Order this document by UC3844B/D
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
•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
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Simplified Block Diagram |
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VCC |
7(12) |
Vref |
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5.0V |
VCC |
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Undervoltage |
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Reference |
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8(14) |
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Lockout |
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R |
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Vref |
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VC |
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R |
Undervoltage |
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Lockout |
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7(11) |
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RT/CT |
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Oscillator |
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Output |
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6(10) |
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4(7) |
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Latching |
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Voltage |
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PWM |
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Power |
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Ground |
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Feedback |
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5(8) |
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Input |
Error |
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2(3) |
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Output/ |
Amplifier |
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Current |
Compensation |
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Sense Input |
1(1) |
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3(5) |
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO±14 package.
UC3844B, 45B UC2844B, 45B
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
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8 |
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1 |
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D1 SUFFIX |
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PLASTIC PACKAGE |
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CASE 751 |
8 |
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(SO±8) |
1 |
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D SUFFIX |
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PLASTIC PACKAGE |
14 |
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CASE 751A |
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1 |
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(SO±14) |
PIN CONNECTIONS
Compensation |
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Vref |
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1 |
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8 |
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Voltage Feedback |
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VCC |
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2 |
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7 |
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Current Sense |
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Output |
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3 |
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6 |
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RT/CT |
4 |
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Gnd |
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5 |
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(Top View) |
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Compensation |
1 |
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V |
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14 |
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ref |
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NC |
2 |
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13 |
NC |
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Voltage Feedback |
3 |
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12 |
VCC |
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NC |
4 |
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11 |
V |
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Current Sense |
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C |
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5 |
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10 |
Output |
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NC |
6 |
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9 |
Gnd |
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RT/CT |
7 |
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8 |
Power Ground |
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ORDERING INFORMATION |
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Device |
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Operating |
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Package |
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Temperature Range |
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UC384XBD |
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SO±14 |
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UC384XBD1 |
TA = 0° to + 70°C |
SO±8 |
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UC384XBN |
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Plastic |
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UC284XBD |
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SO±14 |
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TA = ± 25° to + 85°C |
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UC284XBD1 |
SO±8 |
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UC284XBN |
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Plastic |
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UC384XBVD |
TA = ± 40° to +105°C |
SO±14 |
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UC384XBVD1 |
SO±8 |
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UC384XBVN |
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Plastic |
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X indicates either a 4 or 5 to define specific device part numbers.
Motorola, Inc. 1996 Rev 1
UC3844B, 45B UC2844B, 45B
MAXIMUM RATINGS
Rating |
Symbol |
Value |
Unit |
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Total Power Supply and Zener Current |
(ICC + IZ) |
30 |
mA |
Output Current, Source or Sink (Note 1) |
IO |
1.0 |
A |
Output Energy (Capacitive Load per Cycle) |
W |
5.0 |
μJ |
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Current Sense and Voltage Feedback Inputs |
Vin |
± 0.3 to + 5.5 |
V |
Error Amp Output Sink Current |
IO |
10 |
mA |
Power Dissipation and Thermal Characteristics |
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D Suffix, Plastic Package, SO±14 Case 751A |
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Maximum Power Dissipation @ TA = 25°C |
PD |
862 |
mW |
Thermal Resistance, Junction±to±Air |
RθJA |
145 |
°C/W |
D1 Suffix, Plastic Package, SO±8 Case 751 |
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Maximum Power Dissipation @ TA = 25°C |
PD |
702 |
mW |
Thermal Resistance, Junction±to±Air |
RθJA |
178 |
°C/W |
N Suffix, Plastic Package, Case 626 |
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Maximum Power Dissipation @ TA = 25°C |
PD |
1.25 |
W |
Thermal Resistance, Junction±to±Air |
RθJA |
100 |
°C/W |
Operating Junction Temperature |
TJ |
+150 |
°C |
Operating Ambient Temperature |
TA |
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°C |
UC3844B, UC3845B |
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0 to + 70 |
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UC2844B, UC2845B |
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± 25 to + 85 |
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Storage Temperature Range |
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.)
