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参数资料
| 型号： | MAX1855 |
| 厂商： | Maxim Integrated Products, Inc. |
| 元件分类： | 数字信号处理 |
| 英文描述： | Fixed-Point Digital Signal Processor 352-FC/CSP 0 to 0 |
| 中文描述： | 高速、数字可调、同步降压型控制器，集成电压定位电路 |
| 文件页数： | 18/33页 |
| 文件大小： | 840K |
| 代理商： | MAX1855 |
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M
High-Speed, Adjustable, Synchronous Step-Down
Controllers with Integrated Voltage Positioning
18
______________________________________________________________________________________
low-side switch on-time. The resulting low-side gate-
drive waveform is forced to be the complement of the
high-side gate-drive waveform. This, in turn causes the
inductor current to reverse at light loads, as the PWM
loop strives to maintain a duty ratio of V
OUT
/V+. The
benefit of forced-PWM mode is to keep the switching
frequency nearly constant, but it results in higher no-
load supply current that can be 10mA to 40mA,
depending on the external MOSFETs and switching fre-
quency.
Forced-PWM mode is most useful for minimizing audio-
frequency noise and improving the cross-regulation of
multiple-output applications that use a flyback trans-
former or coupled inductor.
Current-Limit Circuit (ILIM)
The current-limit circuit employs a unique
“
valley
”
cur-
rent-sensing algorithm. If the current-sense signal is
above the current-limit threshold, the MAX1716/
MAX1854/MAX1855 will not initiate a new cycle (Figure
4). The actual peak current is greater than the current-
limit threshold by an amount equal to the inductor rip-
ple current. Therefore, the exact current-limit
characteristic and maximum load capability are a func-
tion of the current-limit threshold, inductor value, and
input voltage. The reward for this uncertainty is robust,
loss-less overcurrent sensing. When combined with the
UVP protection circuit, this current-limit method is effec-
tive in almost every circumstance.
There is also a negative current limit that prevents
excessive reverse inductor currents when V
OUT
is sink-
ing current. The negative current-limit threshold is set to
approximately 120% of the positive current limit and
therefore tracks the positive current limit when ILIM is
adjusted.
The MAX1716/MAX1854/MAX1855 measure the current
by sensing the voltage between CS and PGND.
Connect an external sense resistor between the source
of the low-side N-channel MOSFET and PGND. This
same resistor is also used to generate the input voltage
for the VPS input (see
Setting Voltage Positioning
).
Reducing the sense voltage increases the relative mea-
surement error. However, the configuration eliminates
the uncertainty of using the low-side MOSFET on-resis-
tance to measure the current, so the resulting current-
limit tolerance is tighter when sensing with a 1% sense
resistor.
In some applications, the signal required for voltage
positioning is much smaller than the minimum current-
limit voltage (50mV). There are two options for address-
ing this issue. One method is to use a larger
current-sense resistor to develop the appropriate cur-
rent-limit voltage and divide down this signal to obtain
the desired VPS input. This solution provides the maxi-
mum current-limit accuracy. Alternatively, select a
sense resistance to generate the desired VPS voltage
and connect CS to LX. This results in minimum power-
dissipation with reduced current-limit accuracy. The
default 120mV current limit (ILIM = V
CC
) accommo-
dates current-limit detection using the low-side power
MOSFET and low-value sense resistor.
The voltage at ILIM sets the current-limit threshold. For
voltages from 500mV to 2V, the current-limit threshold
voltage is precisely 0.1
×
V
ILIM
. Set this voltage with a
resistive divider between REF and GND. The current-
limit threshold defaults to 120mV when ILIM is tied to
SHDN
0
SKIP
X
DL
High
MODE
Shutdown
COMMENTS
Micropower shutdown state.
1
GND
Switching
Normal
Operation
Automatic switchover from PWM mode to pulse-skipping
PFM mode at light loads. Prevents inductor current from
recirculating into the input.
1
V
CC
Switching
Forced PWM
Low-noise forced-PWM mode causes inductor current to
reverse at light loads and suppresses pulse-skipping
operation.
1
Below GND
Switching
No-Fault Test
Mode
Test mode with overvoltage, undervoltage, and thermal
shutdown faults disabled. Otherwise, the converter
operates as if
SKIP
= GND.
X = Don
’
t care
Table 4. Operating Mode Truth Table
相关PDF资料 |
PDF描述 |
|---|---|
| MAX1854EEG | High-Speed, Adjustable, Synchronous Step-Down Controllers with Integrated Voltage Positioning |
| MAX1855EEG | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
| MAX1854 | High-Speed, Adjustable, Synchronous Step-Down Controllers with Integrated Voltage Positioning |
| MAX1857EUA47 | 500mA, Low-Dropout, Ripple-Rejecting LDO in MAX |
| MAX1857 | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1855EEG | 功能描述:DC/DC 开关控制器 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 |
| MAX1855EEG+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1855EEG-T | 功能描述:DC/DC 开关控制器 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 |
| MAX1855EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1716 MAX1854 MAX1855 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 |
| MAX1856EUB | 功能描述:电信线路管理 IC RoHS:否 制造商:STMicroelectronics 产品:PHY 接口类型:UART 电源电压-最大:18 V 电源电压-最小:8 V 电源电流:30 mA 最大工作温度:+ 85 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:VFQFPN-48 封装:Tray |
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