Order this document by UC3844/D
UC3844, 45
UC2844, 45
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
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
14
1
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
(Top View)
8
7
6
5
Vref
VCC
Output
Gnd
•
•
•
•
•
•
•
•
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
Compensation
NC
Voltage Feedback
NC
Current Sense
1
2
3
4
5
6
7
(Top View)
14 Vref
13 NC
12 VCC
11 VC
10 Output
9
8
Gnd
Power Ground
Simplified Block Diagram
VCC
Vref
8(14)
R
R
RTCT
4(7)
Voltage
Feedback
2(3)
1(1)
Output
Comp.
Vref
Undervoltage
Lockout
Oscillator
Flip
Flop
&
Latching
PWM
5.0V
Reference
7(12)
NC
RT/CT
VCC
Undervoltage
Lockout
VC
7(11)
Output
6(10)
PWR GND
5(8)
Current
Sense
3(5)
ORDERING INFORMATION
Device
UC3844D
UC3845D
UC3844N
UC3845N
UC2844D
UC2845D
TA = – 25° to +85°C
TA = 0° to +70°C
Operating
Temperature Range
Package
SO–14
SO–14
Plastic
Plastic
SO–14
SO–14
Plastic
Plastic
Rev 1
+
–
Error
Amplifier
Gnd
5(9)
UC2844N
UC2845N
Pin numbers in parenthesis are for the D suffix SO–14 package.
©
Motorola, Inc. 1996
MOTOROLA ANALOG IC DEVICE DATA
1
UC3844, 45 UC2844, 45
MAXIMUM RATINGS
Rating
Total Power Supply and Zener Current
Output Current, Source or Sink (Note 1)
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, Case 751A
Maximum Power Dissipation @ TA = 25°C
Thermal Resistance Junction–to–Air
N Suffix, Plastic Package, Case 626
Maximum Power Dissipation @ TA = 25°C
Thermal Resistance Junction–to–Air
Operating Junction Temperature
Operating Ambient Temperature
UC3844, UC3845
UC2844, UC2845
Storage Temperature Range
Symbol
(ICC + IZ)
IO
W
Vin
IO
Value
30
1.0
5.0
– 0.3 to + 5.5
10
Unit
mA
A
µJ
V
mA
PD
R
θJA
PD
R
θJA
TJ
TA
862
145
1.25
100
+ 150
0 to + 70
– 25 to + 85
mW
°C/W
W
°C/W
°C
°C
Tstg
– 65 to + 150
°C
ELECTRICAL CHARACTERISTICS
(VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3],
unless otherwise noted.)
UC284X
Characteristics
REFERENCE SECTION
Reference Output Voltage (IO = 1.0 mA, TJ = 25°C)
Line Regulation (VCC = 12 V to 25 V)
Load Regulation (IO = 1.0 mA to 20 mA)
Temperature Stability
Total Output Variation over Line, Load, Temperature
Output Noise Voltage (f = 10 Hz to kHz, TJ = 25°C)
Long Term Stability (TA = 125°C for 1000 Hours)
Output Short Circuit Current
OSCILLATOR SECTION
Frequency
TJ = 25°C
TA = Tlow to Thigh
Frequency Change with Voltage (VCC = 12 V to 25 V)
Frequency Change with Temperature
TA = Tlow to Thigh
Oscillator Voltage Swing (Peak–to–Peak)
Discharge Current (Vosc = 2.0 V, TJ = 25°C)
fosc
47
46
∆f
osc/
∆
V
∆f
osc/
∆
T
Vosc
Idischg
–
–
–
–
52
–
0.2
5.0
1.6
10.8
57
60
1.0
–
–
–
47
46
–
–
–
–
52
–
0.2
5.0
1.6
10.8
57
60
1.0
–
–
–
%
%
V
mA
kHz
Vref
Regline
Regload
TS
Vref
Vn
S
ISC
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
µV
mV
mA
Symbol
Min
Typ
Max
Min
UC384X
Typ
Max
Unit
NOTES:
