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参数资料
| 型号： | MAX686EEE+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST INV +/-27.5V 16QSOP |
| 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），反相 |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | ±27.5V |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 300kHz |
| 电流 - 输出： | 100mA |
| 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： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-QSOP |
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
Power-OK Comparator
POK is the input to the power-OK comparator. The
comparator drives an internal N-channel MOSFET. The
MOSFET’s open-drain output, LCDON , can drive an
external PNP transistor or P-channel MOSFET, switch-
ing a positive V OUT to the LCD (Figures 6 and 7). When
the voltage at POK exceeds 1.125V (power OK),
LCDON goes low, turning on the external PNP transis-
tor. When the voltage at POK drops below 1.125V
(power not OK), the external PNP transistor turns off,
cutting off power to the LCD display. This feature
ensures that the LCD display is not damaged due to
improper voltage levels. During shutdown or undervolt-
age lockout, LCDON is high impedance.
Shutdown Mode
When SHDN is low, the MAX686 enters shutdown
mode, in which the control circuit, POK comparator,
DAC output buffer, reference, and internal biasing cir-
cuitry turn off. The DAC setting is stored as long as V CC
remains above the DAC reset threshold. Supply current
drops to 1.5μA. SHDN is a logic-level input; connect it
to V CC for normal operation.
The output voltage in shutdown mode depends on the
output voltage polarity. In the positive output voltage
configuration (Figure 1), the output is directly connect-
ed to the input through the diode (D1) and the inductor
(L1). When the device is in shutdown mode, the output
voltage falls to one diode drop below the input voltage,
and any load connected to the output may still conduct
current. In the negative output voltage configuration
(Figures 2 and 3), there is no DC path between the
input and the output, and the output falls to GND in
shutdown mode.
Internal DAC
The MAX686 contains an internal 6-bit counter and
DAC to control the output voltage digitally (see the sec-
tion Setting the Output Voltage with the DAC). The UP
and DN input pins drive an internal up/down counter
that directly controls the DAC. To increase the magni-
tude of V OUT in the boost configuration, apply a rising
edge to UP. This decreases the DAC output voltage
one step and correspondingly increases V OUT.
Conversely, to decrease the magnitude of V OUT , apply
a rising edge to DN. This increases the DAC output
voltage one step and correspondingly decreases
V OUT . The UP and DN control direction reverses for a
negative output to maintain the same control direction of
the absolute magnitude of the output voltage. Upon
power-up, the DAC code internally goes to mid-scale.
The DAC’s internal counter does not roll over once it
reaches full scale or zero. Therefore, additional rising
edges to make the counter roll over are ignored, pre-
venting unexpected undervoltages or overvoltages.
Internal Reference
The MAX626’s 1.25V internal reference is accurate to
±2% over temperature. It can source up to 50μA of cur-
rent and should be bypassed with at least a 0.1μF
capacitor. See the Bypass Capacitors section.
Design Procedure
Setting the Output Voltage with the DAC
For either positive or negative output voltage applica-
tions, set the MAX686’s output voltage using three exter-
nal resistors (R1, R2, and R3) as shown in Figures 1, 2,
and 3. Since the input bias current at FB has a 50nA
maximum value, large resistors can be used in the
feedback loop without a significant loss of accuracy.
Select R1 to be in the 10k ? to 220k ? range and calcu-
late R2 and R3 using the applicable equations from the
following subsections.
Setting the Minimum Positive Output Voltage
The minimum output voltage is set with the resistor-
divider (R1-R2, Figure 1) from V OUT to FB. The mini-
mum output voltage occurs when V DACOUT = V FB =
1.25V. Therefore, R3 has no effect on the minimum out-
put voltage. Choose R1 to be 120k ? so that the current
in the divider is about 10μA. Then determine R2 as fol-
lows:
R2 = R1 x (V OUT(MIN) - V FB ) / V FB
For example, if V OUT(MIN) = 12.5V:
R2 = 120k ? x (12.5 - 1.25) / (1.25) =1.08M ?
Mount R1 and R2 close to the FB pin to minimize para-
sitic capacitance.
Setting the Maximum Positive Output Voltage
The DAC is adjustable from 0V to 1.25V in 64 steps,
and 1LSB = 1.25V / 63 = 19.8mV. Calculate R3 to
adjust V OUT with DACOUT (Figure 1).
For V OUT(MAX) = 25V and V OUT(MIN) = 12.5V, deter-
mine R3 as follows:
R3 = R2 x (V FB ) / (V OUT(MAX ) - V OUT(MIN) )
= 1.08M ? x (1.25) / (25 - 12.5) = 108k ?
The general form for V OUT as a function of the DAC out-
put (V DACOUT ) is:
V OUT = V OUT(MIN) + (V FB - V DACOUT ) x R2 / R3
At power-up, the DAC resets to mid-scale where
V DACOUT = 0.635V. Therefore, the output voltage after
power-up is:
V OUT(MID) = V OUT(MIN) + (1.25 - 0.635) x
R2 / R3 = 18.65V
10
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX686EVKIT | 功能描述:直流/直流开关转换器 Evaluation Kit for the MAX686 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX6870ETJ | 功能描述:监控电路 RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX6870ETJ+ | 功能描述:监控电路 EEPROM-Prog Hex Power-Sup Sequencer RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX6870ETJ+T | 功能描述:监控电路 EEPROM-Prog Hex Power-Sup Sequencer RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| MAX6870ETJ-T | 功能描述:监控电路 RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
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