参数资料
| 型号： | UC3843ANG |
| 厂商： | ON Semiconductor |
| 文件页数： | 9/18页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO PWM 8-DIP |
| 产品变化通告： | Product Discontinuation 15/May/2006 |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 96% |
| 电源电压： | 7.6 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： | 8-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
| 其它名称： | UC3843ANGOS |
UC3842A, UC3843A, UC2842A, UC2843A
OPERATING DESCRIPTION
The UC3842A, UC3843A series are high performance,
fixed frequency, current mode controllers. They are
specifically designed for Off?Line and DC?to?DC
converter applications offering the designer a cost effective
solution with minimal external components. A
is removed, or at the beginning of a soft?start interval
(Figures 24, 25). The Error Amp minimum feedback
resistance is limited by the amplifier ’s source current
(0.5 mA) and the required output voltage (V OH ) to reach the
comparator ’s 1.0 V clamp level:
= 8800 W
representative block diagram is shown in Figure 18.
Oscillator
R f(min) ≈
3.0 (1.0 V) + 1.4 V
0.5 mA
I pk =
The oscillator frequency is programmed by the values
selected for the timing components R T and C T . Capacitor C T
is charged from the 5.0 V reference through resistor R T to
approximately 2.8 V and discharged to 1.2 V by an internal
current sink. During the discharge of C T , the oscillator
generates and internal blanking pulse that holds the center
input of the NOR gate high. This causes the Output to be in
a low state, thus producing a controlled amount of output
deadtime. Figure 2 shows R T versus Oscillator Frequency
and Figure 3, Output Deadtime versus Frequency, both for
given values of C T . Note that many values of R T and C T will
give the same oscillator frequency but only one combination
will yield a specific output deadtime at a given frequency.
The oscillator thresholds are temperature compensated, and
the discharge current is trimmed and guaranteed to within
± 10% at T J = 25 ° C. These internal circuit refinements
minimize variations of oscillator frequency and maximum
output duty cycle. The results are shown in Figures 4 and 5.
In many noise sensitive applications it may be desirable to
frequency?lock the converter to an external system clock.
This can be accomplished by applying a clock signal to the
circuit shown in Figure 21. For reliable locking, the
free?running oscillator frequency should be set about 10%
less than the clock frequency. A method for multi unit
synchronization is shown in Figure 22. By tailoring the
Current Sense Comparator and PWM Latch
The UC3842A, UC3843A operate as a current mode
controller, whereby output switch conduction is initiated by
the oscillator and terminated when the peak inductor current
reaches the threshold level established by the Error
Amplifier Output/Compensation (Pin 1). Thus the error
signal controls the peak inductor current on a
cycle?by?cycle basis. The current Sense Comparator PWM
Latch configuration used ensures that only a single pulse
appears at the Output during any given oscillator cycle. The
inductor current is converted to a voltage by inserting the
ground referenced sense resistor R S in series with the source
of output switch Q1. This voltage is monitored by the
Current Sense Input (Pin 3) and compared a level derived
from the Error Amp Output. The peak inductor current under
normal operating conditions is controlled by the voltage at
pin 1 where:
V (Pin 1) ? 1.4 V
3 R S
Abnormal operating conditions occur when the power
supply output is overloaded or if output voltage sensing is
lost. Under these conditions, the Current Sense Comparator
threshold will be internally clamped to 1.0 V. Therefore the
maximum peak switch current is:
clock waveform, accurate Output duty cycle clamping can
be achieved.
I pk(max) =
1.0 V
R S
Error Amplifier
A fully compensated Error Amplifier with access to the
inverting input and output is provided. It features a typical
dc voltage gain of 90 dB, and a unity gain bandwidth of
1.0 MHz with 57 degrees of phase margin (Figure 8). The
noninverting input is internally biased at 2.5 V and is not
pinned out. The converter output voltage is typically divided
down and monitored by the inverting input. The maximum
input bias current is ?2.0 m A which can cause an output
voltage error that is equal to the product of the input bias
current and the equivalent input divider source resistance.
The Error Amp Output (Pin 1) is provide for external loop
compensation (Figure 31). The output voltage is offset by
two diode drops ( ≈ 1.4 V) and divided by three before it
connects to the inverting input of the Current Sense
Comparator. This guarantees that no drive pulses appear at
the Output (Pin 6) when Pin 1 is at its lowest state (V OL ).
When designing a high power switching regulator it
becomes desirable to reduce the internal clamp voltage in
order to keep the power dissipation of R S to a reasonable
level. A simple method to adjust this voltage is shown in
Figure 23. The two external diodes are used to compensate
the internal diodes yielding a constant clamp voltage over
temperature. Erratic operation due to noise pickup can result
if there is an excessive reduction of the I pk(max) clamp
voltage.
A narrow spike on the leading edge of the current
waveform can usually be observed and may cause the power
supply to exhibit an instability when the output is lightly
loaded. This spike is due to the power transformer
interwinding capacitance and output rectifier recovery time.
The addition of an RC filter on the Current Sense Input with
a time constant that approximates the spike duration will
usually eliminate the instability; refer to Figure 27.
This occurs when the power supply is operating and the load
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相关代理商/技术参数 |
参数描述 |
|---|---|
| UC3843ANG4 | 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 |
| UC3843ANMOT | 制造商:ON Semiconductor 功能描述:ADVANCED PWM CONTROLLER 3843 DIP8 |
| UC3843AP-D08-T | 制造商:UTC-IC 制造商全称:UTC-IC 功能描述:CURRENT MODE PWM CONTROL CIRCUITS |
| UC3843AP-S08-R | 制造商:UTC-IC 制造商全称:UTC-IC 功能描述:CURRENT MODE PWM CONTROL CIRCUITS |
| UC3843AP-S08-T | 制造商:UTC-IC 制造商全称:UTC-IC 功能描述:CURRENT MODE PWM CONTROL CIRCUITS |
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