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| 型号： | MAX1957EUB+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-UMAX |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 360kHz |
| 占空比： | 96% |
| 电源电压： | 3 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
The chosen inductor’s saturation current rating must
exceed the expected peak inductor current (IPEAK).
Determine IPEAK as:
? LIR ?
? ?
I PEAK = I LOAD ( MAX ) + ? 2 ? × I LOAD ( MAX )
Setting the Current Limit
The MAX1953/MAX1954/MAX1957 use a lossless cur-
rent-sense method for current limiting. The voltage
drops across the MOSFETs created by their on-resis-
tances are used to sense the inductor current.
Calculate the current-limit threshold as follows:
FET. A good general rule is to allow 0.5% additional
resistance for each °C of MOSFET junction temperature
rise. The calculated V VALLEY must be less than V CS .
For the MAX1953, connect ILIM to GND for a short-
circuit current-limit voltage of 105mV, to V IN for 320mV
or leave ILIM floating for 210mV.
MOSFET Selection
The MAX1953/MAX1954/MAX1957 drive two external,
logic-level, N-channel MOSFETs as the circuit switch
elements. The key selection parameters are:
? On-Resistance (R DS(ON) ): The lower, the better.
? Maximum Drain-to-Source Voltage (V DSS ): Should
be at least 20% higher than the input supply rail at
V CS =
0.8V
A CS
the high side MOSFET’s drain.
? Gate Charges (Q g , Q gd , Q gs ): The lower, the better.
P N 2 CC = ( 1 ? OUT ) × I 2 LOAD × R DS ( ON )
V VALLEY = R DS ( ON ) × ( I LOAD ( MAX ) ? ? ? × I LOAD ( MAX ) )
where A CS is the gain of the current-sense amplifier.
A CS is 6.3 for the MAX1953 when ILIM is connected to
GND and 3.5 for the MAX1954/MAX1957, and for the
MAX1953 when ILIM is connected to IN or floating. The
0.8V is the usable dynamic range of COMP (V COMP ).
Initially, the high-side MOSFET is monitored. Once the
voltage drop across the high-side MOSFET exceeds V CS ,
the high-side MOSFET is turned off and the low-side
MOSFET is turned on. The voltage across the low-side
MOSFET is then monitored. If the voltage across the low-
side MOSFET exceeds the short-circuit current limit, a
short-circuit condition is determined and the low-side
MOSFET is held on. Once the monitored voltage falls
below the short-circuit current-limit threshold, the
MAX1953/MAX1954/MAX1957 switch normally. The short-
circuit current-limit threshold is fixed at 210mV for the
MAX1954/ MAX1957 and is selectable for the MAX1953.
When selecting the high-side MOSFET, use the follow-
ing method to verify that the MOSFET’s R DS(ON) is suffi-
ciently low at the operating junction temperature (T J ):
0 . 8 V
R DS ( ON ) N 1 ≤
A CS × I PEAK
The voltage drop across the low-side MOSFET at the
valley point and at I LOAD(MAX) is:
? LIR ?
? 2 ?
where R DS(ON) is the maximum value at the desired
maximum operating junction temperature of the MOS-
For a 3.3V input application, choose a MOSFET with a
rated R DS(ON) at V GS = 2.5V. For a 5V input application,
choose the MOSFETs with rated R DS(ON) at V GS ≤ 4.5V.
For a good compromise between efficiency and cost,
choose the high-side MOSFET (N1) that has conduction
losses equal to switching loss at the nominal input volt-
age and output current. The selected low-side and high-
side MOSFETs (N2 and N1, respectively) must have
R DS(ON) that satisfies the current-limit setting condition
above. For N2, make sure that it does not spuriously turn
on due to dV/dt caused by N1 turning on, as this would
result in shoot-through current degrading the efficiency.
MOSFETs with a lower Q gd /Q gs ratio have higher immu-
nity to dV/dt.
For proper thermal management design, the power dis-
sipation must be calculated at the desired maximum
operating junction temperature, T J(MAX) . N1 and N2
have different loss components due to the circuit oper-
ation. N2 operates as a zero-voltage switch; therefore,
major losses are the channel conduction loss (P N2CC )
and the body diode conduction loss (P N2DC ):
USE R DS ( ON ) AT T J ( MAX )
V
V IN
P N 2 DC = 2 × I LOAD × V F × t DT × f S
where V F is the body diode forward-voltage drop, t dt is
the dead time between N1 and N2 switching transi-
tions, and f S is the switching frequency.
16
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1957EUB+ | 功能描述:电流型 PWM 控制器 High-f Current-Mode PWM Buck Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1957EUB+T | 功能描述:电流型 PWM 控制器 High-f Current-Mode PWM Buck Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1957EUB-T | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX19586ETN | 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| MAX19586ETN+D | 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
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