. Therefore, the maximum output current that the
LT3508 will deliver depends on the switch current limit,
the inductor value, and the input and output voltages.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
I
DC V
V
Lf
L
OUT
F
= ()
+
()
1–
where f is the switching frequency of the LT3508 and L
is the value of the inductor. The peak inductor and switch
current is:
II
I
SW PK
L PK
OUT
L
()
==
+
2
To maintain output regulation, this peak current must be
less than the LT3508’s switch current limit ILIM. ILIM is
at least 2A for at low duty cycles and decreases linearly
to 1.55A at DC = 90%. The maximum output current is a
function of the chosen inductor value:
II
I
ADC
I
OUT MAX
LIM
LL
()
–
– .
–
==
()
2
21 0 25
2
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors,
and choose one to meet cost or space goals. Then use
these equations to check that the LT3508 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continu-
ous. Discontinuous operation occurs when IOUT is less
than
ΔIL/2.
Input Capacitor Selection
Bypass the VIN pins of the LT3508 circuit with a ceramic
capacitor of X7R or X5R type. For switching frequencies
above 500kHz, use a 4.7F capacitor or greater. For switch-
ing frequencies below 500kHz, use a 10F or higher capaci-
tor. If the VIN pins are tied together only a single capacitor
is necessary. If the VIN pins are separated, each pin will
need its own bypass. The following paragraphs describe
the input capacitor considerations in more detail.
Step-down regulators draw current from the input supply
in pulses with very fast rise and fall times. The input ca-
pacitor is required to reduce the resulting voltage ripple at
the LT3508 input and to force this switching current into a
tight local loop, minimizing EMI. The input capacitor must
have low impedance at the switching frequency to do this
effectively, and it must have an adequate ripple current
rating. With two switchers operating at the same frequency
but with different phases and duty cycles, calculating the
input capacitor RMS current is not simple. However, a
conservative value is the RMS input current for the channel
that is delivering most power (VOUT times IOUT):
CI
VV
V
I
IN RMS
OUT
IN
OUT
IN
OUT
()
–
=
()
<
2
and is largest when VIN = 2VOUT (50% duty cycle). As
the second, lower power channel draws input current,
the input capacitor’s RMS current actually decreases as
the out-of-phase current cancels the current drawn by
the higher power channel. Considering that the maximum
load current from a single channel is ~1.4A, RMS ripple
current will always be less than 0.7A.
APPLICATIONS INFORMATION
相关PDF资料 |
PDF描述 |
|---|---|
| LT3508IUF | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
| LT3508IFE#TR | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3508EUF | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
| LT3509HMSE#TRPBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3509IMSE#PBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
相关代理商/技术参数 |
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|---|---|
| LT3508IUF-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic 1.4A Step-Down Switching Regulator |
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| LT3509EDE#PBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 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:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT3509EDE#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 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:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3509EDEPBF | 制造商:Linear Technology 功能描述:Sw. Regulator Dual 700mA 3.6-36V DFN14EP |
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