参数资料
型号: MC33025
厂商: Motorola, Inc.
英文描述: High Speed Double-Ended PWM Controller
中文描述: 高速双端PWM控制器
文件页数: 9/20页
文件大小: 516K
代理商: MC33025
MC34025 MC33025
9
MOTOROLA ANALOG IC DEVICE DATA
Undervoltage Lockout
There are two undervoltage lockout circuits within the IC.
The first senses VCC and the second Vref. During power–up,
VCC must exceed 9.2 V and Vref must exceed 4.2 V before
the outputs can be enabled and the Soft–Start latch released.
If VCC falls below 8.4 V or Vref falls below 3.6 V, the outputs
are disabled and the Soft–Start latch is activated. When the
UVLO is active, the part is in a low current standby mode
allowing the IC to have an off–line bootstrap start–up circuit.
Typical start–up current is 500
μ
A.
Output
The MC34025 has two high current totem pole outputs
specifically designed for direct drive of power MOSFETs.
They are capable of up to
±
2.0 A peak drive current with a
typical rise and fall time of 30 ns driving a 1.0 nF load.
Separate pins for VC and Power Ground are provided.
With proper implementation, a significant reduction of
switching transient noise imposed on the control circuitry is
possible. The separate VC supply input also allows the
designer added flexibility in tailoring the drive voltage
independent of VCC.
Reference
A 5.1 V bandgap reference is pinned out and is trimmed to
an initial accuracy of
±
1.0% at 25
°
C. This reference has short
circuit protection and can source in excess of 10 mA for
powering additional control system circuitry.
Design Considerations
Do not attempt to construct the converter on
wire–wrap or plug–in prototype boards.
With high
frequency, high power, switching power supplies it is
imperative to have separate current loops for the signal paths
and for the power paths. The printed circuit layout should
contain a ground plane with low current signal and high
current switch and output grounds returning on separate
paths back to the input filter capacitor. All bypass capacitors
and snubbers should be connected as close as possible to
the specific part in question. The PC board lead lengths must
be less than 0.5 inches for effective bypassing or snubbing.
Instabilities
In current mode control, an instability can be encountered
at any given duty cycle. The instability is caused by the
current feedback loop. It has been shown that the instability is
caused by a double pole at half the switching frequency. If an
external ramp (Se) is added to the on–time ramp (Sn) of the
current–sense waveform, stability can be achieved (see
Figure 20).
One must be careful not to add too much ramp
compensation. If too much is added, the system will start to
perform like a voltage mode regulator. All benefits of current
mode control will be lost. Figures 28A and 28B show
examples of two different ways in which external ramp
compensation can be implemented.
1.25 V
+
+
Ramp Input
Current Signal
Sn
Ramp Compensation
Se
Figure 20. Ramp Compensation
A simple equation can be used to calculate the amount of
external ramp necessary to add that will achieve stability in
the current loop. For the following equations, the calculated
values for the application circuit in Figure 36 are also shown.
Se
VO
L
NS
NP
(RS)Ai
where:
= DC output voltage
= number of power transformer primary
=
or secondary turns
= gain of the current sense network
=
(see Figures 25, 26 and 27)
= output inductor
= current sense resistance
VO
NP, NS
Ai
L
RS
0.115 V
μ
s
For the application circuit: Se
5
1.8
μ
4
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相关代理商/技术参数
参数描述
MC33025DW 功能描述:电流型 PWM 控制器 Dual Output Voltage 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
MC33025DWG 功能描述:电流型 PWM 控制器 Dual Output Voltage or Current Mode PWM 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
MC33025DWR2 功能描述:电流型 PWM 控制器 Dual Output Voltage 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
MC33025DWR2G 功能描述:电流型 PWM 控制器 Dual Output Voltage or Current Mode PWM 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
MC33025P 功能描述:电流型 PWM 控制器 Dual Output Voltage 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