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| 型号： | UC3842ADR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 11/18页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO CM 14SOIC |
| 产品变化通告： | Product Discontinuation 15/May/2006 |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 96% |
| 电源电压： | 10 V ~ 30 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 14-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | UC3842ADR2GOS |
UC3842A, UC3843A, UC2842A, UC2843A
DESIGN CONSIDERATIONS
Do not attempt to construct the converter on
wire?wrap or plug?in prototype boards. High Frequency
circuit layout techniques are imperative to prevent pulse
width jitter. This is usually caused by excessive noise
pick?up imposed on the Current Sense or Voltage Feedback
inputs. Noise immunity can be improved by lowering circuit
impedances at these points. 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. Ceramic
bypass capacitors (0.1 m F) connected directly to V CC , V C ,
and V ref may be required depending upon circuit layout.
This provides a low impedance path for filtering the high
frequency noise. All high current loops should be kept as
short as possible using heavy copper runs to minimize
radiated EMI. The Error Amp compensation circuitry and
the converter output voltage divider should be located close
(t 3 ) decreases to ( D I + D I m 2 /m 1 ) (m 2 /m 1 ). This perturbation
is multiplied by m 2 .m 1 on each succeeding cycle, alternately
increasing and decreasing the inductor current at switch
turn?on. Several oscillator cycles may be required before
the inductor current reaches zero causing the process to
commence again. If m 2 /m 1 is greater than 1, the converter
will be unstable. Figure 20B shows that by adding an
artificial ramp that is synchronized with the PWM clock to
the control voltage, the D I perturbation will decrease to zero
on succeeding cycles. This compensation ramp (m 3 ) must
have a slope equal to or slightly greater than m 2 /2 for
stability. With m 2 /2 slope compensation, the average
inductor current follows the control voltage yielding true
current mode operation. The compensating ramp can be
derived from the oscillator and added to either the Voltage
Feedback or Current Sense inputs (Figure 33).
D I + D I m
to the IC and as far as possible from the power switch and
other noise generating components.
Current mode converters can exhibit subharmonic
oscillations when operating at a duty cycle greater than 50%
with continuous inductor current. This instability is
independent of the regulators closed?loop characteristics
and is caused by the simultaneous operating conditions of
Control Voltage
m1
Inductor
Current
t 0
D I
m2
D I + D I m 2
m 1
Oscillator Period
t 1
(A)
t 2
m 2
1
m 2
m 1
t 3
fixed frequency and peak current detecting. Figure 20A
shows the phenomenon graphically. At t 0 , switch
conduction begins, causing the inductor current to rise at a
slope of m 1 . This slope is a function of the input voltage
divided by the inductance. At t 1 , the Current Sense Input
reaches the threshold established by the control voltage.
Control Voltage
D I
m1
m3
(B)
This causes the switch to turn off and the current to decay at
a slope of m 2 until the next oscillator cycle. The unstable
condition can be shown if a perturbation is added to the
m2
Oscillator Period
Inductor
Current
control voltage, resulting in a small D I (dashed line). With
t 4
t5
t 6
a fixed oscillator period, the current decay time is reduced,
and the minimum current at switch turn?on (t 2 ) is increased
by D I + D I m2/m1. The minimum current at the next cycle
Figure 20. Continuous Current Waveforms
http://onsemi.com
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| UC3842ADT | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Current-Mode SMPS Controller |
| UC3842ADTR | 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 |
| UC3842ADTRG4 | 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 |
| UC3842ADW | 功能描述:电流型 PWM 控制器 Current Mode 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 |
| UC3842ADWG4 | 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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