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UC284XB |
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UC384XB, XBV |
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Characteristic |
Symbol |
Min |
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Typ |
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Max |
Min |
Typ |
Max |
Unit |
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REFERENCE SECTION |
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Reference Output Voltage (IO = 1.0 mA, TJ = 25°C) |
Vref |
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4.95 |
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5.0 |
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5.05 |
4.9 |
5.0 |
5.1 |
V |
Line Regulation (VCC = 12 V to 25 V) |
Regline |
± |
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2.0 |
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20 |
± |
2.0 |
20 |
mV |
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Load Regulation (IO = 1.0 mA to 20 mA) |
Regload |
± |
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3.0 |
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25 |
± |
3.0 |
25 |
mV |
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Temperature Stability |
TS |
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± |
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0.2 |
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0.2 |
± |
mV/°C |
Total Output Variation over Line, Load, and Temperature |
Vref |
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4.9 |
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± |
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5.1 |
4.82 |
± |
5.18 |
V |
Output Noise Voltage (f = 10 Hz to 10 kHz, TJ = 25°C) |
Vn |
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50 |
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50 |
± |
μV |
Long Term Stability (TA = 125°C for 1000 Hours) |
S |
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± |
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5.0 |
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± |
± |
5.0 |
± |
mV |
Output Short Circuit Current |
ISC |
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± 30 |
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± 85 |
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±180 |
± 30 |
± 85 |
±180 |
mA |
OSCILLATOR SECTION |
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Frequency |
fOSC |
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kHz |
TJ = 25°C |
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49 |
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52 |
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55 |
49 |
52 |
55 |
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TA = Tlow to Thigh |
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48 |
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± |
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56 |
48 |
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56 |
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TJ = 25°C (RT = 6.2 k, CT = 1.0 nF) |
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225 |
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250 |
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275 |
225 |
250 |
275 |
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Frequency Change with Voltage (VCC = 12 V to 25 V) |
fOSC/ |
V |
± |
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0.2 |
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1.0 |
± |
0.2 |
1.0 |
% |
Frequency Change with Temperature |
fOSC/ |
T |
± |
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1.0 |
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0.5 |
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% |
TA = Tlow to Thigh |
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Oscillator Voltage Swing (Peak±to±Peak) |
VOSC |
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± |
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1.6 |
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± |
± |
1.6 |
± |
V |
Discharge Current (VOSC = 2.0 V) |
Idischg |
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mA |
TJ = 25°C |
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7.8 |
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8.3 |
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8.8 |
7.8 |
8.3 |
8.8 |
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TA = Tlow to Thigh (UC284XB, UC384XB) |
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7.5 |
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± |
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8.8 |
7.6 |
± |
8.8 |
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(UC384XBV) |
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± |
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± |
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7.2 |
± |
8.8 |
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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 |
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± 40°C for UC3844BV, UC3845BV |
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+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.)
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UC284XB |
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UC384XB, XBV |
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Characteristic |
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Symbol |
Min |
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Typ |
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Max |
Min |
Typ |
Max |
Unit |
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ERROR AMPLIFIER SECTION |
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Voltage Feedback Input (VO = 2.5 V) |
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VFB |
2.45 |
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2.5 |
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2.55 |
2.42 |
2.5 |
2.58 |
V |
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Input Bias Current (VFB = 5.0 V) |
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IIB |
± |
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± 0.1 |
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±1.0 |
± |
± 0.1 |
± 2.0 |
μA |
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Open Loop Voltage Gain (VO = 2.0 V to 4.0 V) |
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AVOL |
65 |
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90 |
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± |
65 |
90 |
± |
dB |
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Unity Gain Bandwidth (TJ = 25°C) |
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BW |
0.7 |
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1.0 |
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± |
0.7 |
1.0 |
± |
MHz |
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Power Supply Rejection Ratio (VCC = 12 V to 25 V) |
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PSRR |
60 |
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70 |
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± |
60 |
70 |
± |
dB |
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Output Current |
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mA |
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Sink (VO = 1.1 V, VFB = 2.7 V) |
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ISink |
2.0 |
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12 |
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± |
2.0 |
12 |
± |
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Source (VO = 5.0 V, VFB = 2.3 V) |
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ISource |
± 0.5 |
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±1.0 |
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± |
± 0.5 |
±1.0 |
± |
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Output Voltage Swing |
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V |
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High State (RL = 15 k to ground, VFB = 2.3 V) |
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VOH |
5.0 |
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6.2 |
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± |
5.0 |
6.2 |
± |
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Low State (RL = 15 k to Vref, VFB = 2.7 V) |
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VOL |
