UC3842N [NXP]
Current-mode PWM controller; 电流模式PWM控制器
| 型号： | UC3842N |
| 厂家： | 
NXP |
| 描述： | Current-mode PWM controller |
| 文件： | 总8页 (文件大小：75K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DESCRIPTION
PIN CONFIGURATIONS
The UC3842 is available in an 8-Pin mini-DIP the necessary
features to implement off-line, fixed-frequency current-mode control
schemes with a minimal external parts count. This technique results
in improved line regulation, enhanced load response characteristics,
and a simpler, easier to design control loop. Topological advantages
include inherent pulse-by-pulse current limiting.
N Package
COMP
1
2
3
4
8
7
6
5
V
V
REF
CC
V
FB
OUTPUT
GROUND
I
SENSE
Protection circuitry includes built-in undervoltage lock-out and
current limiting. Other features include fully-latched operation, a 1%
trimmed bandgap reference, and start-up current less than 1mA.
R
/C
T
T
TOP VIEW
These devices feature a totem-pole output designed to source and
sink high peak current from a capacitive load, such as the gate of a
power MOSFET. Consistent with N-channel power devices, the
output is low in the OFF-state.
D Package
1
2
3
4
5
6
7
14
13
12
11
10
9
V
COMP
NC
REF
NC
FEATURES
V
V
CC
FB
• Low start-up current (≤1mA)
NC
V
C
• Automatic feed-forward compensation
• Pulse-by-pulse current limiting
OUTPUT
I
SENSE
NC
GROUND
8
POWER GROUND
R
/C
T
T
• Enhanced load response characteristics
• Undervoltage lock-out with hysteresis
• Double pulse suppression
TOP VIEW
• High current totem-pole output
APPLICATIONS
• Internally-trimmed bandgap reference
• 400kHz operation, guaranteed min
• Off-line switched mode power supplies
• DC-to-DC converters UC3842
BLOCK DIAGRAM
7(11)
(12)7
V
CC
UVLO
34V
V
REF
8(14)
5.0V
50mA
5V
REF
(9)5
(7)4
S/R
GND
6V
16V
2.5V
INTERNAL
BIAS
OSC
R
/C
T
T
6(10)
OUTPUT
S
ERROR
AMP
2R
+
–
PWM
LATCH
(3)2
(1)1
(5)3
R
V
FB
R
CURRENT
SENSE
1V
COMP
COMPARATOR
CURRENT
SENSE
5(8)
NOTE:
Pin numbers in parentheses refer to the D package.
1100
August 31, 1994
853-0614 13721
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
ORDERING INFORMATION
DESCRIPTION
TEMPERATURE RANGE
0 to +70°C
ORDER CODE
DWG #
0404B
0405B
8-Pin Plastic Dual In-Line Package (DIP)
14-Pin Plastic Small Outline (SO) Package
UC3842N
UC3842D
0 to +70°C
1
ABSOLUTE MAXIMUM RATINGS
SYMBOL
PARAMETER
Supply voltage (I <30mA)
RATING
UNIT
V
V
Self-Limiting
V
CC
CC
Supply voltage
30
CC
(low impedance source)
2, 3
I
Output current
±1
A
µJ
V
OUT
Output energy (capacitive load)
Analog inputs (Pin 2, Pin 3)
Error amp output sink current
5
-0.3 to 6.3
10
1
mA
W
P
Power dissipation at T ≤70°C
A
D
2
(derate 12.5mW/°C for T >70°C)
A
T
T
Storage temperature range
-65 to +150
300
°C
°C
STG
Lead temperature
SOLD
(soldering, 10sec max)
NOTES:
1. All voltages are with respect to Pin 5; all currents are positive into the specified terminal.
2. See section in application note on “Power Dissipation Calculation”.
3. This parameter is guaranteed, but not 100% tested in production.
1101
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DC AND AC ELECTRICAL CHARACTERISTICS
0≤T ≤70°C for UC3842; V =15V; R =10kW; C =3.3nF, unless otherwise specified.
J
CC
T
T
UC3842
Typ
SYMBOL
PARAMETER
TEST CONDITIONS
UNIT
Max
Min
Reference section
V
Output voltage
T =25°C, I =1mA
4.90
5.00
6
5.10
20
V
mV
mV
mV/°C
V
OUT
J
O
Line regulation
Load regulation
12≤V ≤25V
IN
1≤I ≤20mA
6
25
O
1
Temp. stability
0.2
0.4
5.18
1
Total output variation
Line, load, temp.
