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參數(shù)資料
| 型號(hào)： | LTC1504CS8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 1 A SWITCHING REGULATOR, 250 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大小： | 249K |
| 代理商： | LTC1504CS8 |
7
LTC1504
EXTERNAL COMPONENT SELECTION
External components required by the LTC1504 fall into
three categories: input bypass, output filtering and com-
pensation. Additional components to set up soft start and
current limit are usually included as well. A minimum
LTC1504 circuit can be constructed with as few as four
external components; a circuit that utilizes all of the
LTC1504s functionality usually includes eight or nine
external components, with two additional feedback resis-
tors required for adjustable parts. See the Typical Applica-
tions section for examples of external component hookup.
Input Bypass
The input bypass capacitor is critical to proper LTC1504
operation. The LTC1504 includes a precision reference
and a pair of high power switches feeding from the same
V
CC
pin. If V
CC
does not have adequate bypassing, the
switch pulses introduce enough ripple at V
CC
to corrupt
the reference voltage and the LTC1504 will not regulate
accurately. Symptoms of inadequate bypassing include
poor load regulation and/or erratic waveforms at the SW
pin. If an oscilloscope won’t trigger cleanly when looking
at the SW pin, there isn’t adequate input bypass.
Ideally, the LTC1504 requires a low impedance bypass
right at the chip and a larger reservoir capacitor that can be
located somewhat farther away. This requirement usually
can be met with a ceramic capacitor right next to the
LTC1504 and an electrolytic capacitor (usually 10
μ
F to
100
μ
F, depending on expected load current) located some-
where nearby. In certain cases, the bulk capacitance
requirement can be met by the output bypass of the input
supply. Applications running at very high load currents or
at input supply voltages greater than 6V may require the
local ceramic capacitor to be 1
μ
F or greater. In some
cases, both the low impedance and bulk capacitance
requirements can be met by a single capacitor, mounted
very close to the LTC1504. Low ESR organic semiconduc-
tor (OS-CON) electrolytic capacitors or surge tested sur-
face mount tantalum capacitors can have low enough
impedance to keep the LTC1504 happy in some circuits.
Often the RMS current capacity of the input bypass capaci-
tors is more important to capacitor selection than value.
Buck converters like the LTC1504 are hard on input
capacitors, since the current flow alternates between the
full load current and near zero during every clock cycle. In
the worst case (50% duty cycle or V
OUT
= 0.5V
IN
) the RMS
current flow in the input capacitor is half of the total load
current plus half the ripple current in the inductor—
perhaps 300mA in a typical 500mA load current applica-
tion. This current flows through the ESR of the input
bypass capacitor, heating it up and shortening its life,
sometimes dramatically. Many ordinary electrolytic ca-
pacitors that look OK at fist glance are not rated to
withstand such currents—check the RMS current rating
before you specify a device! If the RMS current rating isn’t
specified, it should not be used as an input bypass
capacitor. Again, low ESR electrolytic and surge tested
tantalums usually do well in LTC1504 applications and
have high RMS current ratings. The local ceramic bypass
capacitor usually has negligible ESR allowing it to with-
stand large RMS currents without trouble. Table 1 shows
typical surface mount capacitors that make acceptable
input bypass capacitors in LTC1504 applications.
Table 1. Representative Surface Mount Input Bypass Capacitors
PART
VALUE
ESR
AVX
TPSC226M016R0375
22
μ
F
0.38
TPSD476M016R0150
47
μ
F
0.15
TPSE107M016R0125
100
μ
F
0.13
1206YC105M
1
μ
F
Low
1210YG106Z
10
μ
F
Low
Sanyo
16SN33M
33
μ
F
0.15
16SN68M
68
μ
F
0.1
16CV100GX
100
μ
F
0.44
16CV220GX
220
μ
F
0.34
Sprague
593D476X0016D2W
47
μ
F
0.17
593D107X0016E2W
100
μ
0.15
MAX RMS
TYPE
HEIGHT
0.54A
0.86A
1.15A
>1A
>1A
Tantalum
Tantalum
Tantalum
X7R Ceramic 1.5mm
Y5V Ceramic 1.7mm
2.6mm
2.9mm
4.1mm
1.24A
1.65A
0.23A*
0.28A*
OS-CON
OS-CON
Electrolytic
Electrolytic
7mm
7mm
6mm
7.7mm
0.93A
1.05A
Tantalum
Tantalum
2.8mm
4mm
*Note: Use multiple devices in parallel or limit output current to prevent capacitor overload.
Inductor
The LTC1504 requires an external inductor to be con-
nected from the switching node SW to the output node
where the load is connected. Inductor requirements are
fairly straightforward; it must be rated to handle continu-
ous DC current equal to the maximum load current plus
APPLICATIO
S I
FOR
ATIO
U
W
U
U
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