參數(shù)資料
型號(hào)： LT1938IDD#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： 4 A SWITCHING REGULATOR, 3300 kHz SWITCHING FREQ-MAX, PDSO10
封裝： 3 X 3 MM, LEAD FREE, PLASTIC, MO-229WEED-2, DFN-10
文件頁(yè)數(shù)： 5/24頁(yè)
文件大?。?/td> 260K
代理商： LT1938IDD#PBF
LT1938
13
1938fa
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
electrolyticcapacitorscanbeusedfortheoutputcapacitor.
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.
Catch Diode
The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:
ID(AVG) = IOUT (VIN – VOUT)/VIN
where IOUT is the output load current. The only reason to
consideradiodewithalargercurrentratingthannecessary
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.
Table 3. Diode Vendors
PART NUMBER
VR
(V)
IAVE
(A)
VF AT 1A
(mV)
VF AT 2A
(mV)
On Semiconductor
MBRM120E
20
1
530
595
Diodes Inc.
B120
B130
B220
B230
DFLS230L
20
30
20
30
1
2
500
International Rectifier
10BQ030
20BQ030
30
1
2
420
470
Frequency Compensation
The LT1938 uses current mode control to regulate the
output.Thissimplifiesloopcompensation.Inparticular,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
VC pin, as shown in Figure 2. Generally a capacitor (CC)
and a resistor (RC) in series to ground are used. In addi-
tion, there may be lower value capacitor in parallel. This
capacitor (CF) 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.
VENDOR
PHONE
URL
PART SERIES
COMMANDS
Panasonic
(714) 373-7366
www.panasonic.com
Ceramic,
Polymer,
Tantalum
EEF Series
Kemet
(864) 963-6300
www.kemet.com
Ceramic,
Tantalum
T494, T495
Sanyo
(408) 749-9714
www.sanyovideo.com
Ceramic,
Polymer,
Tantalum
POSCAP
Murata
(408) 436-1300
www.murata.com
Ceramic
AVX
www.avxcorp.com
Ceramic,
Tantalum
TPS Series
Taiyo Yuden
(864) 963-6300
www.taiyo-yuden.com
Ceramic
Table 2. Capacitor Vendors
APPLICATIONS INFORMATION
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