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| 型号： | MAX1921EUT33+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 8/11页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 3.3V SOT23-6 |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 2 V ~ 5.5 V |
| 频率 - 开关： | 1.2MHz |
| 电流 - 输出： | 400mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-6 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | SOT-6 |
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
Table 3. Component Suppliers
MAX1920 Using Ceramic C OUT
When using the application circuit of Figure 2, the induc-
SUPPLIER
Coilcraft
Kemet
Murata
PHONE
847-639-6400
408-986-0424
814-237-1431
WEBSITE
www.coilcraft.com
www.kemet.com
www.murata.com
tor’s series resistance causes a small amount of load
regulation, as desired for a voltage-positioning load tran-
sient response. Choose R1 and R2 such that V OUT is
high at no load by about half of this load regulation:
R 1 = R 2 × ? OUT L OUT
? 1 ?
Sumida
Taiyo
USA
Japan
USA
847-956-0666
81-3-3607-5111
408-573-4150
www.sumida.com
www.T-Yuden.com
? V + R × I
? V REF
( MAX ) / 2
?
?
Yuden
Toko
Japan
USA
Japan
81-3-3833-5441
847-297-0070
81-3-3727-1161
www.yuden.co.jp
www.tokoam.com
www.toko.co.jp
where R2 is chosen in the 50k ? to 500k ? range, V REF
= 1.25V and R L is the typical series resistance of the
inductor. Use 1% or better resistors.
Next, calculate the equivalent resistance at the FB node as:
MAX1921 Using Ceramic COUT
When using the application circuit of Figure 1, the
inductor’s series resistance causes a small amount of
Re q = R 1 || R 2 =
R1 × R2
R 1 + R 2
C FF = 2 . 5 × 10
? 5
R 1 = R 2 × ? OUT ? 1 ?
load regulation, as desired for a voltage-positioning
load transient response. Choose R1 such that V OUT is
high at no load by about half of this load regulation. The
simplified calculation is:
R 1 = 5 × 10 4 × R L ( MAX )
where R L (MAX) is the maximum series resistance of the
inductor. Select a standard resistor value that is within
20% of this calculation.
Next, calculate C FF for 25mV ripple at the internal feed-
back node. The simplified calculation is:
R 1
where R1 is the standard resistor value that is used.
Select a standard capacitor value that is within 20% of
the calculated C FF .
Then, calculate C FF for 25mV ripple at FB. The simpli-
fied calculation is:
C FF = 2 . 5 × 10 ? 5 Re q
Select a standard capacitor value that is within 20% of
the calculated C FF .
MAX1920 Using Tantalum C OUT
When using the application circuit of Figure 4, choose
R1 and R2 such as to obtain the desired V OUT :
? V ?
? V REF ?
where R2 is chosen to be less than 50k ? and V REF =
1.25V. Use 1% or better resistors.
Layout Considerations
High switching frequencies make PC board layout a
very important part of design. Good design minimizes
INPUT
2V TO 5.5V
1
IN
LX
6
L
OUTPUT
UP TO 400mA
excessive EMI on the feedback paths and voltage gra-
dients in the ground plane, both of which can result in
C IN
2
MAX1920
AGND PGND
5
R1
C OUT
instability or regulation errors. Connect the inductor,
input filter capacitor, and output filter capacitor as
close to the device as possible, and keep their traces
short, direct, and wide. Connect their ground pins at a
single common node in a star ground configuration.
ON
OFF
3
SHDN
FB
4
The external voltage-feedback network should be very
close to the FB pin, within 0.2in (5mm). Keep noisy
R2
Figure 4. MAX1920 Application Circuit Using Tantalum Output
Capacitor
traces, such as the LX trace, away from the voltage-
feedback network; also keep them separate, using
grounded copper. The MAX1920/MAX1921 evaluation
kit data sheet includes a proper PC board layout and
routing scheme.
8
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