参数资料
型号: MAX1921EVKIT
厂商: Maxim Integrated Products
文件页数: 7/11页
文件大小: 0K
描述: EVAL KIT FOR MAX1921
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 1
主要目的: DC/DC,步降
输出及类型: 1,非隔离
输出电压: 1.8V
电流 - 输出: 400mA
输入电压: 2 ~ 5.5 V
稳压器拓扑结构: 降压
板类型: 完全填充
已供物品:
已用 IC / 零件: MAX1921
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
V OUT ( V IN ? V OUT )
dielectric. The input capacitor filters peak currents and
noise at the voltage source and, therefore, must meet
the input ripple requirements and voltage rating.
Calculate the maximum RMS input current as:
I IN ( RMS ) = I OUT ( MAX ) ×
V IN
The output capacitor, C OUT , may be either ceramic or
tantalum depending upon the chosen application cir-
cuit (see Figures 1 through 4). Table 3 lists some sug-
gested capacitor suppliers.
Ceramic Output Capacitor
For ceramic C OUT , use the application circuit of Figure 1
or Figure 2. Calculate the minimum capacitor value as:
Tantalum Output Capacitor
For tantalum C OUT , use the application circuit of Figure
3 or Figure 4. With tantalum C OUT , the equivalent series
resistance (ESR) of C OUT must be large enough for sta-
bility. Generally, 25mV of ESR-ripple at the feedback
node is sufficient. The simplified calculation is:
ESR COUT ( MIN ) = 8 . 0 × 10 ? 2 × V OUT
Because tantalum capacitors rarely specify minimum
ESR, choose a capacitor with typical ESR that is about
twice as much as ESR COUT (MIN). Although ESRs
greater than this work, output ripple becomes larger.
For tantalum C OUT , calculate the minimum output
capacitance as:
C OUT ( MIN ) = 2 . 5 × 10 ? 6 × V CRITICAL
Select the next standard value larger than C OUT (MIN).
C OUT ( MIN ) = 1 . 25 ×
L × I OUT ( MAX )
ESR COUT ( MIN ) × V CRITICAL
The C OUT (MIN) calculation already includes a margin
for capacitor tolerance. Values much larger than
C OUT (MIN) always improve transient performance and
stability, but capacitor size and cost increase.
The 1.25 multiplier is for capacitor tolerance. Select any
standard value larger than C OUT (MIN).
Feedback and Compensation
The MAX1921 has factory preset output voltages of
1.5V, 1.8V, 2.5V, 3V, and 3.3V, while the MAX1920 is
externally adjusted by connecting FB to a resistive volt-
age-divider. When using a ceramic output capacitor,
the feedback network must include a compensation
feed-forward capacitor, C FF .
INPUT
2V TO 5.5V
1
IN
LX
6
L
OUTPUT
UP TO 400mA
INPUT
2V TO 5.5V
1
IN
LX
6
L
OUTPUT
UP TO 400mA
C IN
R1
C OUT
C IN
C OUT
2
MAX1920
AGND PGND
5
C FF
2
MAX1921
AGND PGND
5
ON
3
SHDN
FB
4
ON
3
SHDN
OUT
4
OFF
R2
OFF
Figure 2. Typical Application Circuit (MAX1920)
Figure 3. MAX1921 Application Circuit Using Tantalum Output
Capacitor
_______________________________________________________________________________________
7
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