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TOP232Y 参数 Datasheet PDF下载

TOP232Y图片预览
型号: TOP232Y
PDF下载: 下载PDF文件 查看货源
内容描述: 的TOPSwitch - FX系列设计灵活, EcoSmart® ,集成离线式开关 [TOPSwitch-FX Family Design Flexible, EcoSmart®, Integrated Off-line Switcher]
分类和应用: 开关
文件页数/大小: 36 页 / 644 K
品牌: PAM [ POWER ANALOG MICOELECTRONICS ]
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TOP232-234  
CONTROL pin current, before the CONTROL pin voltage has  
had a chance to discharge to the lower threshold voltage of  
approximately 4.8 V (internal supply under-voltage lockout  
threshold). When the externally fed current charges the  
CONTROL pin to the shunt regulator voltage of 5.8 V, current  
in excess of the consumption of the chip is shunted to SOURCE  
through resistor RE as shown in Figure 2. This current flowing  
through RE controls the duty cycle of the power MOSFET to  
provide closed loop regulation. The shunt regulator has a finite  
low output impedance ZC that sets the gain of the error amplifier  
when used in a primary feedback configuration. The dynamic  
impedance ZC of the CONTROL pin together with the external  
CONTROL pin capacitance sets the dominant pole for the  
control loop.  
Oscillator and Switching Frequency  
Theinternaloscillatorlinearlychargesanddischargesaninternal  
capacitance between two voltage levels to create a sawtooth  
waveformforthepulsewidthmodulator. Theoscillatorsetsthe  
pulse width modulator/current limit latch at the beginning of  
each cycle.  
The nominal switching frequency of 132 kHz was chosen to  
minimize transformer size while keeping the fundamental EMI  
frequency below 150 kHz. The FREQUENCY pin (available  
only in TO-220 package), when shorted to the CONTROL pin,  
lowers the switching frequency to 66 kHz (half frequency)  
which may be preferable in some cases such as noise sensitive  
videoapplicationsorahighefficiencystandbymode. Otherwise,  
theFREQUENCYpinshouldbeconnectedtotheSOURCEpin  
for the default 132 kHz. Trimming of the current reference  
improves oscillator frequency accuracy.  
When a fault condition such as an open loop or shorted output  
preventstheflowofanexternalcurrentintotheCONTROLpin,  
the capacitor on the CONTROL pin discharges towards 4.8 V.  
At4.8Vauto-restartisactivatedwhichturnstheoutputMOSFET  
off and puts the control circuitry in a low current standby mode.  
The high-voltage current source turns on and charges the  
external capacitance again. A hysteretic internal supply under-  
voltage comparator keeps VC within a window of typically 4.8  
to 5.8 V by turning the high-voltage current source on and off  
as shown in Figure 5. The auto-restart circuit has a divide-by-  
8 counter which prevents the output MOSFET from turning on  
again until eight discharge/charge cycles have elapsed. This is  
accomplished by enabling the output MOSFET only when the  
divide-by-8 counter reaches full count (S7). The counter  
effectivelylimitsTOPSwitch-FXpowerdissipationbyreducing  
the auto-restart duty cycle to typically 4%. Auto-restart mode  
continues until output voltage regulation is again achieved  
through closure of the feedback loop.  
To further reduce the EMI level, the switching frequency is  
jittered (frequency modulated) by approximately 4 kHz at  
250 Hz (typical) rate as shown in Figure 6. Figure 28 shows the  
typical improvement of EMI measurements with frequency  
jitter.  
Pulse Width Modulator and Maximum Duty Cycle  
The pulse width modulator implements voltage mode control  
by driving the output MOSFET with a duty cycle inversely  
proportional to the current into the CONTROL pin that is in  
excess of the internal supply current of the chip (see Figure 4).  
The excess current is the feedback error signal that appears  
across RE (see Figure 2). This signal is filtered by an RC  
network with a typical corner frequency of 7 kHz to reduce the  
effectofswitchingnoiseinthechipsupplycurrentgeneratedby  
VUV  
VLINE  
0 V  
S0  
S0  
S7  
S1  
S2  
S6  
S7 S0  
S1  
S2  
S6  
S7  
S1 S2  
S6  
S7  
S7  
5.8 V  
4.8 V  
VC  
0 V  
VDRAIN  
0 V  
VOUT  
0 V  
1
2
3
2
4
Note: S0 through S7 are the output states of the auto-restart counter  
PI-2545-082299  
Figure 5. Typical Waveforms for (1) Power Up (2) Normal Operation (3) Auto-restart (4) Power Down .  
B
7/01  
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