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UC2844 데이터시트 PDF




ST Microelectronics에서 제조한 전자 부품 UC2844은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.


 

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부품번호 UC2844 기능
기능 CURRENTMODE PWM CONTROLLER
제조업체 ST Microelectronics
로고 ST Microelectronics 로고


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UC2844 데이터시트, 핀배열, 회로
UC2842/3/4/5
® UC3842/3/4/5
CURRENT MODE PWM CONTROLLER
. OPTIMIZED FOR OFF-LINE AND DC TO DC
CONVERTERS
. LOW START-UP CURRENT (< 1 mA)
. AUTOMATIC FEED FORWARD COMPENSA-
TION
. PULSE-BY-PULSE CURRENT LIMITING
. ENHANCED LOAD RESPONSE CHARAC-
TERISTICS
. UNDER-VOLTAGE LOCKOUT WITH HYSTER-
ESIS
. DOUBLE PULSE SUPPRESSION
. HIGH CURRENT TOTEM POLE OUTPUT
. INTERNALLY TRIMMED BANDGAP REFER-
ENCE
. 500 KHz OPERATION
. LOW RO ERROR AMP
DESCRIPTION
TheUC3842/3/4/5family of controlICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal externalparts count.Internallyimple-
mentedcircuits include undervoltagelockout featur-
ing start-up current less than 1 mA, a precision ref-
erence trimmed for accuracy at the error amp input,
Minidip
SO14
logic to insure latched operation, a PWM compara-
torwhich also providescurrentlimit control,and a to-
tem pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-Channel MOSFETs, is low in theoff-state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The UC3842 and UC3844 have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding
thresholds for the UC3843 and UC3845 are 8.5 V
and 7.9 V. The UC3842 and UC3843 can operate
to duty cycles approaching 100%. A range of the
zero to < 50 % is obtained by the UC3844 and
UC3845 by the additionof an internal toggle flip flop
which blanks the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845)
October 1998
1/11




UC2844 pdf, 반도체, 판매, 대치품
UC2842/3/4/5-UC3842/3/4/5
ELECTRICAL CHARACTERISTICS (continued)
Symbo l
Ist
Ii
Viz
Parameter
Test Conditions
UC284X
UC384X
Unit
Min. T yp. Max. Min. T yp. Max.
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold
X842/4
15 16 17 14.5 16 17.5 V
X843/5
7.8 8.4 9.0 7.8 8.4 9
V
Min Operating Voltage
After Turn-on
X842/4
X843/5
9 10 11 8.5 10 11.5
7.0 7.6 8.2 7.0 7.6 8.2
V
V
PWM SECTION
Maximum Duty Cycle
X842/3
93 97 100 93 97 100 %
X844/5
46 48 50 47 48 50 %
Minimum Duty Cycle
0 0%
TOTAL STANDBY CURRENT
Start-up Current
0.5 1
0.5 1 mA
Operating Supply Current
Zener Voltage
VPIN2 = VPIN3 = 0V
Ii = 25mA
11 20
34
11 20 mA
34 V
N otes :
2. These parameters, although guaranteed, are not 100% tested in production.
3. Parameter measured at trip point of latch with VPIN2 = 0.
4. Gain defined as :
A = VPIN1 ; 0 VPIN3 0.8 V
VPIN3
5. Adjust Vi above the start threshold before setting at 15 V.
6. Output frequency equals oscillator frequency for the UC3842 and UC3843.
Output frequency is one half oscillator frequency for the UC3844 and UC3845.
4/11

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UC2844 전자부품, 판매, 대치품
Figure 9 : Open Loop Test Circuit.
UC2842/3/4/5-UC3842/3/4/5
High peak currents associatedwith capacitive loads
necessitate careful grounding techniques. Timing
and bypass capacitors should be connected close
Figure 10 : Shutdown Techniques.
to pin 5 in a single point ground. The transistor and
5 Kpotentiometerareused to sampletheoscillator
waveform and apply an adjustable ramp to pin 3.
Shutdown of the UC2842 can be accomplished by
two methods; either raise pin 3 above1V or pull pin
1 below a voltage two diode drops above ground.
Either method cause the output of the PWM com-
parator to be high (refer to block diagram). The
PWM latch is reset dominant so that the output will
remain low until the next clock cycle after the shut-
down conditionat pins 1 and/or3 is removed. In one
example, an externally latched shutdown may be
accomplishedby addingan SCR which will be reset
by cycling Vi belowthe lowerUVLOthreshold.At this
point the referenceturns off, allowing the SCR to re-
set.
7/11

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