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PDF UC3842A Data sheet ( Hoja de datos )
| Número de pieza | UC3842A | |
| Descripción | (UC3842A / UC3843A) HIGH PERFORMANCE CURRENT MODE CONTROLLERS | |
| Fabricantes | Motorola Semiconductors | |
| Logotipo |  |
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Order this document by UC3842A/D
High Performance
Current Mode Controllers
The UC3842A, UC3843A series of high performance fixed frequency
current mode controllers 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 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 UCX842A has UYLO thresholds of 16 V (on) and 10 V (off), ideally
suited for off–line converters. The UCX843A is tailored for lower voltage
applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).
• Trimmed Oscillator Discharge Current for Precise Duty Cycle Control
• 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
• Direct Interface with Motorola SENSEFET Products
Vref
8(14)
RTCT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
Simplified Block Diagram
VCC 7(12)
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.
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
UC3842A, 43A
UC2842A, 43A
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
8
1
14
1
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
Device
Operating
Temperature Range
Package
UC3842AD
SO–14
UC3843AD
UC3842AN
TA = 0° to +70°C
SO–14
Plastic
UC3843AN
Plastic
UC2842AD
SO–14
UC2843AD
TA = – 25° to +85°C
UC2842AN
SO–14
Plastic
UC2843AN
Plastic
MOTOROLA ANALOG IC DEVICE DATA
© Motorola, Inc. 1996
Rev 1
1
1 page  
UC3842A, 43A UC2842A, 43A
Figure 7. Error Amp Open Loop Gain and
Phase versus Frequency
100 0
VCC = 15 V
80
Gain
VO = 2.0 V to 4.0 V
RL = 100 K
TA = 25°C
30
60 60
40 90
Phase
20 120
0
– 20
10
150
180
100 1.0 k 10 k 100 k 1.0 M 10 M
f, FREQUENCY (Hz)
Figure 8. Current Sense Input Threshold
versus Error Amp Output Voltage
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)
0
–4.0
–8.0
–12
–16
–20
–24
0
Figure 9. Reference Voltage Change
versus Source Current
VCC = 15 V
TA = 125°C
TA = 55°C
TA = 25°C
20 40 60 80 100
Iref, REFERENCE SOURCE CURRENT (mA)
120
Figure 10. Reference Short Circuit Current
versus Temperature
110
VCC = 15 V
RL ≤ 0.1 Ω
90
70
50
–55 –25 0 25 50 75 100 125
TA, AMBIENT TEMPERATURE (°C)
Figure 11. Reference Load Regulation
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
Figure 12. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
2.0 ms/DIV
MOTOROLA ANALOG IC DEVICE DATA
2.0 ms/DIV
5
5 Page 
UC3842A, 43A UC2842A, 43A
Figure 20. External Clock Synchronization
Vref
8(14)
RT
R
Bias
R
External
Sync
Input
0.01
CT
4(7)
47 2(3)
1(1)
Osc
+
+
–
EA
2R
R
5(9)
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.
Figure 21. External Duty Cycle Clamp and
Multi Unit Synchronization
RA
8
4
RB
6
5.0k
+
–
R
5Q
2
+
–
S
C 5.0k MC1455
1
3
7
f=
1.44
(RA + 2RB)C
Dmax =
RB
RA + 2RB
8(14) R
Bias
R
Osc
4(7) +
+
–
2(3) EA
2R
R
1(1)
To Additional
UCX84XA’s
5(9)
Figure 22. Adjustable Reduction of Clamp Level
VCC
7(12)
Vin
8(14)
4(7)
R2
2(3)
1(1)
R1
R
Bias
R
Osc
+
+
–
EA
1.0mA
2R
R
5.0Vref
+ +–
–
+
–+
–
VClamp
–+
1.0V
S
RQ
Comp/Latch
5(9)
7(11)
Q1
6(10)
5(8)
3(5)
RS
VClamp =
1.67
R2 + 1
R1
+ 0.33 x 10 – 3
R1 R2
R1 + R2
Ipk(max) =
VClamp
RS
Where: 0 ≤ VClamp ≤ 1.0 V
Figure 23. Soft–Start Circuit
8(14) R
Bias
R
5.0Vref
+ +–
Osc
4(7) +
–
2(3)
1.0M
+
–
EA
1.0mA
2R
R
–+
1.0V
C 1(1)
tSoft–Start 3600C in µF
5(9)
S
RQ
Figure 24. Adjustable Buffered Reduction of
Clamp Level with Soft–Start
VCC
7(12)
Vin
8(14) R
5.0Vref
+– +
Bias
R
+ +–
–
7(11)
–
Osc
Q1
4(7)
2(3)
R2
1(1)
+
+ 1.0mA
–
EA
2R
R
VClamp
–+
1.0V
S
RQ
Comp/Latch
6(10)
5(8)
3(5)
RS
C MPSA63
R1 1.67
VClamp =
R2 + 1
R1
5(9)
Ipk(max) =
VClamp
RS
tSoftstart = – In
Where: 0 ≤ VClamp ≤ 1.0 V
1–
VC
3VClamp
C
R1 R2
R1 + R2
Figure 25. Current Sensing Power MOSFET
5.0Vref
+ +–
–
VCC
(12)
+– +
–
(11)
Vin
VPin 5
=
RS Ipk rDS(on)
rDM(on) + RS
If: SENSEFET = MTP10N10M
RS = 200
Then: Vpin 5 = 0.075 Ipk
D SENSEFET
S
S
–+ R Q
Comp/Latch
Control CIrcuitry
Ground:
To Pin (9)
(10) G M
(8)
(5) RS
1/4 W
K
Power Ground
To Input Source
Return
Virtually lossless current sensing can be achieved with the implementation of a
SENSEFET power switch. For proper operation during over current conditions, a
reduction of the Ipk(max) clamp level must be implemented. Refer to Figures 22 and 24.
MOTOROLA ANALOG IC DEVICE DATA
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet UC3842A.PDF ] | |
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