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(UC284XB, UC384XB) |
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± |
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0.8 |
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1.1 |
± |
0.8 |
1.1 |
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(UC384XBV) |
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± |
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± |
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± |
± |
0.8 |
1.2 |
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CURRENT SENSE SECTION |
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Current Sense Input Voltage Gain (Notes 4 & 5) |
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AV |
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V/V |
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(UC284XB, UC384XB) |
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2.85 |
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3.0 |
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3.15 |
2.85 |
3.0 |
3.15 |
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(UC384XBV) |
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± |
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± |
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± |
2.85 |
3.0 |
3.25 |
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Maximum Current Sense Input Threshold (Note 4) |
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Vth |
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V |
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(UC284XB, UC384XB) |
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0.9 |
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1.0 |
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1.1 |
0.9 |
1.0 |
1.1 |
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(UC384XBV) |
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± |
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± |
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± |
0.85 |
1.0 |
1.1 |
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Power Supply Rejection Ratio |
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PSRR |
± |
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70 |
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± |
± |
70 |
± |
dB |
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(VCC = 12 V to 25 V) (Note 4) |
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Input Bias Current |
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IIB |
± |
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± 2.0 |
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±10 |
± |
± 2.0 |
±10 |
μA |
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Propagation Delay (Current Sense Input to Output) |
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tPLH(In/Out) |
± |
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150 |
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300 |
± |
150 |
300 |
ns |
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OUTPUT SECTION |
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Output Voltage |
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V |
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Low State |
(ISink = 20 mA) |
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VOL |
± |
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0.1 |
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0.4 |
± |
0.1 |
0.4 |
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(ISink = 200 mA, UC284XB, UC384XB) |
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± |
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1.6 |
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2.2 |
± |
1.6 |
2.2 |
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(ISink = 200 mA, UC384XBV) |
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± |
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± |
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± |
± |
1.6 |
2.3 |
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High State |
(ISource = 20 mA, UC284XB, UC384XB) |
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VOH |
13 |
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13.5 |
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± |
13 |
13.5 |
± |
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(ISource = 20 mA, UC384XBV) |
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± |
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± |
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± |
12.9 |
± |
± |
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(ISource = 200 mA) |
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12 |
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13.4 |
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± |
12 |
13.4 |
± |
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Output Voltage with UVLO Activated |
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VOL(UVLO) |
± |
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0.1 |
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1.1 |
± |
0.1 |
1.1 |
V |
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VCC = 6.0 V, ISink = 1.0 mA |
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Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C) |
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tr |
± |
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50 |
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150 |
± |
50 |
150 |
ns |
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Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C) |
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tf |
± |
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50 |
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150 |
± |
50 |
150 |
ns |
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UNDERVOLTAGE LOCKOUT SECTION |
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Startup Threshold |
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Vth |
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V |
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UCX844B, BV |
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15 |
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16 |
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17 |
14.5 |
16 |
17.5 |
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UCX845B, BV |
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7.8 |
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8.4 |
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9.0 |
7.8 |
8.4 |
9.0 |
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Minimum Operating Voltage After Turn±On |
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VCC(min) |
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V |
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UCX844B, BV |
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9.0 |
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10 |
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11 |
8.5 |
10 |
11.5 |
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UCX845B, BV |
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7.0 |
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7.6 |
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8.2 |
7.0 |
7.6 |
8.2 |
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NOTES: 2. Adjust VCC above the Startup threshold before setting to 15 V. |
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3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. |
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Tlow = 0°C for UC3844B, UC3845B |
Thigh = + 70°C for UC3844B, UC3845B |
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= ± 25°C for UC2844B, UC2845B |
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= + 85°C for UC2844B, UC2845B |
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= ± 40°C for UC3844BV, UC3845BV |
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= +105°C for UC3844BV, UC3845BV |
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4. This parameter is measured at the latch trip point with VFB = 0 V.
5. Comparator gain is defined as: AV = |
DV Output Compensation |
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DV Current Sense Input |
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MOTOROLA ANALOG IC DEVICE DATA |
3 |
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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.)
