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| 型号： | MAX8654EVKIT+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 11/17页 |
| 文件大小： | 0K |
| 描述： | EVAL KIT MAX8654, MAX8688 |
| 标准包装： | 1 |
| 系列： | * |
12V, 8A 1.2MHz
Step-Down Regulator
Controller Function
The controller logic block is the central processor that
determines the duty cycle of the high-side MOSFET
under different line, load, and temperature conditions.
Under normal operation, where the current-limit and
temperature protection are not triggered, the controller
logic block takes the output from the PWM comparator
and generates the driver signals for both high-side and
Soft-Start and REFIN
The MAX8654 utilizes an adjustable soft-start function
to limit inrush current during startup. An 8μA (typ) cur-
rent source charges an external capacitor connected to
SS to increase the capacitor voltage in a controlled
manner. The soft-start time is adjusted by the value of
the external capacitor from SS to GND. The required
capacitance value is determined as:
low-side MOSFETs. The break-before-make logic and
the timing for charging the bootstrap capacitors are
calculated by the controller logic block. The error signal
from the voltage-error amplifier is compared with the
C =
8 μ A × t SS
0 . 6 V
ramp signal generated by the oscillator at the PWM
comparator, and thus the required PWM signal is pro-
duced. The high-side switch is turned on at the begin-
ning of the oscillator cycle and turns off when the ramp
voltage exceeds the V COMP signal or when the current-
limit threshold is exceeded. The low-side switch is then
turned on for the remainder of the oscillator cycle.
Current Limit
The MAX8654 adjustable current limit is set by a resis-
where t SS is the required soft-start time in seconds.
The MAX8654 also features an external reference input
(REFIN). The IC regulates FB to the voltage applied to
REFIN. The internal soft-start is not available when
using an external reference. A method of soft-start
when using an external reference is shown in Figure 2.
When using an external reference, in order to avoid cur-
rent limit during soft-start, care should be taken to
ensure the following condition:
+ I OUT < I LXLIM ? P ? P
tor, R ILIM , connected from ILIM to GND. The current
through R ILIM determines the LX current-limit trip point:
R ILIM (k ? ) = 800 / I LXLIM (A)
C OUT ×
dV REFIN
dt
I
2
where I LXLIM is the LX current-limit threshold. The valid
R ILIM range is 40k ? to 200k ? . R ILIM of 100k ? sets a typ-
ical peak current limit of 8A, sourcing or sinking at LX.
When current flowing out of LX exceeds this limit,
the high-side MOSFET turns off and the synchronous
rectifier turns on. The synchronous rectifier remains on
until the inductor current falls below the low-side cur-
rent limit. This lowers the duty cycle and causes the
output voltage to drop until the current limit is no longer
exceeded.
where I OUT is the maximum output current, C OUT is the
output capacitance, and I P-P is the peak-to-peak induc-
tor ripple current.
Connect REFIN to SS to use the internal 0.6V reference.
R1
REFIN
When the negative current limit is exceeded, the device
turns off the synchronous rectifier, forcing the inductor
R2
C
MAX8654
current to flow through the high-side MOSFET body
diode, back to the input, until the beginning of the next
cycle, or until the inductor current drops to zero.
The MAX8654 uses a hiccup mode to prevent overheat-
ing during short-circuit output conditions. The device
enters hiccup mode when V FB drops below 420mV for
more than 12μs, pulling COMP and REFIN low. The IC
turns off for 900 clock cycles and then enters soft-start
for 110 clock cycles. If the short-circuit condition
remains, the IC shuts down for another 512 clock
cycles. The IC repeats this behavior until the short-cir-
cuit condition is removed.
Figure 2. Typical Soft-Start Implementation with External
Reference
______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8654EVKIT+ | 功能描述:电源管理IC开发工具 MAX8654 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX8655ETN/GG8 | 功能描述:直流/直流开关调节器 RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MAX8655ETN+ | 功能描述:直流/直流开关调节器 25A Int MOSFET Step-Down Regulator RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MAX8655ETN+T | 功能描述:直流/直流开关调节器 25A Int MOSFET Step-Down Regulator RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| MAX8655ETN+TW | 功能描述:直流/直流开关调节器 25A Int MOSFET Step-Down Regulator RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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