The UC3844B, UC3845B series are high performance fixed frequency
current mode controllers. They are specifically designed for Off−Line
and dc−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 from 50% to 70%.
These devices are available in an 8−pin dual−in−line and surface
mount (SOIC−8) plastic package as well as the 14−pin plastic surface
mount (SOIC−14). The SOIC−14 package has separate power and
ground pins for the totem pole output stage.
The UCX844B has UVLO thresholds of 16V (on) and 10V (off), ideally
suited for off−line converters. The UCX845B is tailored for lower voltage
applications having UVLO thresholds of 8.5V (on) and 7.6V (off).
Features
UC3844B, UC3845B,
UC2844B, UC2845B
High Performance
Current Mode Controllers
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8
1
PDIP−8
N SUFFIX
CASE 626
14
1
SOIC−14
D SUFFIX
CASE 751A
8
1
•
•
•
•
•
•
•
•
•
•
•
•
SOIC−8
D1 SUFFIX
CASE 751
Trimmed Oscillator for Precise Frequency Control
Oscillator Frequency Guaranteed at 250 kHz
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
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
These Devices are Pb−Free and are RoHS Compliant
NCV Prefix for Automotive and Other Applications Requiring
Unique Site and Control Change Requirements; AEC−Q100
Qualified and PPAP Capable
V
CC
7(12)
V
CC
Undervoltage
Lockout
V
C
7(11)
Output
Oscillator
Latching
PWM
6(10)
Power
Ground
5(8)
Current
Sense Input
3(5)
GND
5(9)
PIN CONNECTIONS
Compensation
Voltage Feedback
Current Sense
R
T
/C
T
1
2
3
4
8
7
6
5
(Top View)
Compensation
NC
Voltage Feedback
NC
Current Sense
NC
R
T
/C
T
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
ref
V
CC
Output
GN
D
V
ref
NC
V
CC
V
C
Output
GND
Power Ground
V
ref
8(14)
R
R
V
ref
Undervoltage
Lockout
5.0V
Reference
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 15 of this data sheet.
R
T
/C
T
4(7)
Voltage
Feedback
Input
2(3)
Output/
Compensation
1(1)
Error
Amplifier
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 16 of this data sheet.
Pin numbers in parenthesis are for the D suffix SOIC-14 package.
Figure 1. Simplified Block Diagram
©
Semiconductor Components Industries, LLC, 2012
December, 2012
−
Rev. 11
1
Publication Order Number:
UC3844B/D
UC3844B, UC3845B, UC2844B, UC2845B
MAXIMUM RATINGS
Rating
Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec) (Note 1)
Total Power Supply and Zener Current
Output Current, Source or Sink (Note 2)
Output Energy (Capacitive Load per Cycle)
Current Sense and Voltage Feedback Inputs
Error Amp Output Sink Current
Power Dissipation and Thermal Characteristics
D Suffix, Plastic Package, SOIC−14 Case 751A
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance, Junction−to−Air
D1 Suffix, Plastic Package, SOIC−8 Case 751
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance, Junction−to−Air
N Suffix, Plastic Package, Case 626
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance, Junction−to−Air
Operating Junction Temperature
Operating Ambient Temperature
UC3844B, UC3845B
UC2844B, UC2845B
UC3844BV, UC3845BV
Symbol
V
CC
, V
C
(I
CC
+ I
Z
)
I
O
W
V
in
I
O
Value
36
30
1.0
5.0
−
0.3 to + 5.5
10
Unit
V
mA
A
mJ
V
mA
P
D
R
qJA
P
D
R
qJA
P
D
R
qJA
T
J
T
A
862
145
702
178
1.25
100
+150
0 to +70
−25
to +85
−40
to +105
mW
°C/W
mW
°C/W
W
°C/W
°C
°C
Storage Temperature Range
T
stg
−
65 to +150
°C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
1. The voltage is clamped by a zener diode (see page 9 Under Voltage Lockout section). Therefore this voltage may be exceeded as long as
the total power supply and zener current is not exceeded.
2. Maximum package power dissipation limits must be observed.
3. This device series contains ESD protection and exceeds the following tests: Human Body Model 4000 V per JEDEC Standard
JESD22-A114B, Machine Model Method 200 V per JEDEC Standard JESD22-A115-A
4. This device contains latch-up protection and exceeds 100 mA per JEDEC Standard JESD78
T
A
is the operating ambient temperature range that applies [Note 6], unless otherwise noted.)
