Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DESCRIPTION
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.
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.
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.
PIN CONFIGURATIONS
N Package
COMP
V
FB
I
SENSE
R
T
/C
T
1
2
3
4
TOP VIEW
8
7
6
5
V
REF
V
CC
OUTPUT
GROUND
D Package
COMP
1
2
3
4
5
6
7
TOP VIEW
14
V
REF
13
NC
12
V
CC
11
V
C
10
OUTPUT
9
8
GROUND
POWER GROUND
FEATURES
NC
V
FB
NC
I
SENSE
NC
R
T
/C
T
•
Low start-up current (≤1mA)
•
Automatic feed-forward compensation
•
Pulse-by-pulse current limiting
•
Enhanced load response characteristics
•
Undervoltage lock-out with hysteresis
•
Double pulse suppression
•
High current totem-pole output
•
Internally-trimmed bandgap reference
•
400kHz operation, guaranteed min
BLOCK DIAGRAM
APPLICATIONS
•
Off-line switched mode power supplies
•
DC-to-DC converters UC3842
7(11)
(12)7
V
CC
34V
(9)5
GND
16V
2.5V
INTERNAL
BIAS
6V
UVLO
S/R
5V
REF
V
8(14)
REF
5.0V
50mA
(7)4
R
T
/C
T
OSC
6(10)
OUTPUT
ERROR
AMP
V
FB
COMP
CURRENT
SENSE
NOTE:
Pin numbers in parentheses refer to the D package.
(3)2
(1)1
(5)3
+
–
S
2R
R
R
1V
CURRENT
SENSE
COMPARATOR
PWM
LATCH
5(8)
August 31, 1994
1100
853-0614 13721
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
ORDERING INFORMATION
DESCRIPTION
8-Pin Plastic Dual In-Line Package (DIP)
14-Pin Plastic Small Outline (SO) Package
TEMPERATURE RANGE
0 to +70°C
0 to +70°C
ORDER CODE
UC3842N
UC3842D
DWG #
0404B
0405B
ABSOLUTE MAXIMUM RATINGS
1
SYMBOL
V
CC
V
CC
I
OUT
PARAMETER
Supply voltage (I
CC
<30mA)
Supply voltage
(low impedance source)
Output current
2, 3
Output energy (capacitive load)
Analog inputs (Pin 2, Pin 3)
Error amp output sink current
P
D
T
STG
T
SOLD
Power dissipation at T
A
≤70°C
(derate 12.5mW/°C for T
A
>70°C)
2
Storage temperature range
Lead temperature
(soldering, 10sec max)
-65 to +150
300
°C
°C
30
±1
5
-0.3 to 6.3
10
1
RATING
UNIT
Self-Limiting
V
A
µJ
V
mA
W
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.
August 31, 1994
1101
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DC AND AC ELECTRICAL CHARACTERISTICS
0≤T
J
≤70°C
for UC3842; V
CC
=15V; R
T
=10kW; C
T
=3.3nF, unless otherwise specified.
SYMBOL
PARAMETER
TEST CONDITIONS
UC3842
Min
Typ
Max
UNIT
Reference section
V
OUT
Output voltage
Line regulation
Load regulation
Temp. stability
1
Total output variation
1
V
NOISE
Output noise voltage
1
Long-term stability
1
Output short-circuit
Output short-circuit
Line, load, temp.
10Hz≤f≤10kHz, T
J
=25°C
T
J
=125°C, 1000 Hrs.
