Replacement of
UC3842A/43A/44A/45A-BW
MIK3842A/43A/44A/45A-BW
High Performance Current
Mode PWM Controller
July 2002
Description
The MIK3842A-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
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 MIK3842A-BW and MIK3844A-BW have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding
thresholds for the MIK3843A-BW/45A-BW are 8.4V (on) and 7.6V (off). The MIK3842A-BW and MIK3843A-BW can operate within 100%
duty cycle. The MIK3844A-BW and MIK3845A-BW can operate within 50% duty cycle. The MIK384XA-BW has Start-Up Current 0.17mA
(typ). The MIK384XA-BW are revised MIK384XAM 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
Pin Connection
Top view
Block diagram
(toggle flip flop used only in MIK3844, MIK3845)
7
POWER V
CC
OUT
POWER GND
OSCILLATOR
5
36V
GND
7
V
CC
2
8
V
REF
INTERNAL
BIAS
LOGIC
5V
V
REF
SET/
RESET
6
1
+
-
5
4
R /C
T
T
CURRENT
SENSE
COMP
T
R
1/2 V
REF
1V
C.S.
COMP
ERR
AMP
V
FB
S
PWM
LATCH
3
UVLO
V
GOOD
REF
2R
R
Absolute Maximum Ratings
Symbol Parameter Maximum
Units
V
CC
Supply Voltage (low impedance source)
30
V
I
O
Output
Current
1
A
V
I
Input Voltage (Analog Inputs pins 2,3)
-0.3 to 5.5
V
I
SINK (E.A)
Error Amp Output Sink Current
10
mA
P
O
Power Dissipation (T
A
=25
0
C) 1
W
Tstg
Storage Temperature Range
-65 to150
o
C
T
L
Lead Temperature (soldering 5 sec.)
260
o
C
Page 1 of 8
Replacement of
UC3842A/43A/44A/45A-BW
MIK3842A/43A/44A/45A-BW
High Performance Current
Mode PWM Controller
July 2002
Electrical characteristics
(*V
CC
=15V, R
T
=10k
, C
T
=3.3nF, T
A
=0
0
C to +70
0
C, unless otherwise specified)
Characteristics Symbol
Test
Condition
Min
Typ
Max
Units
Reference Section
Reference Output Voltage
V
REF
T
J
= 25
C, I
REF
= 1 mA
4.9 5.0 5.1 V
Line Regulation
V
REF
12V V
CC
25 V
6.0
20
Load Regulation
V
REF
1 mA I
REF
20mA
6.0
25
mV
Short Circuit Output Current
I
SC
T
A
= 25
C
-100
-180
mA
Oscillator Section
Oscillation Frequency
f
T
J
= 25
C
47 52 57 KHz
Frequency Change with Voltage
f/V
CC
12V V
CC
25 V
0.05
1.0
%
Oscillator Amplitude
V
(OSC)
(peak to peak)
1.6
V
Error Amplifier Section
Input Bias Current
I
BIAS
V
FB
=3V
-0.1
-2
A
Input Voltage
V
I(E.A)
V
pin1
= 2.5V
2.42
2.5
2.58
V
Open Loop Voltage Gain
A
VOL
2V
V
0
4V
65
90
dB
Unity Gain Bandwidth
UGBW
T
j
=25
0
C, Note 3
0.5
0.6
MHz
Power Supply Rejection Ratio
PSRR
12V V
CC
25 V
60
70
dB
Output Sink Current
I
SINK
V
pin2
= 2.7V, V
pin1
= 1.1V
2
7
mA
Output Source Current
I
SOURCE
V
pin2
= 2.3V, V
pin1
= 5V
-0.5
-1.0
mA
High Output Voltage
V
OH
V
pin2
= 2.3V, R
L
= 15K
to GND
5.0 6.0
Low Output Voltage
V
OL
V
pin2
= 2.7V, R
L
= 15K
to PIN 8
0.8
1.1
V
Current Sense Section
Gain G
V
(Note 1 & 2)
2.85
3.0
3.15
V/V
Maximum Input Signal
V
I(MAX)
V
pin1
= 5V (Note1)
0.9
1.0
1.1
V
Supply Voltage Rejection
SVR
12V V
CC
25 V (Note 1)
70
dB
Input Bias Current
I
BIAS
V
pin3
= 3V
-3.0
-10
A
Output Section
I
SINK
= 20 mA
0.08
0.4
Low Output Voltage
V
OL
I
SINK
= 200 mA
1.4
2.2
I
SINK
= 20 mA
13
13.5
High Output Voltage
V
OH
I
SINK
= 200 mA
12
13.0
V
Rise Time
t
R
T
J
= 25
C, C
L
= 1nF (Note 3)
45
150
Fall Time
t
F
T
J
= 25