UC284xB
Characteristic
REFERENCE SECTION
Reference Output Voltage (I
O
= 1.0 mA, T
J
= 25°C)
Line Regulation (V
CC
= 12 V to 25 V)
Load Regulation (I
O
= 1.0 mA to 20 mA)
Temperature Stability
Total Output Variation over Line, Load, & Temperature
Output Noise Voltage (f = 10 Hz to 10 kHz, T
J
= 25°C)
Long Term Stability (T
A
= 125°C for 1000 Hours)
Output Short Circuit Current
OSCILLATOR SECTION
Frequency
T
J
= 25°C
T
A
= T
low
to T
high
T
J
= 25°C (R
T
= 6.2 k, C
T
= 1.0 nF)
f
OSC
49
48
225
−
−
−
52
−
250
0.2
1.0
1.6
55
56
275
1.0
−
−
49
48
225
−
−
−
52
−
250
0.2
0.5
1.6
55
56
275
1.0
−
−
kHz
V
ref
Reg
line
Reg
load
T
S
V
ref
V
n
S
I
SC
4.95
−
−
−
4.9
−
−
−
30
5.0
2.0
3.0
0.2
−
50
5.0
−
85
5.05
20
25
−
5.1
−
−
−180
4.9
−
−
−
4.82
−
−
−
30
5.0
2.0
3.0
0.2
−
50
5.0
−
85
5.1
20
25
−
5.18
−
−
−180
V
mV
mV
mV/°C
V
mV
mV
mA
Symbol
Min
Typ
Max
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V [Note 5], R
T
= 10 k, C
T
= 3.3 nF. For typical values T
A
= 25°C, for min/max values
UC384xB, xBV, NCV384xBV
Min
Typ
Max
Unit
Frequency Change with Voltage (V
CC
= 12 V to 25 V)
Frequency Change w/ Temperature (T
A
= T
low
to T
high
)
Oscillator Voltage Swing (Peak−to−Peak)
Df
OSC
/DV
Df
OSC
/DT
V
OSC
%
%
V
5. Adjust V
CC
above the Startup threshold before setting to 15 V.
6. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
= 0°C for UC3844B, UC3845B
T
high
= + 70°C for UC3844B, UC3845B
=
−
25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
=
−
40°C for UC384xBV, NCV384xBV
=+105°C for UC3844BV, UC3845BV
= +125°C for NCV384xBV
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2
UC3844B, UC3845B, UC2844B, UC2845B
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V [Note 7], R
T
= 10 k, C
T
= 3.3 nF. For typical values T
A
= 25°C, for min/max values
UC284xB
Characteristic
OSCILLATOR SECTION
Discharge Current (V
OSC
= 2.0 V)
T
A
= T
low
to T
high
ERROR AMPLIFIER SECTION
Voltage Feedback Input (V
O
= 2.5 V)
Input Bias Current (V
FB
= 5.0 V)
Open Loop Voltage Gain (V
O
= 2.0 V to 4.0 V)
Unity Gain Bandwidth (T
J
= 25°C)
Power Supply Rejection Ratio (V
CC
= 12 V to 25 V)
Output Current
−
Sink (V
O
= 1.1 V, V
FB
= 2.7 V)
Output Current
−
Source (V
O
= 5.0 V, V
FB
= 2.3 V)
Output Voltage Swing
High State (R
L
= 15 k to ground, V
FB
= 2.3 V)
Low State (R
L
= 15 k to V
ref
, V
FB
= 2.7 V)
(UC284XB, UC384XB)
(UC384XBV)
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 9 & 10)
(UC284XB, UC384XB)
(UC384XBV)
Maximum Current Sense Input Threshold (Note 9)
(UC284XB, UC384XB)
(UC384XBV)
Power Supply Rejection Ratio (V
CC
= 12 V to 25 V) (Note 9)
Input Bias Current
Propagation Delay (Current Sense Input to Output)
OUTPUT SECTION
Output Voltage
Low State (I
Sink
= 20 mA)
(I
Sink
= 200 mA, UC284XB, UC384XB)
(I
Sink
= 200 mA, UC384XBV)
High State (I
Source
