UC2844J [ETC]
Current-Mode SMPS Controller ; 电流模式开关电源控制器\n型号: | UC2844J |
厂家: | ETC |
描述: | Current-Mode SMPS Controller
|
文件: | 总8页 (文件大小:463K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
Current Mode PWM Controller
FEATURES
DESCRIPTION
•
Optimized For Off-line And DC
To DC Converters
The UC1842/3/4/5 family of control ICs provides the necessary features to im-
plement off-line or DC to DC fixed frequency current mode control schemes
with a minimal external parts count. Internally implemented circuits include un-
der-voltage lockout featuring start up current less than 1mA, a precision refer-
ence trimmed for accuracy at the error amp input, logic to insure latched
operation, a PWM comparator which also provides current limit control, and a
totem pole output stage designed to source or sink high peak current. The out-
put stage, suitable for driving N Channel MOSFETs, is low in the off state.
•
•
Low Start Up Current (<1mA)
Automatic Feed Forward
Compensation
•
•
Pulse-by-pulse Current Limiting
Enhanced Load Response
Characteristics
Differences between members of this family are the under-voltage lockout
thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have
UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applica-
tions. The corresponding thresholds for the UC1843 and UC1845 are 8.4V
and 7.6V. The UC1842 and UC1843 can operate to duty cycles approaching
100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the
addition of an internal toggle flip flop which blanks the output off every other
clock cycle.
•
Under-voltage Lockout With
Hysteresis
•
•
Double Pulse Suppression
High Current Totem Pole
Output
•
Internally Trimmed Bandgap
Reference
•
•
500khz Operation
Low RO Error Amp
BLOCK DIAGRAM
Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.
Note 2: Toggle flip flop used only in 1844 and 1845.
4/97
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UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30V
Supply Voltage (ICC <30mA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self Limiting
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1A
Output Energy (Capacitive Load). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5µJ
Analog Inputs (Pins 2, 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6.3V
Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
Power Dissipation at TA ≤ 25°C (DIL-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W
Power Dissipation at TA ≤ 25°C (SOIC-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725mW
Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300°C
Note 1: All voltages are with respect to Pin 5.
All currents are positive into the specified terminal.
Consult Packaging Section of Databook for thermal limitations and considerations
of packages.
CONNECTION DIAGRAMS
DIL-8, SOIC-8 (TOP VIEW)
N or J Package, D8 Package
PLCC-20 (TOP VIEW)
Q Package
PACKAGE PIN FUNCTION
FUNCTION
PIN
1
N/C
COMP
N/C
2
3
N/C
4
VFB
5
N/C
6
ISENSE
N/C
7
8
N/C
9
SOIC-14 (TOP VIEW)
D Package
RT/CT
N/C
10
11
12
13
14
15
16
17
18
19
20
PWR GND
GROUND
N/C
OUTPUT
N/C
VC
VCC
N/C
VREF
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2
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
Unless otherwise stated, these specifications apply for -55°C ≤ TA ≤ 125°C for the
UC184X; -40°C ≤ TA ≤ 85°C for the UC284X; 0°C ≤ TA ≤ 70°C for the 384X; VCC =
15V (Note 5); RT = 10k; CT =3.3nF, TA=TJ.
