参数资料
| 型号： | LT1946EMS8E#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 6/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST 1.5A 8MSOP |
| 标准包装： | 2,500 |
| 类型： | 升压（升压） |
| 输出数： | 1 |
| 输入电压： | 2.45 V ~ 16 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 2.7MHz |
| 电流 - 输出： | 1.5A |
| 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： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-MSOP-EP |
LT1946
APPLICATIO S I FOR ATIO
Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multilayer ceramic capacitors are an excellent choice, as
they have an extremely low ESR and are available in very
small packages. X5R or X7R dielectrics are preferred, as
these materials retain the capacitance over wide voltage
and temperature ranges. A 4.7 μ F to 20 μ F output capacitor
is sufficient for most applications, but systems with very
low output currents may need only a 1 μ F or 2.2 μ F output
capacitor. Solid tantalum or OS-CON capacitors can be
used, but they will occupy more board area than a ceramic
and will have a higher ESR. Always use a capacitor with a
sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1946. A 2.2 μ F to 4.7 μ F input capacitor is
sufficient for most applications. Table 2 shows a list of
several ceramic capacitor manufacturers. Consult the
manufacturers for detailed information on their entire
V OUT
20mV/DIV
AC COUPLED
I LI
0.5A/DIV
AC COUPLED
R C = 7.5k 200 μ s/DIV 1946 F03a
Figure 3a. Transient Response Shows Excessive Ringing
V OUT
20mV/DIV
AC COUPLED
I LI
0.5A/DIV
AC COUPLED
selection of ceramic parts.
R C = 18k
200 μ s/DIV
1946 F03b
Table 2. Ceramic Capacitor Manufacturers
Figure 3b. Transient Response is Better
Taiyo Yuden
AVX
(408) 573-4150
www.t-yuden.com
(803) 448-9411
www.avxcorp.com
Murata
Compensation—Adjustment
(714) 852-2001
www.murata.com
V OUT
20mV/DIV
AC COUPLED
To compensate the feedback loop of the LT1946, a series
resistor-capacitor network should be connected from the
COMP pin to GND. For most applications, a capacitor in
the range of 220pF to 680pF will suffice. A good starting
value for the compensation capacitor, C C , is 470pF. The
compensation resistor, R C , is usually in the range of 20k
to 100k. A good technique to compensate a new applica-
tion is to use a 100k ? potentiometer in place of R C , and
use a 470pF capacitor for C C . By adjusting the potentiom-
eter while observing the transient response, the optimum
value for R C can be found. Figures 3a to 3c illustrate this
process for the circuit of Figure 1 with a load current
stepped from 250mA to 300mA. Figure 3a shows the tran-
I LI
0.5A/DIV
AC COUPLED
R C = 49.9k 200 μ s/DIV 1946 F03b
Figure 3c. Transient Response is Well Damped
poor as evidenced by the excessive ringing in the output
voltage and inductor current. In Figure 3b, the value of R C
is increased to 18k, which results in a more damped re-
sponse. Figure 3c shows the results when R C is increased
further to 49.9k. The transient response is nicely damped
and the compensation procedure is complete. The COMP
pin provides access to an internal resistor (120k) and
capacitor (90pF). For some applications, these values will
sient response with R C equal to 7.5k. The phase margin is
6
suffice and no external R C and C C will be needed.
1946fb
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