KA3842B.pdf

(91 KB) Pobierz
KA3842B/KA3843B/KA3844B/KA3845B SMPS Controller
www.fairchildsemi.com
KA3842B/KA3843B/KA3844B/KA3845B
SMPS Controller
Features
• Low Start Up Current
• Maximum Duty Clamp
• UVLO With Hysteresis
• Operating Frequency Up To 500KHz
Description
The KA3842B/KA3843B/KA3844B/KA3845B are fixed
frequency current-mode PWM controller. They are spe-
cially designed for Off - Line and DC-to-DC converter
applications with minimum external components. These
integrated circuits feature 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 circuity Includes built in
under-voltage lockout and current limiting. The KA3842B
and KA3844B have UVLO thresholds of 16V (on) and
10V (off) The KA3843B and KA3845B are 8.5V (on) and
7.9V (off) The KA3842B and KA3843B can operate within
100% duty cycle. The KA3844B and KA3845B can operate
with 50% duty cycle.
8-DIP
1
14-SOP
1
Rev. 5.0
©2000 Fairchild Semiconductor International
214298705.006.png 214298705.007.png 214298705.008.png 214298705.009.png
KA3842B/KA3843B/KA3844B/KA3845B
Internal Block Diagram
Absolute Maximum Ratings
Parameter
Symbol
Value
Unit
Supply Voltage
V CC
30
V
Output Current
IO
1
A
Analog Inputs (Pin 2.3)
V (ANA)
-0.3 to 6.3
V
Error Amp Output Sink Current
I SINK (E.A)
10
mA
Power Dissipation (T A = 25
C)
P D
1
W
2
214298705.001.png
KA3842B/KA3843B/KA3844B/KA3845B
Electrical Characteristics
(V CC =15V, R T =10K
, C T =3.3nF, T A = 0
C to +70
C, unless otherwise specified)
Parameter
Symbol
Conditions
Min.
Typ. Max. Unit
REFERENCE SECTION
Reference Output Voltage
V REF
T J = 25
C, I REF = 1mA
4.90
5.00 5.10
V
Line Regulation
V REF
12V
V CC
25V
-
6
20
mV
Load Regulation
V REF
1mA
I REF
20mA
-
6
25
mV
Short Circuit Output Current
ISC
TA = 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
25V
-
0.05
1
%
Oscillator Amplitude
V OSC
-
-
1.6
-
V P-P
ERROR AMPLIFIER SECTION
Input Bias Current
I BIAS
-
-
-0.1
-2
A
Input Voltage
V I(E>A)
V 1 = 2.5V
2.42
2.50 2.58
V
Open Loop Voltage Gain
G VO
2V
V O
4V
65
90
-
dB
Power Supply Rejection Ratio
PSRR
12V
V CC
25V
60
70
-
dB
Output Sink Current
I SINK
V 2 = 2.7V, V 1 = 1.1V
2
7
-
mA
Output Source Current
I SOURCE V 2 = 2.3V, V 1 = 5V
-0.6
-1.0
-
mA
High Output Voltage
V OH
V 2 = 2.3V, R L = 15K
to GND
5
6
-
V
Low Output Voltage
V OL
V 2 = 2.7V, R L = 15K
to Pin 8
-
0.8
1.1
V
CURRENT SENSE SECTION
Gain
GV
(Note 1 & 2)
2.85
3
3.15
V/V
Maximum Input Signal
V I(MAX)
V 1 = 5V(Note 1)
0.9
1
1.1
V
Power Supply Rejection Ratio
PSRR
12V
V CC
25V (Note 1)
-
70
-
dB
Input Bias Current
I BIAS
-
-
-3
-10
A
OUTPUT SECTION
Low Output Voltage
VOL
ISINK = 20mA
-
0.08
0.4
V
I SINK = 200mA
-
1.4
2.2
V
High Output Voltage
VOH
I SOURCE = 20mA
13
13.5
-
V
I SOURCE = 200mA
12
13.0
-
V
Rise Time
t R
T J = 25
C, C L = 1nF (Note 3)
-
45
150
ns
Fall Time
t F
T J = 25
C, C L = 1nF (Note 3)
-
35
150
ns
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold
VTH(ST)
KA3842B/KA3844B
14.5
16.0 17.5
V
KA3843B/KA3845B
7.8
8.4
9.0
V
Min. Operating Voltage
(After Turn On)
V OPR(MIN)
KA3842B/KA3844B
8.5
10.0
11.5
V
KA3843B/KA3845B
7.0
7.6
8.2
V
3
214298705.002.png 214298705.003.png
KA3842B/KA3843B/KA3844B/KA3845B
Electrical Characteristics (Continued)
(V CC =15V, R T =10K
, C T =3.3nF, T A = 0
C to +70
C unless otherwise specified)
Parameter
Symbol
Conditions
Min.
Typ. Max. Unit
PWM SECTION
Max. Duty Cycle
D (max)
KA3842B/KA3843B
95
97
100
%
D
KA3844B/KA3845B
47
48
50
%
Min. Duty Cycle
D (MIN)
-
-
-
0
%
TOTAL STANDBY CURRENT
Start-Up Current
I ST
-
-
0.45
1
A
Operating Supply Current
I CC(OPR) V 3 =V 2 =ON
-
14
17
mA
Zener Voltage
V Z
I CC = 25mA
30
38
-
V
Adjust V CC above the start threshould before setting at 15V
Note:
1. Parameter measured at trip point of latch
2. Gain defined as:
A
=
V 1
,0
V3
0.8V
V 3
3.These parameters, although guaranteed, are not 100 tested in production.
Figure 1. Open Loop Test Circuit
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.
4
----------
214298705.004.png
KA3842B/KA3843B/KA3844B/KA3845B
Figure 2. Under Voltage Lockout
During Under-Voltage 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.
Figure 3. Error Amp Configuration
Figure 4. Current Sense Circuit
Peak current (I S ) is determined by the formula:
I S
MAX
=
1.0V
R S
A small RC filter may be required to suppress switch transients.
5
------------
214298705.005.png

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin