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PDF UC2843B Data sheet ( Hoja de datos )
| Número de pieza | UC2843B | |
| Descripción | (UC2842B / UC2843B) HIGH PERFORMANCE CURRENT MODE CONTROLLERS | |
| Fabricantes | ON Semiconductor | |
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UC3842B, UC3843B,
UC2842B, UC2843B,
NCV3843BV
High Performance
Current Mode Controllers
The UC3842B, UC3843B 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. These
integrated circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain error
amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle–by–cycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8–pin dual–in–line and surface
mount (SO–8) plastic package as well as the 14–pin plastic surface
mount (SO–14). The SO–14 package has separate power and ground
pins for the totem pole output stage.
The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off–line converters. The UCX843B is tailored for
lower voltage applications having UVLO thresholds of w8w.w5.DVataS(hoeent4)U.aconmd
7.6 V (off).
• Trimmed Oscillator for Precise Frequency Control
• Oscillator Frequency Guaranteed at 250 kHz
• Current Mode Operation to 500 kHz
• Automatic Feed Forward Compensation
• Latching PWM for Cycle–By–Cycle Current Limiting
• Internally Trimmed Reference with Undervoltage Lockout
• High Current Totem Pole Output
• Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
VCC 7(12)
Vref
8(14)
RT/CT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
-
Error
Amplifier
Latching
PWM
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO-14 package.
Figure 1. Simplified Block Diagram
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
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8
1
8
1
PDIP–8
N SUFFIX
CASE 626
SO–8
D1 SUFFIX
CASE 751
14
1
SO–14
D SUFFIX
CASE 751A
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
8 Vref
7 VCC
6 Output
5 Gnd
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC 4
Current Sense 5
NC 6
RT/CT 7
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
8 Power Ground
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 16 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 17 of this data sheet.
© Semiconductor Components Industries, LLC, 2001
December, 2001 – Rev. 3
1
Publication Order Number:
UC3842B/D
1 page  
2.55 V
2.50 V
UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV
VCC = 15 V
AV = -1.0
TA = 25°C
3.0 V
2.5 V
VCC = 15 V
AV = -1.0
TA = 25°C
2.45 V
0.5 µs/DIV
Figure 6. Error Amp Small Signal
Transient Response
2.0 V
1.0 µs/DIV
Figure 7. Error Amp Large Signal
Transient Response
100 0
VCC = 15 V
80
Gain
VO = 2.0 V to 4.0 V
RL = 100 K
30
TA = 25°C
60 60
40 90
Phase
20 120
0 150
-Ă20
10
180
100 1.0 k 10 k 100 k 1.0 M 10 M
f, FREQUENCY (Hz)
Figure 8. Error Amp Open Loop Gain and
Phase versus Frequency
1.2
VCC = 15 V
1.0
0.8 TA = 25°C
0.6
TA = 125°C
0.4 TA = -55°C
0.2
0
0 2.0 4.0 6.0 8.0
VO, ERROR AMP OUTPUT VOLTAGE (V)
Figure 9. Current Sense Input Threshold
versus Error Amp Output Voltage
0
ÄÄÄÄVCC = 15 V
-Ă4.0
-Ă8.0
ÄÄÄ-12
ÄÄÄÄ ÄÄÄTA=125°C
-16
TA = -55°C
ÄÄÄÄÄÄÄÄÄÄÄÄ-Ă20 TA=25°C
-Ă24
0
20 40 60 80 100 120
Iref, REFERENCE SOURCE CURRENT (mA)
Figure 10. Reference Voltage Change
versus Source Current
110 VCC = 15 V
ÄÄÄÄÄÄRL ≤ 0.1 Ω
90
70
50
-Ă55
-Ă25
0
25 50 75 100 125
TA, AMBIENT TEMPERATURE (°C)
Figure 11. Reference Short Circuit Current
versus Temperature
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5
5 Page 
UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV
(A)
∆I
Control Voltage
Inductor
Current
m1 m2
Dl
)
Dl
m2
m1
Oscillator Period
Dl
)
Dl
mm21ĂĂĂ
m2
m1
t0 t1 t2
Control Voltage
(B)
m3
∆I
m1
m2
Oscillator Period
t4 t5
t3
Inductor
Current
t6
Figure 20. Continuous Current Waveforms
Vref
8(14)
RT
R
Bias
R
External
Sync
Input
CT
0.01
47
4(7)
2(3)
Osc
+
EA
2R
R
1(1)
The diode clamp is required if the Sync amplitude is large enough to cause the bottom
side of CT to go more than 300 mV below ground.
5(9)
Figure 21. External Clock Synchronization
VCC
7(12)
Vin
RA
8
RB
6
5.0k
5 5.0k
2
C 5.0k
1
4
R
Q
S
MC1455
8(14)
3
4(7)
7
2(3)
1(1)
R
Bias
R
Osc
+
EA
2R
R
8(14)
4(7)
R2
2(3)
1(1)
R1
R
Bias
R
5.0V Ref
+
-
Osc
+
1.0 mA
VClamp
EA
2R
R
1.0V
S
Q
R
Comp/Latch
5(9)
+
-
7(11)
6(10)
5(8)
3(5)
fĂ
+Ă
(RAĂ
1.44
)Ă 2RB)C
D(max)
Ă+Ă
RA
RB
Ă)Ă
2RB
To Additional
UCX84XBs
ǒ Ǔ ǒ Ǔ5(9)
VClamp ≈
1.67
R2
R1
)
1
+ 0.33x10-3
R1R2
R1 ) R2
Where: 0 ≤ VClamp ≤ 1.0 V
Ipk(max)Ă
[Ă
VClamp
RS
Q1
RS
Figure 22. External Duty Cycle Clamp and
Multi–Unit Synchronization
Figure 23. Adjustable Reduction of Clamp Level
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11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet UC2843B.PDF ] | |
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