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| 型号： | MAX1771CSA+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM 8-SOIC |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 92% |
| 电源电压： | 3 V ~ 16.5 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
MAX1771
12V or Adjustable, High-Efficiency,
Low I Q , Step-Up DC-DC Controller
The control circuitry allows the IC to operate in continu-
ous-conduction mode (CCM) while maintaining high
efficiency with heavy loads. When the power switch is
turned on, it stays on until either 1) the maximum on-
FB
R2
V OUT
time one-shot turns it off (typically 16μs later), or 2) the
switch current reaches the peak current limit set by the
MAX1771
R1
C5*
current-sense resistor.
The MAX1771 switching frequency is variable (depend-
( V OUT -1 )
ing on load current and input voltage), causing variable
switching noise. However, the subharmonic noise gen-
erated does not exceed the peak current limit times the
filter capacitor equivalent series resistance (ESR). For
example, when generating a 12V output at 500mA from
GND
R1 = 10k ? TO 500k ?
V
R2 = R1
REF
V REF = 1.5V
a 5V input, only 100mV of output ripple occurs using
the circuit of Figure 2a.
Low-Voltage Start-Up Oscillator
The MAX1771 features a low input voltage start-up oscil-
lator that guarantees start-up with no load down to 2V
when operating in bootstrapped mode and using inter-
nal feedback resistors. At these low voltages, the supply
voltage is not large enough for proper error-comparator
* SEE TEXT FOR VALUE
Figure 3. Adjustable Output Circuit
R1 and R2 configured as shown in Figure 3. For
adjustable-output operation, select feedback resistor
R1 in the 10k ? to 500k ? range. R2 is given by:
(
operation and internal biasing. The start-up oscillator
has a fixed 50% duty cycle and the MAX1771 disre-
gards the error-comparator output when the supply volt-
V –– –
R2 = (R1) –– OUT -1
V REF
)
age is less than 2.5V. Above 2.5V, the error-comparator
and normal one-shot timing circuitry are used. The low-
voltage start-up circuitry is disabled if non-bootstrapped
mode is selected (FB is not tied to ground).
Shutdown Mode
When SHDN is high, the MAX1771 enters shutdown
mode. In this mode, the internal biasing circuitry is
turned off (including the reference) and V OUT falls to a
diode drop below V IN (due to the DC path from the
input to the output). In shutdown mode, the supply
current drops to less than 5μA. SHDN is a TTL/CMOS
logic-level input. Connect SHDN to GND for normal
operation.
Design Procedure
Setting the Output Voltage
To set the output voltage, first determine the mode of
operation, either bootstrapped or non-bootstrapped.
Bootstrapped mode provides more output current capa-
bility, while non-bootstrapped mode reduces the supply
current (see the Typical Operating Characteristics ). If a
decaying voltage source (such as a battery) is used,
see the additional notes in the Low Input Voltage
Operation section.
The MAX1771’s output voltage can be adjusted from
very high voltages down to 3V, using external resistors
Maxim Integrated
where V REF equals 1.5V.
For preset-output operation, tie FB to GND (this
forces bootstrapped-mode operation.
Figure 2 shows various circuit configurations for boot-
strapped/non-bootstrapped, preset/adjustable operation.
Determining R SENSE
Use the theoretical output current curves shown in
Figures 4a–4d to select R SENSE . They were derived
using the minimum (worst-case) current-limit compara-
tor threshold value over the extended temperature
range (-40°C to +85°C). No tolerance was included for
R SENSE . The voltage drop across the diode was
assumed to be 0.5V, and the drop across the power
switch r DS(ON) and coil resistance was assumed to be
0.3V.
Determining the Inductor (L)
Practical inductor values range from 10μH to 300μH.
22μH is a good choice for most applications. In appli-
cations with large input/output differentials, the IC ’s
output current capability will be much less when the
inductance value is too low, because the IC will always
operate in discontinuous mode. If the inductor value
is too low, the current will ramp up to a high level before
the current-limit comparator can turn off the switch.
The minimum on-time for the switch (t ON (min)) is
9
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相关代理商/技术参数 |
参数描述 |
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| MAX1771CSA-TG05 | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1771CSA-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1771EPA | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1771EPA+ | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1771ESA | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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