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参数资料
| 型号： | MAX857ESA+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 0.15A 8SOIC |
| 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： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 2.7 V ~ 6 V |
| 输入电压： | 0.8 V ~ 6 V |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 150mA |
| 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-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
3.3V/5V or Adjustable-Output,
Step-Up DC-DC Converters
V OUT = V REF ( _________ )
V OUT
Logic Inputs and Outputs
The 3/5 input is internally diode clamped to GND and
OUT, and should not be connected to signals outside
this range. The SHDN input and LBO output (open-
drain) are not clamped to V+ and can be pulled as high
as 7V regardless of the voltage at OUT . Do not leave
control inputs (3/5, LBI, or SHDN) floating.
__________________Design Procedure
Output Voltage Selection
For the MAX856/MAX858,you can select a 3.3V or – 5V
output voltage under logic control, or by tying 3/ 5 to
GND or OUT. Efficiency is typically better than 80%
over a 2mA to 100mA (MAX856/MAX857) load range.
The device is internally bootstrapped, with power
derived from the output voltage (via OUT). When the
output is in 5V mode, the higher internal supply voltage
results in lower switch-transistor on-resistance, slightly
greater output power, and higher efficiency.
Bootstrapping allows the battery voltage to sag to 0.8V
once the system is started. Therefore, the battery volt-
age ranges from (V OUT + V D ) to 0.8V (where V D is the
forward drop of the Schottky rectifier). If the battery volt-
age exceeds the programmed output voltage, the out-
V IN
put will follow the battery voltage. This is acceptable in
many systems; however, the input or output voltage
must not be forced above 7V.
The MAX857/MAX859’s output voltage is set by two
resistors, R1 and R2 (Figure 2b), which form a voltage
divider between the output and FB. Use the following
equation to determine the output voltage:
R1 + R2
R2
where V REF = 1.25V.
To simplify resistor selection:
R1 = R2 ( _______ - 1)
V REF
Since the input bias current at FB has a maximum value
of 100nA, large values (10k ? to 300k ? ) can be used
for R1 and R2 with no significant accuracy loss. For 1%
error, the current through R1 should be at least 100
times FB’s bias current.
V IN
R3
C1*
47 μ H
L1
D1
R3
C1*
47 μ H
L1
D1
5
LBI
LX
8
1N5817
V OUT
5
LBI
LX
8
1N5817
V OUT
R4
1
MAX856/MAX858
OUT
3/5
SHDN
6
2
R1
OUTPUT
C2*
R4
1
MAX857/MAX859
OUT
FB
SHDN
6
2
R1
C2*
SELECT
C3
0.1 μ F
3
REF
GND
LBO
4
C3
0.1 μ F
3
REF
GND
LBO
4
R2
7
*C1 = C2 = 68 μ F FOR MAX856
C1 = C2 = 22 μ F FOR MAX858
Figure 2a. Standard Application Circuit—Preset Output
Voltage
7
*C1 = C2 = 68 μ F FOR MAX857
C1 = C2 = 22 μ F FOR MAX859
Figure 2b. Standard Application Circuit—Adjustable Output
Voltage
8
_______________________________________________________________________________________
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