ELECTRICAL CHARACTERISTICS:
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
UNITS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temp. Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short Circuit
Oscillator Section
Initial Accuracy
Voltage Stability
Temp. Stability
Amplitude
TJ = 25°C, IO = 1mA
12 ≤ VIN ≤ 25V
4.95
4.9
5.00
6
5.05
20
4.90
4.82
5.00
6
5.10
20
V
mV
mV
1 ≤ I0 ≤ 20mA
6
25
6
25
(Note 2) (Note 7)
0.2
0.4
5.1
0.2
0.4 mV/°C
Line, Load, Temp. (Note 2)
10Hz ≤ f ≤ 10kHz, TJ = 25°C (Note2)
TA = 125°C, 1000Hrs. (Note 2)
5.18
V
50
5
50
5
µV
mV
mA
25
25
-30
47
-100
-180
-30
47
-100
-180
TJ = 25°C (Note 6)
52
0.2
5
57
1
52
0.2
5
57
1
kHz
%
12 ≤ VCC ≤ 25V
TMIN ≤ TA ≤ TMAX (Note 2)
VPIN 4 peak to peak (Note 2)
%
1.7
1.7
V
Error Amp Section
Input Voltage
VPIN 1 = 2.5V
2.45
2.50
-0.3
90
1
2.55
-1
2.42
2.50
-0.3
90
1
2.58
-2
V
µA
dB
MHz
dB
mA
mA
V
Input Bias Current
AVOL
2 ≤ VO ≤ 4V
65
0.7
60
2
65
0.7
60
2
Unity Gain Bandwidth
PSRR
(Note 2) TJ = 25°C
12 ≤ VCC ≤ 25V
70
6
70
6
Output Sink Current
Output Source Current
VOUT High
VPIN 2 = 2.7V, VPIN 1 = 1.1V
VPIN 2 = 2.3V, VPIN 1 = 5V
VPIN 2 = 2.3V, RL = 15k to ground
VPIN 2 = 2.7V, RL = 15k to Pin 8
-0.5
5
-0.8
6
-0.5
5
-0.8
6
VOUT Low
0.7
1.1
0.7
1.1
V
Current Sense Section
Gain
(Notes 3 and 4)
2.85
0.9
3
1
3.15
1.1
2.85
0.9
3
1
3.15
1.1
V/V
V
Maximum Input Signal
PSRR
VPIN 1 = 5V (Note 3)
12 ≤ VCC ≤ 25V (Note 3) (Note 2)
70
-2
70
-2
dB
µA
ns
Input Bias Current
Delay to Output
-10
-10
VPIN 3 = 0 to 2V (Note 2)
150
300
150
300
Note 2: These parameters, although guaranteed, are not 100% tested in production.
Note 3: Parameter measured at trip point of latch with VPIN 2 = 0.
Note 4: Gain defined as
∆ VPIN 1
A =
, 0 ≤ VPIN 3 ≤ 0.8V
∆ VPIN 3
Note 5: Adjust VCC above the start threshold before setting at 15V.
Note 6: Output frequency equals oscillator frequency for the UC1842 and UC1843.
Output frequency is one half oscillator frequency for the UC1844 and UC1845.
Note 7: Temperature stability, sometimes referred to as average temperature coefficient, is described by the equation:
REF (max) − VREF (min)
V
Temp Stability =
TJ (max) − TJ (min)
VREF (max) and VREF (min) are the maximum and minimum reference voltages measured over the appropriate
temperature range. Note that the extremes in voltage do not necessarily occur at the extremes in temperature.
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3
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
Unless otherwise stated, these specifications apply for −55°C ≤ TA ≤ 125°C for the
UC184X; −40°C≤ TA ≤ 85°C for the UC284X; 0°C ≤ TA ≤ 70°C for the 384X; VCC =
15V (Note 5); RT = 10k; CT =3.3nF, TA=TJ.