C, C
L
= 1nF (Note 3)
35
150
nS
Undervoltage Lockout Section
MIK3842A-BW/44A-BW
14.5 16.0 17.5
Start Theshold
V
TH(ST)
MIK3843A-BW/45A-BW
7.8 8.4 9.0
V
MIK3842A-BW/44A-BW 8.5
10
11.5
Min. Operating Voltage
(After Turn On)
V
OPR(min)
MIK3843A-BW/45A-BW
7.0 7.6 8.2
V
PWM Section
MIK3842A-BW/43A-BW 95
97
100
Max. Duty Cycle
D
(MAX)
MIK3844A-BW/45A-BW
47 48 50
Min. Duty Cycle
D
(MAX)
0
%
Total Standby Current
Start
-Up Current
I
ST
MIK384XA-BW
0.17 0.3
Operating Supply Current
I
CC (OPR)
V
pin3
= V
pin2
= 0V
13
17
mA
Zener Voltage
V
Z
I
CC
=25 mA
30
38
V
* 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.
Page 2 of 8
Replacement of
UC3842A/43A/44A/45A-BW
MIK3842A/43A/44A/45A-BW
High Performance Current
Mode PWM Controller
July 2002
Pin functions
N Function
Description
1
COMP
This pin is the Error Amplifier output and is made for loop compensation.
2 V
FB
This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply
output through a resistor divider.
3 I
SENSE
A voltage proportional to inductor current is connected to this input. The PWM uses this information to
terminate the output switch conduction.
4 R
T
/C
T
The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor R
T
to V
ref
and capacitor C
T
to ground.
5
GROUND
This pin is the combined control circuitry and power ground.
6
OUTPUT
This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sink by
this pin.
7 V
CC
This pin is the positive supply of the integrated circuit.
8 V
ref
This is the reference output. It provides charging current for capacitor C
T
through resistor R
T
.
Application information
+
_
2.5V
2
1
1mA
V
FB
COMP
Figure 1. Error Amp Configuration
7
V
ON
MIK3842
MIK3844
MIK3843
MIK3845
V
OFF
16V
10V
8.4V
7.6V
ON/OFF COMMAND TO S/R OF IC
V
CC
I
CC
V
CC
V
OFF
V
ON
13mA
0.2mA
During UVLO, the Output is low
Figure 2. Undervoltage Lockout
ERROR
AMP
2R
2
1
3
5
+
_
R
1V
CURRENT
SENSE
COMPARATOR
R
R
S
C
CURRENT
SENSE
GND
COMP
V
FB
I
S
Peak current is determined by I
S max
1.0V
R
S
Figure 3. Current Sense Circuit
Page 3 of 8
Replacement of
UC3842A/43A/44A/45A-BW
MIK3842A/43A/44A/45A-BW
High Performance Current
Mode PWM Controller
July 2002
R
1
R
T
R
T
R
SLOPE
R
SLOPE
R
S
R
1
R
S
R
T
/C
T
R
T
/C
T
I
SENSE
I
SENSE
GND
GND
MIK3842
MIK3842
I
S
I
S
V
REF
V
REF
8
4
3
5
8
4
3
5
Figure 4. Slope Compensation Techniques
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
2R
R
R
I
R
d
C
f
R
f
COMP
EA
From V
0
V
FB
+
-
+
1mA
2.5 V
2
1
5
2R
R
R
p
R
I
R
d
C
f
C
p
R
f
EA
COMP
From V
0
V
FB
+
-
+
2.5 V
2
1
5
1mA
Error Amp compensation circuit for stabilizing any current-mode topology except
for boost and flyback converters operating with continuous inductor current.
Error Amp compensation circuit for stabilizing current-mode boost and flyback
topologies operating with continuous inductor current.
Figure 6. Error Amplifier Compensation
Page 4 of 8
Replacement of
UC3842A/43A/44A/45A-BW
MIK3842A/43A/44A/45A-BW
High Performance Current
Mode PWM Controller
July 2002
Figure 7. External Clock Synchronization
Figure 8. Soft-Start Circuit
Page 5 of 8
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