参数资料
型号: LT1938EDD#TRPBF
厂商: Linear Technology
文件页数: 13/24页
文件大小: 0K
描述: IC REG BUCK ADJ 2.2A 10DFN
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 1.27 V ~ 20 V
输入电压: 3.6 V ~ 25 V
PWM 型: 电流模式
频率 - 开关: 300kHz ~ 2.8MHz
电流 - 输出: 2.2A
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: 10-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 10-DFN(3x3)
LT1938
APPLICATIONS INFORMATION
Table 2. Capacito r Vendors
VENDOR
Panasonic
PHONE
(714) 373-7366
URL
www.panasonic.com
PART SERIES
Ceramic,
COMMANDS
Polymer,
Tantalum
EEF Series
Kemet
Sanyo
(864) 963-6300
(408) 749-9714
www.kemet.com
www.sanyovideo.com
Ceramic,
Tantalum
Ceramic,
Polymer,
T494, T495
POSCAP
Tantalum
Murata
AVX
Taiyo Yuden
(408) 436-1300
(864) 963-6300
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
Ceramic
Ceramic,
Tantalum
Ceramic
TPS Series
When choosing a capacitor, look carefully through the
data sheet to find out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor, or one with a higher voltage
rating, may be required. High performance tantalum or
electrolytic capacitors can be used for the output capacitor.
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specified
by the supplier, and should be 0.05Ω or less. Such a
capacitor will be larger than a ceramic capacitor and will
have a larger capacitance, because the capacitor must be
large to achieve low ESR. Table 2 lists several capacitor
vendors.
Table 3. Diode Vendors
V R
PART NUMBER (V)
On Semiconductor
MBRM120E 20
Diodes Inc.
B120 20
B130 30
B220 20
B230 30
DFLS230L 30
International Rectifier
10BQ030 30
20BQ030 30
Frequency Compensation
I AVE
(A)
1
1
1
2
2
2
1
2
V F AT 1A
(mV)
530
500
500
420
V F AT 2A
(mV)
595
500
500
500
470
470
Catch Diode
The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:
I D(AVG) = I OUT (V IN – V OUT )/V IN
where I OUT is the output load current. The only reason to
consider a diode with a larger current rating than necessary
for nominal operation is for the worst-case condition of
shorted output. The diode current will then increase to the
typical peak switch current. Peak reverse voltage is equal
to the regulator input voltage. Use a diode with a reverse
voltage rating greater than the input voltage. Table 3 lists
several Schottky diodes and their manufacturers.
The LT1938 uses current mode control to regulate the
output. This simplifies loop compensation. In particular, the
LT1938 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
compensation is provided by the components tied to the
V C pin, as shown in Figure 2. Generally a capacitor (C C )
and a resistor (R C ) in series to ground are used. In addi-
tion, there may be lower value capacitor in parallel. This
capacitor (C F ) is not part of the loop compensation but
is used to filter noise at the switching frequency, and is
required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.
1938fa
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