Order this document by UC3844B/D
UC3844B, 45B
UC2844B, 45B
High Performance
Current Mode Controllers
The UC3844B, UC3845B 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
from 50% to 70%.
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 UCX844B has UVLO thresholds of 16 V (on) and 10 V (off), ideally
suited for off–line converters. The UCX845B is tailored for lower voltage
applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).
•
Trimmed Oscillator for Precise Frequency Control
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
D1 SUFFIX
PLASTIC PACKAGE
CASE 751
(SO–8)
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
8
1
14
1
•
•
•
•
•
•
•
•
•
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
Compensation
1
NC
2
Voltage Feedback
3
NC
4
Current Sense
5
NC
6
Compensation
1
Voltage Feedback
2
Current Sense
3
RT/CT
4
(Top View)
14
V
ref
13
NC
12
VCC
11
8
7
6
5
PIN CONNECTIONS
Vref
VCC
Output
Gnd
VC
Gnd
Power Ground
10
Output
9
8
Simplified Block Diagram
VCC
7(12)
RT/CT
7
(Top View)
Vref
8(14)
R
R
Vref
Undervoltage
Lockout
5.0V
Reference
VCC
Undervoltage
Lockout
ORDERING INFORMATION
Device
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Operating
Temperature Range
Package
SO–14
UC384XBD
UC384XBD1
UC384XBN
UC284XBD
UC284XBD1
UC284XBN
UC384XBVD
UC384XBVD1 TA = – 40° to +105°C
UC384XBVN
X indicates either a 4 or 5 to define specific device
part numbers.
©
Motorola, Inc. 1996
TA = 0° to + 70°C
SO–8
Plastic
SO–14
RT/CT
4(7)
Voltage
Feedback
Input
Output/
Compensation
1(1)
Oscillator
Latching
PWM
TA = – 25° to + 85°C
SO–8
Plastic
SO–14
SO–8
Plastic
2(3)
Error
Amplifier
3(5)
Gnd
5(9)
Current
Sense Input
Pin numbers in parenthesis are for the D suffix SO–14 package.
Rev 1
MOTOROLA ANALOG IC DEVICE DATA
1
UC3844B, 45B UC2844B, 45B
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, SO–14 Case 751A
Maximum Power Dissipation @ TA = 25°C
Thermal Resistance, Junction–to–Air
D1 Suffix, Plastic Package, SO–8 Case 751
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
UC3844B, UC3845B
UC2844B, UC2845B
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
PD
R
θJA
TJ
TA
862
145
702
178
1.25
100
+150
0 to + 70
– 25 to + 85
mW
°C/W
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. For typical values TA = 25°C, for min/max values TA is
the operating ambient temperature range that applies [Note 3], unless otherwise noted.)
UC284XB
Characteristic
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, and Temperature
Output Noise Voltage (f = 10 Hz to 10 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
TJ = 25°C (RT = 6.2 k, CT = 1.0 nF)
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
TA = Tlow to Thigh (UC284XB, UC384XB)
TA = Tlow to Thigh
(UC384XBV)
fOSC
49
48
225
∆f
OSC/∆V
∆f
OSC/∆T
VOSC
Idischg
7.8
7.5
–
8.3
–
–
8.8
8.8
–
7.8
7.6
7.2
8.3
–
–
8.8
8.8
8.8
–
–
–
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
–
–
%
%
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
UC384XB, XBV
Min
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 = 0°C for UC3844B, UC3845B
Thigh = + 70°C for UC3844B, UC3845B
= – 25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
= – 40°C for UC3844BV, UC3845BV
= +105°C for UC3844BV, UC3845BV
2
MOTOROLA ANALOG IC DEVICE DATA
UC3844B, 45B UC2844B, 45B
ELECTRICAL CHARACTERISTICS
(VCC = 15 V [Note 2], 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 3], unless otherwise noted.)
UC284XB
Characteristic
ERROR AMPLIFIER SECTION
Voltage Feedback Input (VO = 2.5 V)
Input Bias Current (VFB = 5.0 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)
(UC284XB, UC384XB)
(UC384XBV)
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)
(UC284XB, UC384XB)
(UC384XBV)
Maximum Current Sense Input Threshold (Note 4)
(UC284XB, UC384XB)
(UC384XBV)
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, UC284XB, UC384XB)
(ISink = 200 mA, UC384XBV)
High State (ISource = 20 mA, UC284XB, UC384XB)
(ISource = 20 mA, UC384XBV)
(ISource = 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
UCX844B, BV
UCX845B, BV
Minimum Operating Voltage After Turn–On
UCX844B, BV
UCX845B, BV
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
–
–
–
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
AV
2.85
–
Vth
0.9
–
PSRR
IIB
tPLH(In/Out)
–
–
–
1.0
–
70
– 2.0
150
1.1
–
–
–10
300
0.9
0.85
–
–
–
1.0
1.0
70
– 2.0
150
1.1
1.1
–
–10
300
dB
µA
ns
3.0
–
3.15
–
2.85
2.85
3.0
3.0
3.15
3.25
V
V/V
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
0.8
2.58
– 2.0
–
–
–
–
–
V
–
1.1
1.2
V
µA
dB
MHz
dB
mA
Symbol
Min
Typ
Max
UC384XB, XBV
Min
Typ
Max
Unit
VOH
VOL(UVLO)