T
J
=25
-55<T
J
≤0°C
T
J
=25°C
12≤V
CC
≤25V
T
MIN
≤T
J
≤T
MAX
V
PIN 4
peak-to-peak
V Pin 1=2.5V
2≤V
O
≤4V
Unity gain bandwidth
1
Unity gain bandwidth
PSRR
I
SINK
I
SOURCE
Power supply rejection ratio
Output sink current
Output source current
V
OUT
High
V
OUT
Low
T
J
=25°C
T
MIN
<T
J
<T
MAX
12≤V
CC
≤25V
V
PIN 2
=2.7V, V
PIN 1
=1.1V
V
PIN 2
=2.3V, V
PIN 1
=5V
V
PIN 2
=2.3V, R
L
=15k to ground
V
PIN 2
=2.7V, R
L
=15k to Pin 8
2.85
V
PIN 1
=5V
12≤V
CC
≤25V
0.9
2.42
-30
-30
4.82
50
5
-100
-100
25
-130
-180
T
J
=25°C, I
O
=1mA
12≤V
IN
≤25V
1≤I
O
≤20mA
4.90
5.00
6
6
0.2
5.10
20
25
0.4
5.18
V
mV
mV
mV/°C
V
µV
mV
mA
mA
Oscillator section
Initial accuracy
Voltage stability
Temp. stability
1
Amplitude
47
52
0.2
5
1.7
57
1
kHz
%
%
V
Error amp section
Input voltage
I
BIAS
A
VOL
Input bias current
65
0.7
0.5
60
2
-0.5
5
70
6
-0.8
6
0.7
1.1
2.50
-0.3
90
1
2.58
-2
V
µA
dB
MHz
MHz
dB
mA
mA
V
V
Current sense section
Gain
2, 3
Maximum input signal
2
PSRR
I
BIAS
Power supply rejection ratio
2
Input bias current
Delay to output
1
3
1
70
-2
150
-10
300
3.15
1.1
V/V
V
dB
µA
ns
August 31, 1994
1102
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
DC AND AC ELECTRICAL CHARACTERISTICS
0≤T
J
≤70°C
for UC3842; V
CC
=15
4
; R
T
=10kΩ; C
T
=3.3nF, unless otherwise specified
SYMBOL
PARAMETER
TEST CONDITIONS
UC3842
Min
Typ
Max
UNIT
Output section
V
OL
V
OH
t
R
t
F
Output Low-Level
Output High-Level
Rise time
Fall time
I
SINK
=20mA
I
SINK
=200mA
I
SOURCE
=20mA
I
SOURCE
=200mA
C
L
=1nF
C
L
=1nF
14.5
8.5
13
12
0.1
1.5
13.5
13.5
50
50
150
150
0.4
2.2
V
V
ns
ns
Undervoltage lockout section
Start threshold
Min. operating voltage after turn on
16
10
17.5
11.5
V
V
PWM section
Maximum duty cycle
Minimum duty cycle
93
97
100
0
%
Total standby current
Start-up current
I
CC
Operating supply current
V
CC
zener voltage
V
PIN 2
=V
PIN 3
=0V
I
CC
=25mA
0.5
11
34
1
17
mA
mA
V
Maximum operating frequency section
Maximum operating frequency for all
functions operating cycle-by-cycle
NOTES:
1. These parameters, although guaranteed, are not 100% tested in production.
2. Parameter measured at trip point of latch with V
PIN 2
=0.
DV
PIN 1
3. Gain defined as:
; 0
v
V
PIN 3
v
0.8V
A
+
DV
PIN 3
400
kHz
UNDERVOLTAGE LOCKOUT
7
V
CC
ON/OFF COMMAND
TO REST OF IC
ERROR AMP CONFIGURATION
2.5V
0.5mA
+
Z
I
2
V
FB
1
–
V
ON
V
OFF
I
CC
UC3842
16V
10V
COMP
NOTE:
Error AMP can source or sink up to 0.5mA.
<15mA
<1mA
V
OFF
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.
V
ON
V
CC
August 31, 1994
1103
Philips Semiconductors Linear Products
Product specification
Current-mode PWM controller
UC3842
CURRENT SENSE CIRCUIT
ERROR
AMP
I
S
2R
CURRENT
SENSE
COMPARATOR
R
1V
1
COMP
R
3
CURRENT
SENSE
R
S
5
GND
NOTE:
Peak current (I
S
) is determined by the formula:
I
S
MAX
+
1.0V
Rs
A small RC filter may be required to suppress switch transients.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Saturation Characteristics
4
100
SATURATION VOLTAGE (V)
VOLTAGE GAIN (dB)
80
0
60
40
20
0
–20
0
0.01
0.03 0.05 0.1
0.3 0.5 1.0
OUTPUT CURRENT, SOURCE OR SINK (A)
10
100
1k 10k 100k 1M
FREQUENCY (Hz)
PHASE (DEG)
Av
–45
–90
–135
–180
–225
10M
Error Amplifier Open-Loop
Frequency Response
45
0
3
2
1
August 31, 1994
1104
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