1. Maximum Package power dissipation limits must be observed.
2. Adjust VCC above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
Tlow =
–20°C
for UC3844, UC3845
Thigh = +70°C for UC3844, UC3845
Tlow =
–25°C for UC2844, UC2845
Thigh =
+85°C for UC2844, UC2845
2
MOTOROLA ANALOG IC DEVICE DATA
UC3844, 45 UC2844, 45
ELECTRICAL CHARACTERISTICS
(VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3],
unless otherwise noted,)
UC284X
Characteristics
ERROR AMPLIFIER SECTION
Voltage Feedback Input (VO = 2.5 V)
Input Bias Current (VFB = 2.7 V)
Open Loop Voltage Gain (VO = 2.0 V to 4.0 V)
Unity Gain Bandwidth (TJ = 25°C)
Power Supply Rejection Ratio (VCC = 12 V to 25 V)
Output Current
Sink (VO = 1.1 V, VFB = 2.7 V)
Source (VO = 5.0 V, VFB = 2.3 V)
Output Voltage Swing
High State (RL = 15 k to ground, VFB = 2.3 V)
Low State (RL = 15 k to Vref, VFB = 2.7 V)
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)
Maximum Current Sense Input Threshold (Note 4)
Power Supply Rejection Ratio
VCC = 12 V to 25 V (Note 4)
Input Bias Current
Propagation Delay (Current Sense Input to Output)
OUTPUT SECTION
Output Voltage
Low State (ISink = 20 mA)
(ISink = 200 mA)
High State (ISink = 20 mA)
(ISink = 200 mA)
Output Voltage with UVLO Activated
VCC = 6.0 V, ISink = 1.0 mA
Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C)
Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C)
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
UCX844
UCX845
Minimum Operating Voltage After Turn–On
UCX844
UCX845
PWM SECTION
Duty Cycle
Maximum
Minimum
TOTAL DEVICE
Power Supply Current (Note 2)
Startup:
(VCC = 6.5 V for UCX845A,
(VCC
14 V for UCX844) Operating
Power Supply Zener Voltage (ICC = 25 mA)
ICC
–
–
VZ
30
0.5
12
36
1.0
17
–
–
–
30
0.5
12
36
1.0
17
–
V
mA
%
DCmax
DCmin
46
–
48
–
50
0
47
–
48
–
50
0
Vth
15
7.8
VCC(min)
9.0
7.0
10
7.6
11
8.2
8.5
7.0
10
7.6
11.5
8.2
16
8.4
17
9.0
14.5
7.8
16
8.4
17.5
9.0
V
V
V
VOL
VOH
VOL(UVLO)
–
tr
tf
–
–
0.1
50
50
1.1
150
150
–
–
–
0.1
50
50
1.1
150
150
ns
ns
–
–
12
12
0.1
1.6
13.5
13.4
0.4
2.2
–
–
–
–
13
12
0.1
1.6
13.5
13.4
0.4
2.2
–
–
V
AV
Vth
PSRR
–
IIB
tPLH(IN/OUT)
–
–
70
–2.0
150
–
–10
300
–
–
–
70
–2.0
150
–
–10
300
µA
ns
2.85
0.9
3.0
1.0
3.15
1.1
2.85
0.9
3.0
1.0
3.15
1.1
V/V
V
dB
VFB
IIB
AVOL
BW
PSRR
ISink
ISource
VOH
VOL
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
2.58
–2.0
–
–
–
–
–
V
–
1.1
V
µA
dB
MHz
dB
mA
Symbol
Min
Typ
Max
Min
UC384X
Typ
Max
Unit
NOTES:
2. Adjust VCC above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
Tlow =
–20°C
for UC3844, UC3845
Thigh = +70°C for UC3844, UC3845
Tlow =
–25°C for UC2844, UC2845
Thigh =
+85°C for UC2844, UC2845
4. This parameter is measured at the latch trip point with VFB = 0 V.
∆V
Output Compensation
5. Comparator gain is defined as: AV
∆V
Current Sense Input
MOTOROLA ANALOG IC DEVICE DATA
3
UC3844, 45 UC2844, 45
Figure 1. Timing Resistor versus
Oscillator Frequency
100
% DT, PERCENT OUTPUT DEADTIME
RT, TIMING RESISTOR (k
Ω
)
50
20
10
5.0
2.0
VCC = 15 V
TA = 25°C
Figure 2. Output Deadtime versus
Oscillator Frequency
75
70
65
CT = 10 nF
5.0 nF
1.0 nF
2.0 nF
60
55
50
10 k
500 pF
NOTE: Output switches
at one–half the oscillator
frequency.
100 pF
200 pF
1.0
10 k
20 k
50 k
100 k
200 k
500 k
1.0 M
20 k
50 k
100 k
200 k
500 k
1.0 M
fosc, OSCILLATOR FREQUENCY (Hz)
fosc, OSCILLATOR FREQUENCY (Hz)
Figure 3. Error Amp Small Signal
Transient Response
VCC = 15 V
AV = –1.0
TA = 25°C
Figure 4. Error Amp Large Signal
Transient Response
VCC = 15 V
AV = –1.0
TA = 25°C
2.55 V
3.0 V
20 mV/DIV
2.5 V
2.5 V
2.45 V
0.5
µs/DIV
2.0 V
1.0
µs/DIV
Figure 5. Error Amp Open Loop Gain and
Phase versus Frequency
Vth, CURRENT SENSE INPUT THRESHOLD (V)
A VOL , OPEN LOOP VOLTAGE GAIN (dB)
100
80
Gain
60
40
Phase
20
0
– 20
10
120
150
100
1.0 k
10 k
100 k
1.0 M
180
10 M
VCC = 15 V
VO = 2.0 V to 4.0 V
RL = 100 K
TA = 25°C
0
30
60
90
φ
EXCESS PHASE (DEGREES)
,
1.2
Figure 6. Current Sense Input Threshold
versus Error Amp Output Voltage
VCC = 15 V
1.0
0.8
0.6
TA = 125°C
0.4
0.2
0
TA = –55°C
TA = 25°C
0
f, FREQUENCY (Hz)
2.0
4.0
6.0
VO, ERROR AMP OUTPUT VOLTAGE (V)
8.0
4
MOTOROLA ANALOG IC DEVICE DATA
200 mV/DIV
UC3844, 45 UC2844, 45
Figure 7. Reference Voltage Change
versus Source Current
0
VCC = 15 V
I SC , REFERENCE SHORT CIRCUIT CURRENT (mA)
∆
V ref , REFERENCE VOLTAGE CHANGE (mV)
Figure 8. Reference Short Circuit Current
versus Temperature
110
VCC = 15 V
RL
≤
0.1
Ω
90
–4.0
–8.0
–12
–16
–20
–24
0
20
40
60
80
100
120
Iref, REFERENCE SOURCE CURRENT (mA)
TA = 125°C
TA = 25°C
70
TA = –55°C
50
–55
–25
0
25
50
75
100
125
TA, AMBIENT TEMPERATURE (°C)
Figure 9. Reference Load Regulation
∆
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
∆
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
Figure 10. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
O
O
2.0 ms/DIV
2.0 ms/DIV
Figure 11. Output Saturation Voltage
versus Load Current
V sat , OUTPUT SATURATION VOLTAGE (V)
0
VCC
Source Saturation
(Load to Ground)
VCC = 15 V
80
µs
Pulsed Load
120 Hz Rate
Figure 12. Output Waveform
VCC = 15 V
CL = 1.0 nF
TA = 25°C
–1.0
–2.0
TA = 25°C
TA = –55°C
90%
3.0
TA = –55°C
2.0
1.0
0
0
200
Sink Saturation
(Load to VCC)
TA = 25°C
10%
Gnd
400
600
800
50 ns/DIV
IO, OUTPUT LOAD CURRENT (mA)
MOTOROLA ANALOG IC DEVICE DATA
5
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