10Hz≤f≤10kHz, T =25°C
4.82
1
V
NOISE
Output noise voltage
50
5
µV
J
1
Long-term stability
T =125°C, 1000 Hrs.
J
25
mV
mA
mA
Output short-circuit
Output short-circuit
T =25
J
-30
-30
-100
-100
-130
-180
-55<T ≤0°C
J
Oscillator section
Initial accuracy
T =25°C
47
52
0.2
5
57
1
kHz
%
J
Voltage stability
12≤V ≤25V
CC
1
Temp. stability
T
≤T ≤T
J MAX
%
MIN
Amplitude
V
PIN 4
peak-to-peak
1.7
V
Error amp section
Input voltage
V Pin 1=2.5V
2.42
2.50
-0.3
90
2.58
-2
V
µA
dB
I
Input bias current
BIAS
A
VOL
2≤V ≤4V
65
0.7
0.5
60
2
O
1
Unity gain bandwidth
Unity gain bandwidth
Power supply rejection ratio
Output sink current
T =25°C
J
1
MHz
MHz
dB
T
MIN
<T <T
J MAX
PSRR
12≤V ≤25V
70
6
CC
I
V
=2.7V, V =1.1V
PIN 1
mA
mA
V
SINK
PIN 2
I
Output source current
V
=2.3V, V =5V
PIN 1
-0.5
5
-0.8
6
SOURCE
PIN 2
V
OUT
V
OUT
High
Low
V
=2.3V, R =15k to ground
PIN 2 L
V
=2.7V, R =15k to Pin 8
0.7
1.1
V
PIN 2
L
Current sense section
2, 3
Gain
2.85
0.9
3
1
3.15
1.1
V/V
V
2
Maximum input signal
V
PIN 1
=5V
2
PSRR
Power supply rejection ratio
Input bias current
12≤V ≤25V
70
-2
dB
µA
ns
CC
I
-10
BIAS
1
Delay to output
150
300
1102
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DC AND AC ELECTRICAL CHARACTERISTICS
4
0≤T ≤70°C for UC3842; V =15 ; R =10kΩ; C =3.3nF, unless otherwise specified
J
CC
T
T
UC3842
Typ
SYMBOL
PARAMETER
TEST CONDITIONS
UNIT
Min
Max
Output section
I
=20mA
0.1
1.5
13.5
13.5
50
0.4
2.2
SINK
V
V
Output Low-Level
V
V
OL
I
=200mA
SINK
I
=20mA
13
12
SOURCE
Output High-Level
OH
I
=200mA
SOURCE
t
t
Rise time
Fall time
C =1nF
150
150
ns
ns
R
L
C =1nF
50
F
L
Undervoltage lockout section
Start threshold
14.5
8.5
16
10
17.5
11.5
V
V
Min. operating voltage after turn on
PWM section
Maximum duty cycle
Minimum duty cycle
93
97
100
0
%
Total standby current
Start-up current
0.5
11
1
mA
mA
V
I
Operating supply current
V
=V =0V
PIN 3
17
CC
PIN 2
V
CC
zener voltage
I
=25mA
34
CC
Maximum operating frequency section
Maximum operating frequency for all
functions operating cycle-by-cycle
400
kHz
NOTES:
1. These parameters, although guaranteed, are not 100% tested in production.
2. Parameter measured at trip point of latch with V =0.
PIN 2
DVPIN 1
3. Gain defined as:
A +
; 0 v VPIN 3 v 0.8V
DVPIN 3
UNDERVOLTAGE LOCKOUT
ERROR AMP CONFIGURATION
7
2.5V
ON/OFF COMMAND
TO REST OF IC
V
0.5mA
CC
+
Z
I
2
–
V
FB
1
UC3842
16V
COMP
V
V
ON
NOTE:
Error AMP can source or sink up to 0.5mA.
10V
OFF
I
CC
<15mA
<1mA
V
CC
V
V
OFF
ON
NOTE:
During Undervoltage Lock-Out, the output driver is biased to a high
impedance state. Pin 6 should be shunted to ground with a bleeder
resistor to prevent activating the power switch with output leakage current.
