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PDF UC3844D Data sheet ( Hoja de datos )
| Número de pieza | UC3844D | |
| Descripción | HIGH PERFORMANCE CURRENT MODE CONTROLLERS | |
| Fabricantes | Motorola Semiconductors | |
| Logotipo |  |
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Order this document by UC3844/D
High Performance
Current Mode Controllers
The UC3844, UC3845 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
an oscillator, 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,
a latch for single pulse metering, and a flip–flop which blanks the output off
every other oscillator cycle, allowing output deadtimes to be programmed for
50% to 70%.
These devices are available in an 8–pin dual–in–line 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 UCX844 has UVLO thresholds of 16 V (on) and 10 V (off), ideally
suited for off–line converters. The UCX845 is tailored for lower voltage
applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).
• Current Mode Operation to 500 kHz Output Switching Frequency
• Output Deadtime Adjustable from 50% to 70%
• Automatic Feed Forward Compensation
• Latching PWM for Cycle–By–Cycle Current Limiting
• Internally Trimmed Reference with Undervoltage Lockout
• High Current Totem Pole Output
• Input Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
• Direct Interface with Motorola SENSEFET Products
Vref
8(14)
RTCT
4(7)
Voltage
Feedback
2(3)
1(1)
Output
Comp.
Simplified Block Diagram
VCC 7(12)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
–
Error
Amplifier
Flip
Flop
&
Latching
PWM
VC
7(11)
Output
6(10)
PWR GND
5(8)
Current
Sense
3(5)
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO–14 package.
UC3844, 45
UC2844, 45
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
8
1
14
1
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
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
RT/CT 7
8 Power Ground
(Top View)
ORDERING INFORMATION
Device
Operating
Temperature Range
Package
UC3844D
SO–14
UC3845D
UC3844N
TA = 0° to +70°C
SO–14
Plastic
UC3845N
Plastic
UC2844D
SO–14
UC2845D
UC2844N
TA = – 25° to +85°C
SO–14
Plastic
UC2845N
Plastic
MOTOROLA ANALOG IC DEVICE DATA
© Motorola, Inc. 1996
Rev 1
1
1 page  
UC3844, 45 UC2844, 45
0
–4.0
–8.0
–12
–16
–20
–24
0
Figure 7. Reference Voltage Change
versus Source Current
VCC = 15 V
TA = 125°C
TA = –55°C
TA = 25°C
20 40 60 80 100
Iref, REFERENCE SOURCE CURRENT (mA)
120
Figure 8. Reference Short Circuit Current
versus Temperature
110
VCC = 15 V
RL ≤ 0.1 Ω
90
70
50
–55 –25 0 25 50 75 100 125
TA, AMBIENT TEMPERATURE (°C)
Figure 9. Reference Load Regulation
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
Figure 10. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
2.0 ms/DIV
2.0 ms/DIV
Figure 11. Output Saturation Voltage
versus Load Current
0
VCC
Source Saturation
(Load to Ground)
VCC = 15 V
80 µs Pulsed Load
–1.0 TA = 25°C
120 Hz Rate
–2.0
TA = –55°C
3.0
2.0
1.0
0
0
TA = –55°C
TA = 25°C
Sink Saturation
(Load to VCC)
Gnd
200 400 600
IO, OUTPUT LOAD CURRENT (mA)
800
90%
10%
Figure 12. Output Waveform
VCC = 15 V
CL = 1.0 nF
TA = 25°C
50 ns/DIV
MOTOROLA ANALOG IC DEVICE DATA
5
5 Page 
UC3844, 45 UC2844, 45
Figure 24. MOSFET Parasitic Oscillations
VCC
7(12)
Vin
5.0Vref
+
+–
–
+
–+
–
T
S
–+ R Q
Comp/Latch
7(11)
Rg
6(10)
5(8)
Q1
3(5)
RS
Series gate resistor Rg will damp any high frequency parasitic oscillations
caused by the MOSFET input capacitance and any series wiring inductance
in the gate–source circuit.
Figure 25. Bipolar Transistor Drive
IB Vin
+
0
Base Charge
Removal
–
C1
Q1
6(1)
5(8)
3(5)
RS
The totem–pole output can furnish negative base current for enhanced
transistor turn–off, with the addition of capacitor C1.
Figure 26. Isolated MOSFET Drive
VCC
7(12)
Vin
5.0Vref
+– +
+ +–
–
–
T
S
–+ RQ
Comp/Latch
Isolation
Boundary
7(11)
6(10)
5(8)
R
ÉÉÉ ÉÉÉÉVGSWaveforms
Q1
+
0
–
50% DC
+
0
–
25% DC
Ipk =
V(pin 1) – 1.4
3 RS
NP
NS
3(5) C
RS NS
Np
Figure 27. Latched Shutdown
MCR 2N
101 3905
8(14)
4(7)
2(3)
1(1)
2N
3903
R
Bias
R
Osc
+
+–
EA
1.0mA
2R
R
5(9)
The MCR101 SCR must be selected for a holding of less than 0.5 mA at
TA(min). The simple two transistor circuit can be used in place of the SCR as
shown. All resistors are 10 k.
Figure 28. Error Amplifier Compensation
From VO
Ri
Rd CI
Rf ≥ 8.8 k
2.5V +
2(3) + 1.0mA
–
Rf
EA 2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing any current–mode topology except
for boost and flyback converters operating with continuous inductor current.
From VO
Rp Ri
Cp Rd CI
2.5V +
2(3) + 1.0mA
Rf
–
EA
2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing current–mode boost and flyback
topologies operating with continuous inductor current.
MOTOROLA ANALOG IC DEVICE DATA
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet UC3844D.PDF ] | |
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