tr
tf
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 = 0°C for UC3844B, UC3845B
Thigh = + 70°C for UC3844B, UC3845B
Tlow
= – 25°C for UC2844B, UC2845B
T
high
= + 85°C for UC2844B, UC2845B
Tlow
= – 40°C for UC3844BV, UC3845BV
Th igh
= +105°C for UC3844BV, UC3845BV
4. This parameter is measured at the latch trip point with VFB = 0 V.
5. Comparator gain is defined as: AV =
D
V Output Compensation
D
V Current Sense Input
MOTOROLA ANALOG IC DEVICE DATA
3
UC3844B, 45B UC2844B, 45B
ELECTRICAL CHARACTERISTICS
(VCC = 15 V [Note 2], 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 3], unless otherwise noted.)
UC284XB
Characteristic
PWM SECTION
Duty Cycle
Maximum (UC284XB, UC384XB)
Maximum
(UC384XBV)
Minimum
TOTAL DEVICE
Power Supply Current
Startup (VCC = 6.5 V for UCX845B,
Start–Up (VCC
14 V for UCX844B, BV)
Operating (Note 2)
Power Supply Zener Voltage (ICC = 25 mA)
ICC
–
–
VZ
30
0.3
12
36
0.5
17
–
–
–
30
0.3
12
36
0.5
17
–
V
mA
%
DC(max)
DC(min)
47
–
–
48
–
–
50
–
0
47
46
–
48
48
–
50
50
0
Symbol
Min
Typ
Max
UC384XB, XBV
Min
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 = 0°C for UC3844B, UC3845B
Thigh = + 70°C for UC3844B, UC3845B
= – 25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
= – 40°C for UC3844BV, UC3845BV
= +105°C for UC3844BV, UC3845BV
Figure 1. Timing Resistor
versus Oscillator Frequency
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
fOSC, OSCILLATOR FREQUENCY (kHz)
1.0 M
% DT, PERCENT OUTPUT DEADTIME
VCC = 15 V
TA = 25°C
75
70
65
60
55
1.
2.
3.
4.
5.
6.
7.
Figure 2. Output Deadtime
versus Oscillator Frequency
50
10 k
Figure 3. Error Amp Small Signal
Transient Response
2.55 V
VCC = 15 V
AV = –1.0
TA = 25°C
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
4
MOTOROLA ANALOG IC DEVICE DATA
200 mV/DIV
ÄÄÄÄ
ÄÄÄÄ
ÄÄÄÄ
ÄÄÄÄ
ÄÄÄÄ
CT = 10 nF
CT = 5.0 nF
CT = 2.0 nF
CT = 1.0 nF
CT = 500 pF
CT = 200 pF
CT = 100 pF
20 k
3
2
1
4
7
5
6
50 k 100 k
200 k
500 k
fOSC, OSCILLATOR FREQUENCY (kHz)
1.0 M
Figure 4. Error Amp Large Signal
Transient Response
VCC = 15 V
AV = –1.0
TA = 25°C
UC3844B, 45B UC2844B, 45B
Figure 5. Error Amp Open Loop Gain and
Phase versus Frequency
A VOL , OPEN LOOP VOLTAGE GAIN (dB)
100
80
Gain
60
40
Phase
20
0
– 20
10
VCC = 15 V
VO = 2.0 V to 4.0 V
RL = 100 k
TA = 25°C
0
φ
, EXCESS PHASE (DEGREES)
30
60
90
Vth , CURRENT SENSE INPUT THRESHOLD (V)
Figure 6. Current Sense Input Threshold
versus Error Amp Output Voltage
1.2
VCC = 15 V
1.0
0.8
TA = 25°C
0.6
TA = 125°C
0.4
TA = – 55°C
0.2
0
120
150
180
10 M
100
1.0 k
10 k
100 k
f, FREQUENCY (Hz)
1.0 M
0
2.0
4.0
6.0
VO, ERROR AMP OUTPUT VOLTAGE (VO)
8.0
ISC , REFERENCE SHORT CIRCUIT CURRENT (mA)
∆
Vref , REFERENCE VOLTAGE CHANGE (mV)
Figure 7. Reference Voltage Change
versus Source Current
0
VCC = 15 V
– 4.0
– 8.0
– 12
TA = 125°C
– 16
– 20
TA = 25°C
– 24
0
20
40
60
80
100
Iref, REFERENCE SOURCE CURRENT (mA)
120
TA = – 55°C
Figure 8. Reference Short Circuit Current
versus Temperature
90
70
50
– 55
– 25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
∆
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 9. Reference Load Regulation
Figure 10. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
2.0 ms/DIV
2.0 ms/DIV
MOTOROLA ANALOG IC DEVICE DATA
ÄÄÄÄ
ÄÄÄÄ
VCC = 15 V
RL
≤
0.1
Ω
100
125
110
O
O
5
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