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参数资料
| 型号： | LT1941EFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG TRPL 28TSSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压），升压（升压），反相，Sepic |
| 输出类型： | 可调式 |
| 输出数： | 3 |
| 输出电压： | 1.25 V ~ 40 V |
| 输入电压： | 3.5 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.1MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
LT1941
APPLICATIONS INFORMATION
You can estimate output ripple with the following
Table 2. Low ESR Surface Mount Capacitors
equations:
V RIPPLE = ΔI L /(8 ? f ? C OUT ) for ceramic capacitors
and
V RIPPLE = ΔI L ? ESR for electrolytic capacitors (tantalum
and aluminum)
where ΔI L is the peak-to-peak ripple current in the inductor.
The RMS content of this ripple is very low so the RMS
current rating of the output capacitor is usually not of
VENDOR
Taiyo-Yuden
AVX
Kemet
Sanyo
Panasonic
TDK
TYPE
Ceramic
Ceramic
Tantalum
Tantalum
Tantalum Organic
Aluminum Organic
Tantalum or Aluminum Organic
Aluminum Organic
Ceramic
SERIES
TPS
T491,T494,T495
T520
A700
POSCAP
SP CAP
concern. It can be estimated with the formula:
I C(RMS) = ΔI L /√ 12
Another constraint on the output capacitor is that it must
have greater energy storage than the inductor; if the stored
energy in the inductor transfers to the output, the resulting
voltage step should be small compared to the regulation
voltage. For a 5% overshoot, this requirement indicates:
C OUT > 10 ? L ? (I LIM /V OUT ) 2
The low ESR and small size of ceramic capacitors make
them the preferred type for LT1941 applications. Not all
ceramic capacitors are the same, however. Many of the
higher value capacitors use poor dielectrics with high
temperature and voltage coef?cients. In particular, Y5V
and Z5U types lose a large fraction of their capacitance
with applied voltage and at temperature extremes.
Because loop stability and transient response depend on
Diode Selection
The catch diode (D1 from Figure 2) 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
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.
Table 3. Schottky Diodes
the value of C OUT , this loss may be unacceptable. Use
X7R and X5R types.
Electrolytic capacitors are also an option. The ESRs of
most aluminum electrolytic capacitors are too large to
deliver low output ripple. Tantalum, as well as newer,
lower-ESR organic electrolytic capacitors intended for
power supply use are suitable. Chose a capacitor with a
low enough ESR for the required output ripple. Because
the volume of the capacitor determines its ESR, both the
size and the value will be larger than a ceramic capacitor
PART
NUMBER
On Semiconductor
MBRM120E
MBRM140
Diodes Inc.
B120
B130
B220
B230
International Recti?er
10BQ030
20BQ030
V R
(V)
20
40
20
30
20
30
30
30
I AVE
(A)
1
1
1
1
2
2
1
2
V F AT 1A
(mV)
530
550
500
500
420
V F AT 2A
(mV)
595
500
500
470
470
that would give similar ripple performance. One bene?t
is that the larger capacitance may give better transient
response for large changes in load current. Table 2 lists
several capacitor vendors.
1941fb
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