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参数资料
| 型号： | MAX1817EUB+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST 125MA DL 10UMAX |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 升压（升压） |
| 输出类型： | 两者兼有 |
| 输出数： | 2 |
| 输出电压： | 3.3V 或可调主电源，-28 V ~ 28 V 或可调副电源 |
| 输入电压： | 1.5 V ~ 5.5 V |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 125mA |
| 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-µMAX |
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
V IN
C1
10 μ F
L2
10 μ H
L1
10 μ H
D1
V IN
C1
10 μ F
L2
10 μ H
L1
10 μ H
D1
OFF
OFF
ON
LCD
ON
MAIN
LX LXLCD
ONLCD FBLCD
ON MAX1817 OUT
D2
4.7pF
C4
R3
300k
C3
22 μ F
LCD 18V
C2
R1 1 μ F
1M
R2 75k
MAIN 5V
OFF
OFF
ON
LCD
ON
MAIN
LX LXLCD
ONLCD FBLCD
ON MAX1817 OUT
FB
D2
4.7pF
C4
C3
22 μ F
LCD 18V
C2
R1 1 μ F
1M
R2 75k
MAIN 3.3V
AGND
FB
GND
R4
100k
AGND
GND
Figure 2. Setting Main Output Voltage Using External Resistors
Low-Voltage Startup
The MAX1817 ’ s internal circuitry is powered from OUT.
The main step-up converter has a low-voltage startup
circuit to control main DC-DC converter operation until
V OUT exceeds the 2.2V (typ) undervoltage lockout
threshold. The minimum startup voltage is a function of
load current (see Typical Operating Characteristics ).
The MAX1817 main converter typically starts up into a
35 ? load with input voltages down to +1.5V, allowing
startup with two alkaline cells even in deep discharge.
Shutdown: ON and ONLCD
The MAX1817 features independent shutdown control
of the main and LCD step-up converters. With both
converters shut down, supply current is reduced to
0.1μA. A logic low at ON shuts down the main step-up
converter, and LX enters a high-impedance state.
However, the main output remains connected to the
input through the inductor and output rectifier, holding
V OUT to one diode drop below the input voltage when
the main converter is shut down. If the input voltage is
sufficiently high to drive V OUT above the undervoltage
lockout voltage, the LCD step-up converter operates.
A logic low at ONLCD shuts down the LCD step-up
converter, and LXLCD enters a high-impedance state.
The LCD output remains connected to the input
through the inductor and output rectifier, holding it to
one diode drop below the input.
Figure 3. Typical Application Circuit
___________________Design Procedure
Setting the Main Output Voltage
The main step-up converter feedback input (FB) fea-
tures Dual Mode operation. With FB grounded, the
main output voltage is preset to 3.3V. It can also be
adjusted from 2.5V to 5.5V with external resistors R3
and R4 as shown in Figure 2. To set the output voltage
externally, select resistor R4 from 10k ? to 100k ? .
Calculate R3 using:
R3 = R4 [(V OUT / V FB ) – 1]
where V FB = 1.25V, and V OUT can range from 2.5V to
5.5V.
Setting the LCD Output Voltage
Set the LCD output voltage with two external resistors
R1 and R2 as shown in Figure 3. Since the input leak-
age current at FBLCD has a maximum of 50nA, large
resistors can be used without significant accuracy loss.
Begin by selecting R2 in the 10k ? to 100k ? range, and
calculate R1 using the following equation:
R1 = R2 [(V LCD / V FBLCD ) – 1]
where V FBLCD = 1.25V, and V LCD can range from V IN
to 28V.
_______________________________________________________________________________________
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