1103
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
CURRENT SENSE CIRCUIT
ERROR
AMP
2R
I
S
CURRENT
SENSE
COMPARATOR
R
1V
1
COMP
R
3
CURRENT
SENSE
R
S
5
GND
NOTE:
Peak current (I ) is determined by the formula:
S
1.0V
I
MAX
+
S
R
s
A small RC filter may be required to suppress switch transients.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Saturation Characteristics
Error Amplifier Open-Loop
Frequency Response
4
45
100
80
60
40
20
0
0
0
3
2
1
0
Av
–45
–90
–135
–180
–225
–20
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
0.01
0.03 0.05 0.1
0.3 0.5 1.0
OUTPUT CURRENT, SOURCE OR SINK (A)
1104
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
OPEN-LOOP LABORATORY TEST FIXTURE
V
REF
A
R
T
V
CC
2N2222
100k
4.7k
UC3842
1
8
0.1µF
COMP
V
REF
ERROR AMP
ADJUST
2
7
0.1µF
1k
1W
V
V
FB
3
CC
6
OUTPUT
5k
OUTPUT
5
I
SENSE
4.7k
I
SENSE
ADJUST
4
GND
R
/C
T
T
GND
C
T
NOTE:
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close to Pin 5 in a single point
ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to Pin 3.
SHUTDOWN TECHNIQUES
4.7k
8
1
COMP
3
4.7k
SHUTDOWN
I
SENSE
500
SHUTDOWN
TO CURRENT
SENSE RESISTOR
NOTE:
Shutdown of the UC3842 can be accomplished by two methods; either raise Pin 3 above 1V or pull Pin 1 below a voltage two diode drops above ground. Either method causes the
output of the PWM comparator 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 shutdown
condition at Pins 1 and/or 3 is removed. In the examples shown, an externally-latched shutdown may be accomplished by adding an SCR which will be reset by cycling
V
below the lower UVLO threshold (10V). At this point all internal bias is removed, allowing the SCR to reset.
CC
1105
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
OFF-LINE FLYBACK REGULATOR
T1
USD735
4.7 1W
+
4.7k
4W
0.01µF
220µF
250V
400V
4700µF
DC
OUT
(5V 2–5A)
10V
673-3
56k
1W
1N3613
AC
INPUT
–
1N3613
16V
UC3842
0.01µF
10µF
20V
820pF
V
7
CC
20k
2.5k
2
V
150k
FB
27
6
OUT
UFN432
1
20k
COMP
NOTES:
T1: Coilcraft E-4140-B
Primary – 97 turns
single AWG24
3.6k
3
100pF
Secondary – 4 turns
4 parallel
CUR
SEN
8
1k
V
AWG22
control – 9 turns
–3 parallel AWG28
REF
0.85
10k
470pF
4
R
/C
T
T
0.01µF
0.0047µF
ISOLATION
BOUNDARY
5
GND
SPECIFICATIONS
Input line voltage:
Input frequency:
Switching frequency:
Output power:
NOTE:
90V to 130V
AC
AC
This circuit uses a low-cost feedback scheme in which the DC
voltage developed from the primary-side control winding is sensed
by the UC3842 error amplifier. Load regulation is therefore
dependent on the coupling between secondary and control
windings, and on transformer leakage inductance. For applications
requiring better load regulation, a UC1901 Isolated Feedback
Generator can be used to directly sense the output voltage.
50 or 60Hz
40kHz±10%
25W maximum
5V±5%
Output voltage:
Output current:
2 to 5A
Line regulation:
0.01%/V
*
Load regulation:
Efficiency @ 25 W,
8%/A
V
IN
V
IN
=90V
:
70%
AC
=130V
:
65%
AC
Output short-circuit current:
2.5A average
1106
August 31, 1994
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
SYNCHRONIZATION AND MAXIMUM DUTY CYCLE CLAMP
5V
V
CC
4
8
R
R
A
B
RESET
V
7
CC
7
DISCH
R /C
T
3
T
OUT
UC3842
NE555
4
2
6
TRIG
5
THRESH
GND
GND
1
C
NOTES:
TO OTHER
UC3842s
1.44
2R ) C
f
+
(R
A
B
R
B
D
+
MAX
R
2R
B
A
1107
August 31, 1994
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