= 20 mA, UC284XB, UC384XB)
(I
Source
= 20 mA, UC384XBV)
(I
Source
= 200 mA)
Output Voltage with UVLO Activated (V
CC
= 6.0 V, I
Sink
= 1.0 mA)
Output Voltage Rise Time (C
L
= 1.0 nF, T
J
= 25°C)
Output Voltage Fall Time (C
L
= 1.0 nF, T
J
= 25°C)
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
Minimum Operating Voltage After Turn−On
UCX844B, BV
UCX845B, BV
UCX844B, BV
UCX845B, BV
V
th
V
CC(min)
15
7.8
9.0
7.0
16
8.4
10
7.6
17
9.0
11
8.2
14.5
7.8
8.5
7.0
16
8.4
10
7.6
17.5
9.0
11.5
8.2
V
V
V
V
OL
V
OH
−
−
−
13
−
12
−
−
−
0.1
1.6
−
13.5
−
13.4
0.1
50
50
0.4
2.2
−
−
−
−
1.1
150
150
−
−
−
13
12.9
12
−
−
−
0.1
1.6
1.6
13.5
−
13.4
0.1
50
50
0.4
2.2
2.3
−
−
−
1.1
150
150
V
ns
ns
A
V
V/V
2.85
−
0.9
−
−
−
−
3.0
−
1.0
−
70
−
2.0
150
3.15
−
1.1
−
−
−10
300
2.85
2.85
0.9
0.85
−
−
−
3.0
3.0
1.0
1.0
70
−
2.0
150
3.15
3.25
V
1.1
1.1
−
−10
300
dB
mA
ns
V
FB
I
IB
A
VOL
BW
PSRR
I
Sink
I
Source
V
OH
V
OL
2.45
−
65
0.7
60
2.0
−
0.5
5.0
−
−
2.5
−
0.1
90
1.0
70
12
−1.0
6.2
0.8
−
2.55
−1.0
−
−
−
−
−
−
1.1
−
2.42
−
65
0.7
60
2.0
−
0.5
5.0
−
−
2.5
−
0.1
90
1.0
70
12
−1.0
6.2
0.8
0.8
2.58
−
2.0
−
−
−
−
−
−
1.1
1.2
V
mA
dB
MHz
dB
mA
V
T
J
= 25°C
(UC284XB, UC384XB)
(UC384XBV)
I
dischg
7.8
7.5
−
8.3
−
−
8.8
8.8
−
7.8
7.6
7.2
8.3
−
−
8.8
8.8
8.8
mA
Symbol
Min
Typ
Max
UC384xB, xBV,
NCV384xBV
Min
Typ
Max
Unit
T
A
is the operating ambient temperature range that applies [Note 8], unless otherwise noted.)
V
th
PSRR
I
IB
t
PLH(In/Out)
V
OL(UVLO)
t
r
t
f
7. Adjust V
CC
above the Startup threshold before setting to 15 V.
8. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
= 0°C for UC3844B, UC3845B
T
high
= + 70°C for UC3844B, UC3845B
=
−
25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
=
−
40°C for UC384xBV, NCV384xBV
= +105°C for UC3844BV, UC3845BV
= +125°C for NCV384xBV
9. This parameter is measured at the latch trip point with V
FB
= 0 V.
10. Comparator gain is defined as: A
V
=
DV
Output/Compensation
DV
Current Sense Input
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3
UC3844B, UC3845B, UC2844B, UC2845B
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V [Note 11], R
T
= 10 k, C
T
= 3.3 nF. For typical values T
A
= 25°C, for min/max
values T
A
is the operating ambient temperature range that applies [Note 12], unless otherwise noted.)
UC284xB
Characteristic
PWM SECTION
Duty Cycle
Maximum
Maximum
Minimum
%
(UC284XB, UC384XB)
(UC384XBV)
DC
(max)
DC
(min)
I
CC
47
−
−
48
−
−
50
−
0
47
46
−
48
48
−
50
50
0
mA
−
−
V
Z
30
0.3
12
36
0.5
17
−
−
−
30
0.3
12
36
0.5
17
−
V
Symbol
Min
Typ
Max
UC384xB, xBV, NCV384xBV
Min
Typ
Max
Unit
TOTAL DEVICE
Power Supply Current
Startup (V
CC
= 6.5 V for UCX845B,
Startup (V
CC
=
14 V for UCX844B, BV)
Operating (Note 11)
Power Supply Zener Voltage (I
CC
= 25 mA)
11. Adjust V
CC
above the Startup threshold before setting to 15 V.
12. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
= 0°C for UC3844B, UC3845B
T
high
= + 70°C for UC3844B, UC3845B
=
−
25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
=
−
40°C for UC384xBV, NCV384xBV
= +105°C for UC3844BV, UC3845BV
=+125°C for NCV384xBV
80
50
R T, TIMING RESISTOR (k
Ω
)
20
8.0
5.0
2.0
0.8
10 k
NOTE: Output switches at
1/2 the oscillator frequency
20 k
50 k
100 k
200 k
500 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
1.0 M
V
CC
= 15 V
T
A
= 25°C
75
% DT, PERCENT OUTPUT DEADTIME
70
65
60
55
50
10 k
For R
T
u
5 Kf
X
1.72
R
T
C
T
Figure 2. Timing Resistor
versus Oscillator Frequency
Figure 3. Output Deadtime
versus Oscillator Frequency
2.55 V
V
CC
= 15 V
A
V
= -1.0
T
A
= 25°C
3.0 V
20 mV/DIV
2.5 V
2.5 V
2.45 V
0.5
ms/DIV
2.0 V
1.0
ms/DIV
Figure 4. Error Amp Small Signal
Transient Response
Figure 5. Error Amp Large Signal
Transient Response
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4
200 mV/DIV
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
1.
2.
3.
4.
5.
6.
7.
C
T
= 10 nF
C
T
= 5.0 nF
C
T
= 2.0 nF
C
T
= 1.0 nF
C
T
= 500 pF
C
T
= 200 pF
C
T
= 100 pF
20 k
3
2
1
4
7
5
6
50 k 100 k
200 k
500 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
1.0 M
V
CC
= 15 V
A
V
= -1.0
T
A
= 25°C
UC3844B, UC3845B, UC2844B, UC2845B
A VOL , OPEN LOOP VOLTAGE GAIN (dB)
100
80
Gain
60
40
Phase
20
0
- 20
10
V
CC
= 15 V
V
O
= 2.0 V to 4.0 V
R
L
= 100 k
T
A
= 25°C
0
30
60
90
120
150
180
10 M
φ
, EXCESS PHASE (DEGREES)
Vth , CURRENT SENSE INPUT THRESHOLD (V)
1.2
V
CC
= 15 V
1.0
0.8
T
A
= 25°C
0.6
T
A
= 125°C
0.4
T
A
= - 55°C
0.2
0
100
1.0 k
10 k
100 k
f, FREQUENCY (Hz)
1.0 M
0
2.0
4.0
6.0
V
O
, ERROR AMP OUTPUT VOLTAGE (V
O
)
8.0
Figure 6. Error Amp Open Loop Gain and
Phase versus Frequency
Figure 7. Current Sense Input Threshold
versus Error Amp Output Voltage
V
CC
= 15 V
- 4.0
- 8.0
- 12
T
A
= 125°C
- 16
- 20
T
A
= 25°C
- 24
0
20
40
60
80
100
I
ref
, REFERENCE SOURCE CURRENT (mA)
120
T
A
= - 55°C
90
70
50
- 55
- 25
0
25
50
75
T
A
, AMBIENT TEMPERATURE (°C)
Figure 8. Reference Voltage Change
versus Source Current
Figure 9. Reference Short Circuit Current
versus Temperature
Δ
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
V
CC
= 15 V
I
O
= 1.0 mA to 20 mA
T
A
= 25°C
Δ
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
V
CC
= 12 V to 25 V
T
A
= 25°C
2.0 ms/DIV
2.0 ms/DIV
Figure 10. Reference Load Regulation
Figure 11. Reference Line Regulation
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5
ÄÄÄÄ
ÄÄÄÄ
V
CC
= 15 V
R
L
≤
0.1
W
100
125
0
ISC , REFERENCE SHORT CIRCUIT CURRENT (mA)
Δ
Vref , REFERENCE VOLTAGE CHANGE (mV)
110
O
O
单片机
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