UC384XA-BW Current Mode PWM Controller
(UC3842A-BW/
43A-BW/44A-BW/45A-BW)
DESCRIPTION
The UC3842A-BW/43A-BW/44A-BW/45A-BW are fixed frequency current mode PWM
controller. They are specially designed for OFF−Line and DC to DC converter applications
with a minimal external components. Internally implemented circuits include a trimmed
PIN
CONNECTION
(TOP VIEW)
oscillator for precise duty cycle control, a temperature compensated reference, high gain
error amplifier, current sensing comparator, and a high current totempole output ideally
suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout
and current limiting.
The UC3842A-BW and UC3844A-BW have UVLO thresholds of 16 V (on) and 10 V (off). The
corresponding thresholds for the UC3843A-BW/45A-BW are 8.4V (on) and
7.6V (off).
The UC3842A-BW and UC3843A-BW can operate within 100% duty cycle. The UC3844A-BW
and UC3845A-BW can operate within 50% duty cycle.
The UC384XA-BW has Start-Up Current 0.17mA (typ).
The UC384XA-BW are revised UC384XAM and differ by higher Unity Gain bandwidth of Error Amplifier.
FEATURES
•
•
•
•
Low Start-Up and Operating Current
High Current Totem Pole Output
Undervoltage Lockout With Hysteresis
Operating Frequency Up To 500KHz
BLOCK DIAGRAM
(toggle flip flop used only in UC3844, UC3845)
Absolute Maximum Ratings
Characteristic
Supply Voltage (low impedance
source)
Output Current
Input Voltage (Analog Inputs pins 2,3)
Error Amp Output Sink Current
Power Dissipation (T
A
=25
0
C)
Storage Temperature Range
Lead Temperature (soldering 5 sec.)
Symbol
V
CC
I
O
V
I
I
SINK (E.A)
P
O
Tstg
T
L
Value
30
±1
−0.3
to 5.5
10
1
-65 to150
260
Unit
V
A
V
mA
W
o
C
o
C
1
UC384XA-BW Current Mode PWM Controller
(UC3842A-BW/
43A-BW/44A-BW/45A-BW)
Electrical characteristics (*V
CC
=15V, R
T
=10kΩ, C
T
=3.3nF, T
A
=0
0
C to +70
0
C, unless otherwise
specified)
Characteristics
Symbol
Test Condition
Min
Typ
Max
Reference Section
Reference Output Voltage
Line Regulation
Load Regulation
Short Circuit Output Current
Oscillator Section
Oscillation Frequency
Frequency Change with Voltage
Oscillator Amplitude
Error Amplifier Section
Input Bias Current
Input Voltage
Open Loop Voltage Gain
Unity Gain Bandwidth
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
Current Sense Section
Gain
Maximum Input Signal
Supply Voltage Rejection
Input Bias Current
Output Section
Low Output Voltage
High Output Voltage
Rise Time
Fall Time
Undervoltage Lockout Section
Start Theshold
Min. Operating Voltage
(After Turn On)
PWM Section
Max. Duty Cycle
Min. Duty Cycle
Total Standby Current
f
∆f/∆V
CC
V
(OSC)
I
BIAS
V
I(E.A)
A
VOL
UGBW
PSRR
I
SINK
I
SOURCE
V
OH
V
OL
G
V
V
I(MAX)
SVR
I
BIAS
V
OL
V
OH
t
R
t
F
V
TH(ST)
V
OPR(min)
T
J
= 25°C
12V
≤
V
CC
≤
25 V
(peak to peak)
V
FB
=3V
V
pin1
= 2.5V
2V
≤
V
0
≤
4V
T
j
=25
0
C, Note 3
12V
≤
V
