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| 型号： | LT1373IS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/12页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG ADJ 8SOIC |
| 标准包装： | 100 |
| 类型： | 降压（降压），升压（升压），反相，Cuk，回扫，正向转换器 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.25 V ~ 35 V |
| 输入电压： | 2.7 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 250kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-SOIC |
| 产品目录页面： | 1327 (CN2011-ZH PDF) |
LT1373
APPLICATIO S I FOR ATIO
Many engineers have heard that solid tantalum capacitors
are prone to failure if they undergo high surge currents.
This is historically true and type TPS capacitors are
specially tested for surge capability, but surge ruggedness
is not a critical issue with the output capacitor. Solid
tantalum capacitors fail during very high turn-on surges,
which do not occur at the output of regulators. High
discharge surges, such as when the regulator output is
dead shorted, do not harm the capacitors.
Single inductor boost regulators have large RMS ripple
current in the output capacitor, which must be rated to
handle the current. The formula to calculate this is:
Output Capacitor Ripple Current (RMS)
DC
I RIPPLE (RMS) = I OUT 1 – DC
aluminum electrolytic capacitors may also be used and
have a high tolerance to turn-on surges.
Ceramic Capacitors
Higher value, lower cost ceramic capacitors are now
becoming available in smaller case sizes. These are tempt-
ing for switching regulator use because of their very low
ESR. Unfortunately, the ESR is so low that it can cause
loop stability problems. Solid tantalum capacitor ESR
generates a loop “zero” at 5kHz to 50kHz that is instrumen-
tal in giving acceptable loop phase margin. Ceramic ca-
pacitors remain capacitive to beyond 300kHz and usually
resonate with their ESL before ESR becomes effective.
They are appropriate for input bypassing because of their
high ripple current ratings and tolerance of turn-on surges.
Linear Technology plans to issue a Design Note on the use
of ceramic capacitors in the near future.
= I OUT
V OUT – V IN
V IN
Output Diode
Input Capacitors
The input capacitor of a boost converter is less critical due
to the fact that the input current waveform is triangular,
and does not contain large squarewave currents as is
found in the output capacitor. Capacitors in the range of
10 μ F to 100 μ F with an ESR (effective series resistance) of
0.3 ? or less work well up to a full 1.5A switch current.
Higher ESR capacitors may be acceptable at low switch
currents. Input capacitor ripple current for boost con-
verter is:
The suggested output diode (D1) is a 1N5818 Schottky or
its Motorola equivalent, MBR130. It is rated at 1A average
forward current and 30V reverse voltage. Typical forward
voltage is 0.42V at 1A. The diode conducts current only
during switch-off time. Peak reverse voltage for boost
converters is equal to regulator output voltage. Average
forward current in normal operation is equal to output
current.
Frequency Compensation
Loop frequency compensation is performed on the output
I RIPPLE =
0.3(V IN )(V OUT – V IN )
(f)(L)(V OUT )
of the error amplifier (V C pin) with a series R C network. The
main pole is formed by the series capacitor and the output
impedance ( ≈ 1M ? ) of the error amplifier. The pole falls in
f = 250kHz switching frequency
The input capacitor can see a very high surge current when
a battery or high capacitance source is connected “live”,
and solid tantalum capacitors can fail under this condition.
Several manufacturers have developed a line of solid
tantalum capacitors specially tested for surge capability
(AVX TPS series, for instance), but even these units may
fail if the input voltage approaches the maximum voltage
the range of 5Hz to 30Hz. The series resistor creates a
“zero” at 2kHz to 10kHz, which improves loop stability and
transient response. A second capacitor, typically one tenth
the size of the main compensation capacitor, is sometimes
used to reduce the switching frequency ripple on the V C
pin. V C pin ripple is caused by output voltage ripple
attenuated by the output divider and multiplied by the error
amplifier. Without the second capacitor, V C pin ripple is:
rating of the capacitor. AVX recommends derating capaci-
tor voltage by 2:1 for high surge applications. Ceramic and
V C Pin Ripple =
1.245(V RIPPLE )(g m )(R C )
V OUT
9
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