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参数资料
| 型号： | MAX5974AEVKIT# |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 22/27页 |
| 文件大小： | 0K |
| 描述： | EVAL KIT MAX5974A |
| 标准包装： | 1 |
| 系列： | * |
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MAX5974A/MAX5974B/MAX5974C/MAX5974D
Active-Clamped, Spread-Spectrum,
Current-Mode PWM Controllers
Choose a higher value for R IN than the one calculated
above if a longer startup time can be tolerated in order
to minimize power loss on this resistor.
Active Clamp Circuit
Traditional clamp circuits prevent transformer saturation
by channeling the magnetizing current (I M ) of the trans-
former onto a dissipative RC network. To improve effi-
ciency, the active clamp circuit recycles I M between the
magnetizing inductance and clamp capacitor. V CLAMP
is given by:
The AUX driver controls the p-channel FET through a
level shifter. The level shifter consists of an RC network
(formed by C AUX and R AUX ) and diode D5, as shown in
the Typical Application Circuits . Choose R AUX and C AUX
so that the time constant exceeds 100/f SW . Diode D5 is a
small-signal diode with a voltage rating exceeding 25V.
Additionally, C CLAMP should be chosen such that the
complex poles formed with magnetizing inductance
(L MAG ) and C CLAMP are 2x to 4x away from the loop
bandwidth:
V CLAMP =
V S
1 ? D
1-D
2 π L MAG × C CLAMP
> 3 × f BW
V CLAMP(MAX-NORMAL) =
N P × V O
= V OUT × T
V T
1 ? DCLMP
D MAX-FF =
= ? ?
V S
R DCLMP2
=? ×
? 1 ?
?
= V OUT × C
V COUPLED
V CLAMP(MAX-FF) =
2.43 × ( R DCLMP1 + R DCLMP2 )
where V S is the voltage of the power source and D is
the duty cycle. To select n-channel and p-channel FETs
with adequate breakdown voltages, use the maximum
value of V CLAMP . V CLAMP(MAX) occurs when the input
voltage is at its minimum and the duty cycle is at its
maximum. V CLAMP(MAX-NORMAL) during normal opera-
tion is therefore:
V S(MIN)
1 ?
N S × V S(MIN)
where V S(MIN) is the minimum voltage of the power
source, N P /N S is the primary to secondary turns ratio,
and V O is the output voltage. The clamp capacitor,
n-channel, and p-channel FETs must have breakdown
voltages exceeding this level.
If feed-forward maximum duty-cycle clamp is used then:
V MIN ? V ?
2.43 ? 2.43 ?
? ?
2.43 R DCLMP1 + R DCLMP2 ?
Therefore, V CLAMP(MAX-FF) during feed-forward maxi-
mum duty clamp is:
V S
1 ? D MAX ? FF
=
R DCLMP2
22
Bias Circuit
Optocoupler Feedback (MAX5974C/MAX5974D)
An in-phase tertiary winding is needed to power the bias
circuit when using optocoupler feedback. The voltage
across the tertiary V T during the on-time is:
N
N S
where V OUT is the output voltage and N T /N S is the turns
ratio from the tertiary to the secondary winding. Select the
turns ratio so that V T is above the UVLO shutdown level
(7.35V max) by a margin determined by the holdup time
needed to “ride through” a brownout.
Coupled-Inductor Feedback (MAX5974A/MAX5974B)
When using coupled-inductor feedback, the power for
the devices can be taken from the coupled inductor dur-
ing the off-time. The voltage across the coupled induc-
tor, V COUPLED , during the off-time is:
N
N O
where V OUT is the output voltage and N C /N O is the
turns ratio from the coupled output to the main output
winding. Select the turns ratio so that V COUPLED is
above the UVLO shutdown level (7.5V max) by a margin
determined by the holdup time needed to “ride through”
a brownout.
This voltage appears at the input of the devices, less
a diode drop. An RC network consisting of R SNUB and
C SNUB is for damping the reverse recovery transients of
diode D6.
Maxim Integrated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX5974AEVKIT# | 功能描述:电源管理IC开发工具 MAX5974A 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 |
| MAX5974BETE+ | 功能描述:电流型 PWM 控制器 Current-Mode PWM 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 |
| MAX5974BETE+T | 功能描述:电流型 PWM 控制器 Current-Mode PWM 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 |
| MAX5974CETE+ | 功能描述:电流型 PWM 控制器 Current-Mode PWM 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 |
| MAX5974CETE+T | 功能描述:电流型 PWM 控制器 Current-Mode PWM 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 |
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