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UC3844B 데이터시트 PDF




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부품번호 UC3844B 기능
기능 UC3842B/3B/4B/5B - High Performance Current Mode Controllers
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UC3844B 데이터시트, 핀배열, 회로
High Performance Current Mode Controllers
General Description
UC3842B/3B/4B/5B,UC2842B/3B
Package outline
The UC3842B/3B/4B/5B, series are high performance fixed
frequency current mode controllers. They are specifically designed for
Off–Line and dc–to–dc converter applications offering the designer a
cost–effective solution with minimal 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 totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle–by–cycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8–pin dual–in–line and surface
mount (SO–8) plastic package as well as the 14–pin plastic surface
mount (SO–14). The SO–14 package has separate power and ground
pins for the totem pole output stage.
The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off–line converters. The UCX843B is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
Trimmed Oscillator for Precise Frequency Control
Oscillator Frequency Guaranteed at 250 kHz
Current Mode Operation to 500 kHz
Automatic Feed Forward Compensation
Latching PWM for Cycle–By–Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Vref
8(14)
RT/CT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
VCC 7(12)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
-
Error
Amplifier
Latching
PWM
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO-14 package.
Figure 1. Simplified Block Diagram
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
8
1
8
1
DIP-8
SOP-8
14
1
SOP-14
Pin Connections
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
8 Vref
7 VCC
6 Output
5 Gnd
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC 4
Current Sense 5
NC 6
RT/CT 7
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
8 Power Ground
(Top View)
@ 2010 Copyright By American First Semiconductor
Page 1/16




UC3844B pdf, 반도체, 판매, 대치품
UC3842B/3B/4B/5B,UC2842B/3B
Electrical Characteristics (VCC = 15 V [Note 8], RT = 10 k, CT = 3.3 nF, for typical values TA = 25°C, for min/max values
TA is the operating ambient temperature range that applies [Note 9], unless otherwise noted.)
UC284XB
UC384XB, BV
Characteristics
Symbol
Min Typ Max Min
Typ Max
Pwm Section
Duty Cycle
MMaaxxiimmuumm (UC284XB, UC384XB)
Minimum
Total Device
Power Supply Current
Startup (VCC = 6.5 V for UCX843B,
Startup (VCC 14 V for UCX842B)
Operating (Note 8)
DC(max)
DC(min)
ICC + IC
94 96
––
0
– 0.17 0.3
– 13 17
94 96
––
0
– 0.17 0.3
– 13 17
Power Supply Zener Voltage (ICC = 25 mA)
VZ 30 36 – 30 36
8. Adjust VCC above the Startup threshold before setting to 15 V.
9. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
Tlow = 0°C for UC3842B/3B/4B/5B; –25°C for UC2842B/3B
Thigh = +70°C for UC3842B/3B/4B/5B; +85 °C for UC2842B/3B
Unit
%
mA
V
80
50
20
8.0
5.0
2.0 VCC = 15 V
TA = 25°C
0.8
10 k
20 k
50 k 100 k 200 k
500 k
fOSC, OSCILLATOR FREQUENCY (kHz)
Figure 2. Timing Resistor
versus Oscillator Frequency
1.0 M
9.0
VCC = 15 V
VOSC = 2.0 V
8.5
8.0
7.5
7.0
-Ă55
-Ă25 0
25 50 75
TA, AMBIENT TEMPERATURE (°C)
100
Figure 4. Oscillator Discharge Current
versus Temperature
125
100
1. CT = 10 nF
50 2. CT = 5.0 nF
3. CT = 2.0 nF
4. CT = 1.0 nF
20 5. CT = 500 pF
6. CT = 200 pF
10 7. CT = 100 pF
5.0
4
3
2
1
7
6
5
2.0
1.0
10 k
VCC = 15 V
TA = 25°C
20 k
50 k 100 k 200 k
500 k
fOSC, OSCILLATOR FREQUENCY (kHz)
Figure 3. Output Deadtime
versus Oscillator Frequency
1.0 M
100
90
80 Idischg = 7.5 mA
70
60
Idischg = 8.8 mA
VCC = 15 V
CT = 3.3 nF
50 TA = 25°C
40
0.8 1.0
2.0 3.0 4.0 5.0 6.0 7.0 8.0
RT, TIMING RESISTOR (k)
Figure 5. Maximum Output Duty Cycle
versus Timing Resistor
www.First-semi.com
Page 4/16

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UC3844B 전자부품, 판매, 대치품
UC3842B/3B/4B/5B,UC2842B/3B
Pin
8–Pin 14–Pin
11
23
35
47
5
6 10
7 12
8 14
8
11
9
2,4,6,13
Function
Compensation
Voltage
Feedback
Current
Sense
RT/CT
Gnd
Output
VCC
Vref
Power
Ground
VC
Gnd
NC
Pin Function Description
Description
This pin is the Error Amplifier output and is made available 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. Operation to 500 kHz
is possible.
This pin is the combined control circuitry and power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are
sourced and sunk by this pin.
This pin is the positive supply of the control IC.
This is the reference output. It provides charging current for capacitor CT through resistor RT.
This pin is a separate power ground return that is connected back to the power source. It is
used to reduce the effects of switching transient noise on the control circuitry.
The Output high state (VOH) is set by the voltage applied to this pin. With a separate
power source connection, it can reduce the effects of switching transient noise on the
control circuitry.
This pin is the control circuitry ground return and is connected back to the power
source ground.
No connection. These pins are not internally connected.
www.First-semi.com
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