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参数资料
| 型号： | MAX687CSA-T |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 固定正电压单路输出LDO稳压器 |
| 英文描述： | High-Accuracy, Low-Dropout Linear Regulators |
| 中文描述： | 3.3 V FIXED POSITIVE LDO REGULATOR, PDSO8 |
| 封装： | 0.150 INCH, SO-8 |
| 文件页数： | 10/12页 |
| 文件大小： | 103K |
| 代理商： | MAX687CSA-T |
shuts down. Once the MAX687 is shut down, it can
only be turned on again when (a) the ON pin is pulsed
high, and (b) the conditions that triggered shutdown
have changed (e.g., the load has been reduced or the
input voltage has increased). In order for the MAX687
to latch into its on state, the ON pulse must remain high
until the output voltage has risen above the shutdown
threshold. The internal shutdown can be used to pre-
vent deep discharge of a battery, for example, to pro-
vide “self backup” of CMOS RAM or to protect the
battery itself.
The RC circuit attached to the ON input in Figure 1
achieves automatic start-up at power-on by delivering a
brief pulse whenever the input voltage is suddenly
applied. This circuit is not suitable for applications
where the input voltage rises slowly. The RC values
should be chosen to keep ON high until the output rises
above about 3.13V. The values shown in Figure 1 for
C4 and R1 (0.1F and 10k
) are suitable for most
applications. To ensure start-up when the input voltage
is very close to the circuit’s dropout voltage, when the
circuit is used to drive a very large capacitive load, or
for high-power circuits (ILOAD > 3A), increase the value
of R1 to increase the ON pulse width.
The 3.3V MAX688 and the 3.0V MAX689 incorporate
the same PFO warning whenever VOUT droops.
However, the MAX688/MAX689 do not automatically
shut down when the output voltage drops even further.
Instead, the SHDN input controls external shutdown.
As SHDN is pulled low, the chip first enters a low-cur-
rent standby state (<25A). The threshold at which
standby mode is entered is precisely controlled (±2%)
so the output can be turned off at a well-defined point.
70mV of hysteresis between the standby and on states
prevents chatter between the two modes. The voltage
applied to the SHDN pin can be derived from a resis-
tive divider from VIN. When VSHDN is less than 1.2V,
the output is off. The device is fully shut down (<1A)
when SHDN is pulled below 200mV. SHDN is not
latched, and as SHDN is raised, the MAX688/MAX689
exit shutdown and enter the standby mode. At the
higher SHDN threshold, the output is turned on.
Figure 1 shows a typical circuit for the MAX687, and
Figure 2 shows the same circuit configured for the
MAX688/MAX689.
The accuracy of the output current limit depends on
accurate knowledge of the PNP pass transistor’s cur-
rent gain (hFE). With RB = 12
, BLIM limits base cur-
rent to 6mA (IBASE = 0.1V / (RB + 5
)). See Base-
Current Limiting section.
The PFO comparators on all three devices, and the internal
shutdown comparator on the MAX687, reject high-speed
spikes (<100s). This reduces the PFO output’s noise sen-
sitivity, and stops the MAX687 from being shut down inad-
vertently when there is noise on the input supply.
_______________Transistor Selection
Specifications
The PNP pass transistor must meet specifications for
current gain,
power dissipation, and
collector current.
The hFE influences the maximum output current the cir-
cuit can deliver. The largest guaranteed output current
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
_______________________________________________________________________________________
7
MAX687
OUT
3.3V @ 500mA
POWER FAIL
PFO
CC
C1
2.2
F
C4
0.1
F
BLIM
GND
BASE
Q1 FZT749
RB 12
C3
10nF
IN
ON
+5V INPUT
GND
R1
10k
ON CAN BE DRIVEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED.
C2
68
F
Figure 1. MAX687 Operating Circuit
MAX688
MAX689
OUT
3.3V/ 3.0V @ 500mA
POWER FAIL
PFO
CC
C1
2.2
F
BLIM
GND
BASE
Q1 FZT749
RB 12
C3
10nF
IN
SHDN
+5V INPUT
GND
R2
100k
C2
68
F
ON / OFF
Figure 2. MAX688/MAX689 Operating Circuit
相关PDF资料 |
PDF描述 |
|---|---|
| MAX687CUA-T | High-Accuracy, Low-Dropout Linear Regulators |
| MAX687ESA-T | High-Accuracy, Low-Dropout Linear Regulators |
| MAX688CSA-T | High-Accuracy, Low-Dropout Linear Regulators |
| MAX688CUA-T | High-Accuracy, Low-Dropout Linear Regulators |
| MAX688ESA-T | High-Accuracy, Low-Dropout Linear Regulators |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX687CUA | 功能描述:低压差稳压器 - LDO High-Accuracy LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX687CUA-T | 功能描述:低压差稳压器 - LDO High-Accuracy LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX687EPA | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX687ESA | 功能描述:低压差稳压器 - LDO High-Accuracy LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX687ESA-T | 功能描述:低压差稳压器 - LDO High-Accuracy LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
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