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UC2845B 데이터시트 PDF




ST Microelectronics에서 제조한 전자 부품 UC2845B은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.


PDF 형식의 UC2845B 자료 제공

부품번호 UC2845B 기능
기능 (UC2842B - UC2845B) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
제조업체 ST Microelectronics
로고 ST Microelectronics 로고


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UC2845B 데이터시트, 핀배열, 회로
UC2842B/3B/4B/5B
® UC3842B/3B/4B/5B
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
. TRIMMED OSCILLATOR FOR PRECISE FRE-
QUENCY CONTROL
. OSCILLATOR FREQUENCY GUARANTEED
AT 250kHz
. CURRENT MODE OPERATION TO 500kHz
. AUTOMATIC FEED FORWARD COMPENSA-
TION
. LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
. INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
. HIGH CURRENT TOTEM POLE OUTPUT
. UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
. LOW START-UP AND OPERATING CURRENT
Minidip
SO8
comparatorwhich alsoprovidescurrent limit control,
and a totem pole output stage designed to source
or sink high peakcurrent. The outputstage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
DESCRIPTION
Differences between members of this family are the
under-voltagelockout thresholds and maximum duty
TheUC384xB family ofcontrolICs providesthe nec- cycle ranges. The UC3842B and UC3844B have
essary features to implement off-line or DC to DC UVLO thresholds of 16V (on) and 10V (off), ideally
fixed frequency current mode control schemes wwwwit.DhataSheet4Us.cuomitedoff-lineapplicationsThecorrespondingthresh-
a minimal external parts count. Internally imple- oldsforthe UC3843BandUC3845Bare8.5 V and7.9
mented circuits include a trimmed oscillator for pre- V. The UC3842B and UC3843B can operate to duty
cise DUTY CYCLE CONTROL under voltage lock- cycles approaching 100%. A range of the zero to <
outfeaturingstart-up current less than0.5mA,a pre- 50 % is obtained by the UC3844B and UC3845B by
cision reference trimmed for accuracy at the error the addition of an internal toggle flip flopwhich blanks
amp input, logicto insure latched operation,a PWM the output off every otherclock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
7
Vi
5
GROUND
4
RT/CT
VFB
COMP
CURRENT
SENSE
2
1
3
34V UVLO
S/R
5V
REF
2.50V
OSC
VREF GOOD
LOGIC
INTERNAL
BIAS
T
8 VREF
5V 50mA
6
OUTPUT
ERROR AMP.
+
-
2R
R
S
R
1V
CURRENT
SENSE
COMPARATOR
PWM
LATCH
UC3842B
D95IN331
March 1999
1/15




UC2845B pdf, 반도체, 판매, 대치품
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ELECTRICAL CHARACTERISTICS (continued)
Symbo l
P a ram et er
OUTPUT SECTION
VOL Output Low Level
Test Conditions
ISINK = 20mA
ISINK = 200mA
UC284XB
UC384XB
Un it
Min . Typ . Max. Min. T yp. Max.
0.1 0.4
1.6 2.2
0.1 0.4
1.6 2.2
V
V
VOH Output High Level
VOLS UVLO Saturation
ISOURCE = 20mA
ISOURCE = 200mA
VCC = 6V; ISINK = 1mA
13 13.5
12 13.5
0.1 1.1
13 13.5
12 13.5
0.1 1.1
V
V
V
tr Rise Time
Tj = 25°C CL = 1nF (2)
tf Fall Time
Tj = 25°C CL = 1nF (2)
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold
X842B/4B
50 150
50 150
50 150
50 150
ns
ns
15 16 17 14.5 16 17.5 V
X843B/5B
7.8 8.4 9.0 7.8 8.4 9.0 V
Min Operating Voltage
After Turn-on
X842B/4B
X843B/5B
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
X842B/3B
94 96 100 94 96 100 %
X844B/5B
47 48 50 47 48 50 %
Minimum Duty Cycle
0 0%
TOTAL STANDBY CURRENT
Ist Start-up Current
Vi = 6.5V for UCX843B/45B
0.3 0.5
0.3 0.5 mA
Vi = 14V for UCX842B/44B
0.3 0.5
0.3 0.5 mA
Ii Operating Supply Current VPIN2 = VPIN3 = 0V
Viz Zener Voltage
Ii = 25mA
12 17
12 17 mA
30 36
30 36
V
Notes :
1. Max package power dissipation limits must be respected; low duty cycle pulse techniques are used during test maintain Tj as
close to Tamb as possible.
2. These parameters, although guaranteed, are not 100% tested in production.
3. Parameter measured at trip point of latch with V PIN2 = 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.
4/15

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UC2845B 전자부품, 판매, 대치품
Figure 10: Output Saturation Voltagevs. Load
Current.
Vsat
D95IN341
(V)
Vi
Source Saturation
(Load to Ground)
-1 TA=25°C
TA=-40°C
-2
Vi=15V
80µs Pulsed Load 120Hz Rate
3
2 TA=-40°C
TA=25°C
1
Sink Saturation
GND
(Load to Vi)
0
0 200 400 600 IO(mA)
Figure 12: Output Waveform.
90%
Vi =15V
CL = 1.0nF
TA = 25°C
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
Figure 11: Supply Current vs. Supply Voltage.
Ii
(mA)
D95IN342
20
15
10
RT=10K
CT=3.3nF
VFB=0V
ISense=0V
5 TA=25°C
0
0
10 20 30
Figure 13: Output Cross Conduction
Vi(V)
Vi =30V
CL = 15pF
TA = 25°C
VO
20V/DIV
10%
50ns/DIV
Figure 14: Oscillator and Output Waveforms.
ICC
100ns/DIV
100mA/DIV
Vi
7
8
5V REG
PWM
RT
CLOCK
4
OSCILLATOR
ID
CT
5
GND
CT
OUTPUT
6
OUTPUT
LARGE RT/SMALL CT
CT
OUTPUT
SMALL RT/LARGE CT
D95IN344
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