ELECTRICAL CHARACTERISTICS:
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
UNITS
PARAMETER
TEST CONDITION
MIN
TYP
MAX
MIN
TYP
MAX
Output Section
Output Low Level
ISINK = 20mA
ISINK = 200mA
0.1
1.5
0.4
2.2
0.1
1.5
0.4
2.2
V
V
Output High Level
ISOURCE = 20mA
13
12
13.5
13.5
50
13
12
13.5
13.5
50
V
ISOURCE = 200mA
V
Rise Time
TJ = 25°C, CL = 1nF (Note 2)
TJ = 25°C, CL = 1nF (Note 2)
150
150
150
150
ns
ns
Fall Time
50
50
Under-voltage Lockout Section
Start Threshold
X842/4
X843/5
X842/4
X843/5
15
7.8
9
16
8.4
10
17
9.0
11
14.5
7.8
16
8.4
10
17.5
9.0
V
V
V
V
Min. Operating Voltage
After Turn On
8.5
11.5
8.2
7.0
7.6
8.2
7.0
7.6
PWM Section
Maximum Duty Cycle
X842/3
X844/5
95
46
97
48
100
50
0
95
47
97
48
100
50
0
%
%
%
Minimum Duty Cycle
Total Standby Current
Start-Up Current
0.5
11
34
1
0.5
11
34
1
mA
mA
V
Operating Supply Current
VCC Zener Voltage
VPIN 2 = VPIN 3 = 0V
ICC = 25mA
17
17
30
30
Note 2: These parameters, although guaranteed, are not 100% tested in production.
Note 3: Parameter measured at trip point of latch with VPIN 2 = 0.
Note 4: Gain defined as:
∆ VPIN 1
A =
; 0 ≤ VPIN 3 ≤ 0.8V.
∆ VPIN 3
Note 5: Adjust VCC above the start threshold before setting at 15V.
Note 6: Output frequency equals oscillator frequency for the UC1842 and UC1843.
Output frequency is one half oscillator frequency for the UC1844 and UC1845.
ERROR AMP CONFIGURATION
Error Amp can Source or Sink up to 0.5mA
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UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
UNDER-VOLTAGE LOCKOUT
During under-voltage lock-out, the output driver is biased to ground with a bleeder resistor to prevent activating the power
sink minor amounts of current. Pin 6 should be shunted to switch with extraneous leakage currents.
CURRENT SENSE CIRCUIT
Peak Current (IS) is Determined By The Formula
1.0V
ISMAX ≈
RS
A small RC filter may be required to suppress switch transients.
OSCILLATOR SECTION
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5
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
ERROR AMPLIFIER OPEN-LOOP
FREQUENCY RESPONSE
OUTPUT SATURATION CHARACTERISTICS
OPEN-LOOP LABORATORY FIXTURE
High peak currents associated with capacitive loads necessi- ground. The transistor and 5k potentiometer are used to sam-
tate careful grounding techniques. Timing and bypass capaci- ple the oscillator waveform and apply an adjustable ramp to
tors should be connected close to pin 5 in a single point pin 3.
SHUT DOWN TECHNIQUES
Shutdown of the UC1842 can be accomplished by two meth- pin 1 and/or 3 is removed. In one example, an externally
ods; either raise pin 3 above 1V or pull pin 1 below a voltage latched shutdown may be accomplished by adding an SCR
two diode drops above ground. Either method causes the out- which will be reset by cycling VCC below the lower UVLO
put of the PWM comparator to be high (refer to block diagram). threshold. At this point the reference turns off, allowing the
The PWM latch is reset dominant so that the output will remain SCR to reset.
low until the next clock cycle after the shutdown condition at
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UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
OFFLINE FLYBACK REGULATOR
5. Output Voltage:
Power Supply Specifications
A. +5V, ±5%; 1A to 4A load
Ripple voltage: 50mV P-P Max
1. Input Voltage
95VAC to 130VA
(50 Hz/60Hz)
3750V
B. +12V, ±3%; 0.1A to 0.3A load
2. Line Isolation
Ripple voltage: 100mV P-P Max
3. Switching Frequency
40kHz
C. -12V ,±3%; 0.1A to 0.3A load
4. Efficiency @ Full Load 70%
Ripple voltage: 100mV P-P Max
SLOPE COMPENSATION
A fraction of the oscillator ramp can be resistively
summed with the current sense signal to provide slope
compensation for converters requiring duty cycles over
50%.
Note that capacitor, C forms a filter with R2 to suppress
the leading edge switch spikes.
UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
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