CC
≤
25 V
V
pin2
= 2.7V, V
pin1
= 1.1V
V
pin2
= 2.3V, V
pin1
= 5V
V
pin2
= 2.3V, R
L
= 15KΩ to GND
V
pin2
= 2.7V, R
L
= 15KΩ to PIN 8
(Note 1 & 2)
V
pin1
= 5V (Note1)
12V
≤
V
CC
≤
25 V (Note 1)
V
pin3
= 3V
I
SINK
I
SINK
I
SINK
I
SINK
=
=
=
=
20 mA
200 mA
20 mA
200 mA
2.85
0.9
2.42
65
0.5
60
2
-0.5
5.0
47
52
0.05
1.6
-0.1
2.5
90
0.6
70
7
-1.0
6.0
0.8
3.0
1.0
70
-3.0
0.08
1.4
13.5
13.0
45
35
14.5
7.8
8.5
7.0
95
47
16.0
8.4
10
7.6
97
48
1.1
3.15
1.1
-10
0.4
2.2
-2
2.58
57
1.0
KHz
%
V
µA
V
dB
MHz
dB
mA
mA
V
V
REF
∆V
REF
∆V
REF
I
SC
T
J
= 25°C, I
REF
= 1 mA
12V
≤
V
CC
≤
25 V
1 mA
≤
I
REF
≤
20mA
T
A
= 25°C
4.9
5.0
6.0
6.0
-100
5.1
20
25
-180
mA
Unit
V
mV
V/V
V
dB
µA
13
12
V
T
J
= 25°C, C
L
= 1nF (Note 3)
T
J
= 25°C, C
L
= 1nF (Note 3)
UC3842A-BW/44A-BW
UC3843A-BW/45A-BW
UC3842A-BW/44A-BW
UC3843A-BW/45A-BW
UC3842A-BW/43A-BW
UC3844A-BW/45A-BW
150
150
17.5
9.0
11.5
8.2
100
50
0
0.3
17
nS
V
V
D
(MAX)
D
(MAX)
%
UC384XA-BW
I
ST
Start−Up Current
Operating Supply Current
I
CC (OPR)
V
pin3
= V
pin2
= 0V
Zener Voltage
V
Z
I
CC
=25 mA
30
* Adjust V
CC
above the start threshold before setting it to 15V.
Note 1: Parameter measured at trip point of latch with V
pin2
=0.
Note 2: Gain defined as A=∆V
pin1
/∆V
pin3
; 0
≤
V
pin3
≤
0.8V.
Note 3: These parameters, although guaranteed, are not 100% tested in production.
0.17
13
38
mA
V
2
UC384XA-BW Current Mode PWM Controller
(UC3842A-BW/
43A-BW/44A-BW/45A-BW)
PIN FUNCTION
N
1
2
3
4
5
6
7
8
FUNCTION
COMP
V
FB
I
SENSE
R
T
/C
T
GROUND
OUTPUT
V
CC
V
ref
DESCRIPTION
This pin is the Error Amplifier output and is made for loop compensation.
This is the inverting input of the Error Amplifier. It is normally connected to the
switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM
uses this information to terminate the output switch conduction.
The oscillator frequency and maximum Output duty cycle are programmed by
connecting resistor R
T
to V
ref
and capacitor C
T
to ground.
This pin is the combined control circuitry and power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1A
are sourced and sink by this pin.
This pin is the positive supply of the integrated circuit.
This is the reference output. It provides charging current for capacitor C
T
through
resistor R
T
.
APPLICATION INFORMATION
Figure 1. Error Amp Configuration
Figure 2. Undervoltage Lockout
3
UC384XA-BW Current Mode PWM Controller
(UC3842A-BW/
43A-BW/44A-BW/45A-BW)
Figure 3. Current Sense Circuit
Figure 4. Slope Compensation Techniques
4
UC384XA-BW Current Mode PWM Controller
(UC3842A-BW/
43A-BW/44A-BW/45A-BW)
SCR must be selected for a holding current of less than 0.5mA.
The simple two transistor circuit can be used in place of the SCR as shown.
Figure 5. Latched Shutdown
Figure 6. Error Amplifier Compensation
5
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