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UC3842A の電気的特性と機能

UC3842AのメーカーはETCです、この部品の機能は「High Performance Current Mode PWM Controller」です。


製品の詳細 ( Datasheet PDF )

部品番号 UC3842A
部品説明 High Performance Current Mode PWM Controller
メーカ ETC
ロゴ ETC ロゴ 




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UC3842A Datasheet, UC3842A PDF,ピン配置, 機能
Replacement of
UC3842A/43A/44A/45A
High Performance Current
Mode PWM Controller
MIK3842A/43A/44A/45A
July 1995 –revised July 2002
Description
The MIK3842A(AM)/43A(AM)/44A(AM)/45A(AM) are fixed frequency current mode PWM controller. They are specially designed for
OFFLine 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(AM) and MIK3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding
thresholds for the MIK3843A(AM)/45A(AM) are 8.4V (on) and 7.6V (off). The MIK3842A(AM) and MIK3843A(AM) can operate within 100%
duty cycle. The MIK3844A(AM) and UC3845A(AM) can operate within 50% duty cycle.
The MIK384XA(AM) has Start-Up Current 0.17mA (typ).
Features
Low Start-Up and Operating Current
High Current Totem Pole Output
Undervoltage Lockout With Hysteresis
Operating Frequency Up To 300KHz (MIK384XA)
500KHz (MIK384XAM)
Pin Connection
VREF
8
Block diagram
(toggle flip flop used only in MIK3844, MIK3845)
5V
VREF
SET/
RESET
UVLO
Top view
VCC 7
36V GND
5
INTERNAL
BIAS
VREF GOOD
LOGIC
2 VFB
1/2 VREF
+ ERR
- AMP
COMP
1
CURRENT
SENSE
3
2R
R
C.S.
COMP
1V
4 RT/CT
OSCILLATOR
R
PWM
LATCH
S
T
POWER VCC
7
OUT
6
5
POWER GND
Absolute Maximum Ratings
Symbol
Parameter
VCC
IO
VI
ISINK (E.A)
PO
Tstg
TL
Supply Voltage (low impedance source)
Output Current
Input Voltage (Analog Inputs pins 2,3)
Error Amp Output Sink Current
Power Dissipation (TA=250C)
Storage Temperature Range
Lead Temperature (soldering 5 sec.)
Maximum
30
±1
0.3 to 5.5
10
1
-65 to150
260
Units
V
A
V
mA
W
oC
oC
Page 1 of 8

1 Page





UC3842A pdf, ピン配列
Replacement of
UC3842A/43A/44A/45A
MIK3842A/43A/44A/45A
High Performance Current
Mode PWM Controller
July 1995 –revised July 2002
Pin functions
N Function
1 COMP
2 VFB
3 ISENSE
4 RT/CT
5 GROUND
6 OUTPUT
7 VCC
8 Vref
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 RT to Vref
and capacitor CT 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 CT through resistor RT .
Application information
2.5V
1mA
VFB 2
COMP 1
Figure 1. Error Amp Configuration
VCC 7
ON/OFF COMMAND TO S/R OF IC
ICC
MIK3842 MIK3843
MIK3844 MIK3845
VON 16V 8.4V
VOFF 10V 7.6V
13mA
0.2mA
VCC
V VOFF
ON
During UVLO, the Output is low
Figure 2. Undervoltage Lockout
+
VFB 2 _
COMP 1
ERROR
AMP
IS
2R
1V
R
CURRENT
SENSE
COMPARATOR
R3
CURRENT
RS
C SENSE
5
GND
Peak current is determined by IS max
1.0V
RS
Figure 3. Current Sense Circuit
Page 3 of 8


3Pages


UC3842A 電子部品, 半導体
Replacement of
UC3842A/43A/44A/45A
High Performance Current
Mode PWM Controller
MIK3842A/43A/44A/45A
July 1995 –revised July 2002
RT
(K)
50
CT= 5nF
20
Typical Performance Characteristics
CT
CT =
C
= 200pF
500pF
CT = 100pF
CT
=
T
2nF
=
1nF
%
50
CT= 1nF
30
20 CT= 500pF
CT= 2nF
CT= 5nF
CT= 10nF
10
5
CT= 10nF
Dm ax
(%)
2 VCC = 15 V
TA = 25 OC
1
10 20 30
50
100
200 300 500
fOSC (KHz)
Figure 1. Timing Resistor vs. Oscillator Frequency.
10
CT= 200pF
5
3
2
CT= 100pF
VCC = 15 V
TA = 25 OC
1
10 20 30 50
100
200 300 500
fOSC (KHz)
Figure 2. Output Dead-Time vs. Oscillator Frequency.
(d B)
90
80
VCC = 15 V
VO = 2V to 4V
RL= 100K
TA = 25 OC
80 60
70 40
60
VCC = 15 V
CT= 3.3nF
50 TA = 25 OC
40
1
Figure
3.
2
Maximum
3
Output
Duty
5
Cycle
vsR. T(K)
Timing Resistor (MIK3842/43).
Vth
(V)
1.0 VCC = 15V
20
0
-20
10
ISC
(mA)
100
100 1K 10K 100K 1M f (Hz)
Figure 4. Error Amp Open-Loop Gain vs.
Frequency.
VCC = 15 V
0.8
TA = 25OC
0.6
TA = 125OC
0.4
90
80
70
0.2
02
4
6 VO (V)
Figure 5. Current Sense Input Threshold vs.
Error Amp Output Voltage.
60
50
0 25 50 75 100 TA (OC)
Figure 6. Reference Short Circuit Current vs.
Temperature.
Page 6 of 8

6 Page



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