KA3844 [ESTEK]
fixed frequency current mode PWM controller; 固定频率电流模式PWM控制器
| 型号： | KA3844 |
| 厂家： | 
Estek Electronics Co. Ltd |
| 描述： | fixed frequency current mode PWM controller |
| 文件： | 总7页 (文件大小：321K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Description
The 3842A(AM)/43A(AM)/44A(AM)/45A(AM) 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 3842A(AM) and 3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding
thresholds for the 3843A(AM)/45A(AM) are 8.4V (on) and 7.6V (off). The MIK3842A(AM) and MIK3843A(AM) can operate within 100% duty
cycle. The 3844A(AM) and UC3845A(AM) can operate within 50% duty cycle.
The 384XA(AM) has Start-Up Current 0.17mA (typ).
Features
Pin Connection
•
•
•
•
Low Start-Up and Operating Current
High Current Totem Pole Output
Undervoltage Lockout With Hysteresis
Operating Frequency Up To 300KHz (384XA)
500KHz (384XAM
)
Top view
Block diagram
(toggle flip flop used only in MIK3844, MIK3845)
36V
GND
5V
V
SET
/
E
RE
S
T
REF
UVLO
V
GOOD
F
RE
LOGI
C
IN
T
E
RNAL
BIAS
POWER
V
CC
OU
7
1/2 V
REF
2R
+
V
ER
R
C.
CO
S
M
.
FB
2
P
1V
T
R
PW
M
COM
P
LA CH
T
CUR
RENT
SEN
S
E
3
5
R
/C
T
OSCILLATOR
Absolute Maximum Ratings
Symbol
Parameter
Maximum
Units
VCC
IO
Supply Voltage (low impedance source)
30
±1
V
A
Output Current
VI
ISINK (E.A)
Po
Input Voltage (Analog Inputs pins 2,3)
Error Amp Output Sink Current
Power Dissipation (TA=250C)
Storage Temperature Range
−
0.3 to 5.5
V
mA
W
10
1
Tstg
-65 to150
260
oC
o
TL
Lead Temperature (soldering 5 sec.)
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1
Electrical characteristics
(*VCC=15V, RT=10kΩ, CT=3.3nF, TA=00C to +700C, unless otherwise specified)
Characteristics
Symbol
Test Conditions
Min
Typ
Max
Units
Reference Section
Reference Output Voltage
Line Regulation
V
REF
TJ = 25°C, IREF = 1 mA
4.9
5.0
6.0
5.1
20
V
mV
∆VREF
∆VREF
12V ≤ VCC ≤ 25 V
1 mA ≤ IREF ≤ 20mA
TA = 25°C
Load Regulation
6.0
25
Short Circuit Output Current
Oscillator Section
ISC
-100
-180
mA
MIK384XA
MIK384XAM
47
47
50
52
57
57
f
TJ = 25°C
Oscillation Frequency
KHz
Frequency Change with Voltage
Oscillator Amplitude
Error Amplifier Section
Input Bias Current
∆f/∆VCC
12V ≤ VCC ≤ 25 V
0.05
1.6
1.0
%
V
V(OSC)
(peak to peak)
IBIAS
VI(E.A)
AVOL
VFB=3V
-0.1
2.5
90
-2
µA
V
Input Voltage
Vpin1 = 2.5V
2.42
65
2.58
Open Loop Voltage Gain
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
Current Sense Section
Gain
2V ≤ V0 ≤ 4V
dB
PSRR
ISINK
12V ≤ VCC ≤ 25 V
Vpin2 = 2.7V, Vpin1 = 1.1V
Vpin2 = 2.3V, Vpin1 = 5V
Vpin2 = 2.3V, RL = 15KΩ to GND
Vpin2 = 2.7V, RL = 15KΩ to PIN 8
60
70
2
7
mA
mA
ISOURCE
-0.5
5.0
-1.0
6.0
0.8
V
V
OH
V
OL
1.1
GV
(Note 1 & 2)
2.85
0.9
3.0
1.0
70
3.15
1.1
V/V
V
Maximum Input Signal
Supply Voltage Rejection
Input Bias Current
VI(MAX)
SVR
IBIAS
V pin1 = 5V (Note1)
12V ≤ VCC ≤ 25 V (Note 1)
Vpin3 = 3V
dB
µA
-3.0
-10
Output Section
Low Output Voltage
VOL
VOH
ISINK = 20 mA
0.08
1.4
0.4
2.2
ISINK = 200 mA
V
High Output Voltage
ISINK = 20 mA
13
12
13.5
13.0
45
ISINK = 200 mA
Rise Time
tR
F
TJ = 25°C, CL = 1nF (Note 3)
TJ = 25°C, CL = 1nF (Note 3)
150
150
nS
Fall Time
t
35
Undervoltage Lockout Section
Start Theshold
MIK3842A(AM)/44A(AM)
MIK3843A(AM)/45A(AM)
MIK3842A(AM)/44A(AM)
MIK3843A(AM)/45A(AM)
14.5
7.8
16.0
8.4
10
17.5
9.0
VTH(ST)
V
V
VOPR(min)
Min. Operating Voltage
(After Turn On)
8.5
11.5
8.2
7.0
7.6
PWM Section
MIK3842A(AM)/43A(AM)
MIK3844A(AM)/45A(AM)
95
47
97
48
100
50
0
Max. Duty Cycle
D(MAX)
D(MAX)
%
Min. Duty Cycle
Total Standby Current
Start
−
Up Current
IST
ICC (OPR)
VZ
MIK384XA(AM)
Vpin3 = Vpin2 = 0V
ICC=25 mA
0.17
13
0.3
17
mA
V
Operating Supply Current
Zener Voltage
30
38
* - Adjust VCC above the start threshold before setting it to 15V.
Note 1: Parameter measured at trip point of latch with Vpin2=0.
Note 2: Gain defined as A=∆Vpin1/∆Vpin3 ; 0 ≤ Vpin3 ≤ 0.8V.
Note 3: These parameters, although guaranteed, are not 100% tested in production.
BEIJING ESTEK ELECTRONICS CO.,LTD
2
Pin functions
N
1
2
Function
COMP
VFB
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.
3
4
ISENSE
RT/CT
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 RT to Vref
and capacitor CT to ground.
5
6
GROUND
OUTPUT
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.
7
8
VCC
Vref
This pin is the positive supply of the integrated circuit.
This is the reference output. It provides charging current for capacitor CT through resistor RT .
Application information
2.5V
1mA
VFB
2
1
COMP
Figure 1. Error Amp Configuration
VCC
7
ON/OFF COMMAND TO S/R OF IC
ICC
MIK3842 MIK3843
MIK3844 MIK3845
13mA
8.4V
7.6V
16V
10V
VON
0.2mA
VOFF
VCC
VOFF VON
During UVLO, the Output is low
Figure 2. Undervoltage Lockout
ERROR
+
AMP
2R
2
_
VFB
1V
CURRENT
SENSE
COMPARATOR
COMP
1
5
R
IS
R
CURRENT
SENSE
RS
C
GND
1.0V
RS
Peak current is determined by IS max
Figure 3. Current Sense Circuit
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3
VREF
RT /CT
ISENSE
VREF
8
4
8
RT
RT
RT /CT
4
RSLOPE
IS
MIK3842
RSLOPE
MIK3842
IS
R1
R1
ISENSE
3
3
5
5
RS
RS
GND
GND
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
From V0
From V0
RI
+
+
1mA
2.5 V
2.5 V
+
Rp
1mA
2R
2R
+
RI
VFB
VFB
f
-
-
EA
2
EA
2
Cp
Cf
Rd
Rf
Cf
R
R
1
1
COMP
COMP
5
5
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
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4
Figure 7. External Clock Synchronization
Figure 8. Soft-Start Circuit
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5
Typical Performance Characteristics
R
(K
T
%
50
50
2nF
C
1nF
C
30
5nF
5nF
C
C
500pF
20
10
C
20
10
10nF
C
200pF
C
5
5
100pF
C
10nF
C
3
2
V
= 15 V
O
CC
2
1
V
=
15
CC
2O 5
T
=
25
T
1
10
10
20
30
50
100
200
300
20
30
50
100
200
300
KHz)
KHz)
f
Figure 1. Timing Resistor vs. Oscillator Frequency.
f
Figure 2. Output Dead-Time vs. Oscillator Frequenc .y
Dmax
(%)
(dB)
V
=
15 V
CC
=
90
80
V
2V to 4V
O
100K
O
25
R
=
L
C
80
70
60
40
60
50
40
20
15 V
V
3.3nF
=
CC
T
=
25
0
-20
3
5
1
2
10
100
1K
10K
100K
1M
f (Hz)
R (
T
Figure 3. Maximum Output Duty Cycle vs.
Timing Resistor (MIK3842/4 .3)
Figure 4. Error Amp Open-Loop Gain vs.
Fr equency
.
V
th
I
SC
(mA)
(V)
V
= 15 V
V
= 15V
CC
100
1.0
90
80
0.8
0.6
O
25 C
T
O
125 C
T
70
0.4
0.2
60
50
O
)
0
25 50
75
100
T
0
2
4
V
(
O
Figure 6. Reference Short Circuit Current vs.
Temperature
Figure 5. Current Sense Input Threshold vs.
Error Amp Output Voltage.
.
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6
V
I
sat
(V)
CC
(mA)
Sourse Saturation
(Load to Ground)
-1
15 V
V
20
-2
80
µ
Pulsed Load 120Hz
15
3
2
10
I
0V
=
Sense
10K
R
Sink Saturation
(Load to
T
=
25
1
5
0
A
3.3nF
C
0
0
200
400
600
0
10 20
30
I
(
m
V
(
CC
O
Figure
.7 Output Saturation Voltage vs. Load
T
Figure .8 Supply Current vs. Supply
VCC
7
Vref
8
R /CT
T
5V REG
OUTPUT
LARGE
PWM
CLOCK
6
R
/ SMALL C
T
OUTPUT
RT
4
OSCILLATOR
R
C
T
R /C
T
T
/
T
ID
OUTPUT
SMALL RT / LARGE
5
GND
Figure 9. Oscillator and Output Waveforms
Ordering Information
ORDERI N
G
NUM BER
PACKA
G
E
M AR K ING
-
-
SOP 8 / DIP 8
KA3842/ 43 / 44/45
3842/ 43 / 44/45
Address :
6A06--6A07
Rm 6A07,Changyin Office Building ,No.88,Yong Ding Road,Hai Dian District ,Beijing
Postalcode:100039
Tel: 86-010-58895780 / 81 / 82 / 83 / 84
Http://www.estek.com.cn
Fax : 010-58895793
Email:sales@estek.com.cn
REV No:01-060815
BEIJING ESTEK ELECTRONICS CO.,LTD
7
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