参数资料
型号: LT3470EDDB#TRMPBF
厂商: Linear Technology
文件页数: 11/20页
文件大小: 0K
描述: IC REG BUCK ADJ 0.2A 8DFN
标准包装: 500
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 1.25 V ~ 16 V
输入电压: 4 V ~ 40 V
PWM 型: Burst Mode?
电流 - 输出: 200mA
同步整流器:
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 8-DFN(3x2)
LT3470
APPLICATIONS INFORMATION
V IN
V IN
CeramicCapacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT3470. Not all ceramic capacitors are
suitable. X5R and X7R types are stable over temperature
and applied voltage and give dependable service. Other
types, including Y5V and Z5U have very large temperature
and voltage coefficients of capacitance. In an application
circuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
Ceramic capacitors are piezoelectric. The LT3470’s switch-
ing frequency depends on the load current, and at light
loads the LT3470 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3470
operates at a lower current limit during Burst Mode opera-
tion, the noise is typically very quiet to a casual ear. If this
audible noise is unacceptable, use a high performance
electrolytic capacitor at the output. The input capacitor
can be a parallel combination of a 2.2μF ceramic capacitor
and a low cost electrolytic capacitor.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT3470. A ceramic
input capacitor combined with trace or cable inductance
forms a high quality (under damped) tank circuit. If the
LT3470 circuit is plugged into a live supply, the input volt-
age can ring to twice its nominal value, possibly exceeding
the LT3470’s rating. This situation is easily avoided; see
the Hot-Plugging Safely section.
Table 3. Capacitor Vendors
BOOST and BIAS Pin Considerations
Capacitor C3 and the internal boost Schottky diode (see
Block Diagram) are used to generate a boost voltage that
is higher than the input voltage. In most cases a 0.22μF
capacitor will work well. Figure 2 shows two ways to ar-
range the boost circuit. The BOOST pin must be more than
2.5V above the SW pin for best efficiency. For outputs of
3.3V and above, the standard circuit (Figure 2a) is best.
For outputs between 2.5V and 3V, use a 0.47μF. For lower
output voltages the boost diode can be tied to the input
C3
0.22μF
V IN BOOST
LT3470
SW V OUT
BIAS
GND
V BOOST – VSW ? V OUT
MAX V BOOST ? V IN + V OUT
(2a)
C3
0.22μF
V IN BOOST
LT3470
BIAS SW V OUT
GND
3470 F02
V BOOST – VSW ? V IN
MAX V BOOST ? 2V IN
(2b)
Figure 2. Two Circuits for Generating the Boost Voltage
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
PHONE
(714) 373-7366
(864) 963-6300
(408) 749-9714
(404) 436-1300
(864) 963-6300
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
COMMENTS
EEF Series
T494, T495
POSCAP
TPS Series
3470fd
11
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