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UC284XB |
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UC384XB, XBV |
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Characteristic |
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Symbol |
Min |
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Typ |
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Max |
Min |
Typ |
Max |
Unit |
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PWM SECTION |
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Duty Cycle |
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% |
Maximum (UC284XB, UC384XB) |
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DC(max) |
47 |
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48 |
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50 |
47 |
48 |
50 |
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(UC384XBV) |
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± |
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± |
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± |
46 |
48 |
50 |
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Minimum |
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DC(min) |
± |
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± |
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0 |
± |
± |
0 |
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TOTAL DEVICE |
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Power Supply Current |
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ICC |
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mA |
Startup (VCC = 6.5 V for UCX845B, |
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± |
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0.3 |
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0.5 |
± |
0.3 |
0.5 |
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14 V for UCX844B, BV) |
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Operating (Note 2) |
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± |
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12 |
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17 |
± |
12 |
17 |
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Power Supply Zener Voltage (ICC = 25 mA) |
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VZ |
30 |
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36 |
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± |
30 |
36 |
± |
V |
NOTES: 2. Adjust VCC above the Startup threshold before setting to 15 V. |
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3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. |
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Tlow = 0°C for UC3844B, UC3845B |
Thigh = + 70°C for UC3844B, UC3845B |
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= ± 25°C for UC2844B, UC2845B |
= + 85°C for UC2844B, UC2845B |
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= ± 40°C for UC3844BV, UC3845BV |
= +105°C for UC3844BV, UC3845BV |
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Figure 1. Timing Resistor versus Oscillator Frequency
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80 |
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VCC |
= 15 V |
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50 |
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° |
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Ω) |
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TA = 25 C |
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(k |
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RESISTOR |
20 |
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8.0 |
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, TIMING |
5.0 |
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T |
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R |
2.0 |
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NOTE: Output switches at |
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1/2 the oscillator frequency |
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0.8 |
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10 k |
20 k |
50 k |
100 k |
200 k |
500 k |
1.0 M |
fOSC, OSCILLATOR FREQUENCY (kHz)
Figure 2. Output Deadtime versus Oscillator Frequency
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75 |
1. |
CT = 10 nF |
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3 |
DEADTIME |
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70 |
2. |
CT = 5.0 nF |
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3. |
CT = 2.0 nF |
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2 |
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4. |
CT = 1.0 nF |
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4 |
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OUTPUT |
65 |
5. |
CT = 500 pF |
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6. |
CT = 200 pF |
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1 |
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7. |
CT = 100 pF |
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PERCENT |
60 |
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7 |
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55 |
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5 |
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% DT, |
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6 |
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50 |
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10 k |
20 k |
50 k |
100 k |
200 k |
500 k |
1.0 M |
fOSC, OSCILLATOR FREQUENCY (kHz)
Figure 3. Error Amp Small Signal
Transient Response
VCC = 15 V
2.55 V AV = ±1.0
TA = 25°C
2.5V
2.45V
0.5 μs/DIV
20 mV/DIV
3.0 V
2.5 V
2.0 V
Figure 4. Error Amp Large Signal
Transient Response
VCC = 15 V
AV = ±1.0
TA = 25°C
200 mV/DIV
1.0 μs/DIV
4 |
MOTOROLA ANALOG IC DEVICE DATA |
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UC3844B, 45B UC2844B, 45B |
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Figure 5. Error Amp Open Loop Gain and |
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Figure 6. Current Sense Input Threshold |
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Phase versus Frequency |
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0 |
(V) |
1.2 |
versus Error Amp Output Voltage |
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(dB) |
100 |
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VCC = 15 V |
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VCC = 15 V |
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GAIN |
80 |
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VO = 2.0 V to 4.0 V |
30 |
CURRENTSENSE INPUTTHRESHOLD |
1.0 |
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Gain |
RL = 100 k |
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VOLTAGE |
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° |
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60 |
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TA = 25 C |
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60 |
0.8 |
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TA = 25°C |
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40 |
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90 |
0.6 |
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LOOP |
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Phase |
TA = 125°C |
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20 |
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120 |
0.4 |
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OPEN |
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TA = ± 55°C |
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150 |
0.2 |
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, |
0 |
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VOL |
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(DEGREES)PHASEEXCESSφ, |
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A |
± 20 |
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180 |
, |
0 |
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th |
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10 |
100 |
1.0 k |
10 k |
100 k |
1.0 M |
10 M |
V |
0 |
2.0 |
4.0 |
6.0 |
8.0 |
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f, FREQUENCY (Hz) |
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VO, ERROR AMP OUTPUT VOLTAGE (VO) |
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Figure 7. Reference Voltage Change |
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(mV) |
0 |
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versus Source Current |
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VCC = 15 V |
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CHANGE |
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± 4.0 |
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VOLTAGE |
± 8.0 |
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± 12 |
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TA = ± 55°C |
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, REFERENCE |
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TA = 125°C |
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± 16 |
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± 20 |
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ref |
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TA = 25°C |
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V |
± 24 |
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0 |
20 |
40 |
60 |
80 |
100 |
120 |
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Iref, REFERENCE SOURCE CURRENT (mA) |
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(mA) |
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Figure 8. Reference Short Circuit Current |
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||||||
110 |
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versus Temperature |
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CURRENT |
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VCC = 15 V |
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RL ≤ 0.1 Ω |
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SHORT CIRCUIT |
90 |
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70 |
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, REFERENCE |
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50 |
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SC |
± 25 |
0 |
25 |
50 |
75 |
100 |
125 |
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± 55 |
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I |
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TA, AMBIENT TEMPERATURE (°C) |
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OUTPUT, CHANGEVOLTAGE mV/DIV)(2.0
O V
Figure 9. Reference Load Regulation
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
2.0 ms/DIV
OUTPUT, CHANGEVOLTAGE mV/DIV)(2.0
O V
Figure 10. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
2.0 ms/DIV
MOTOROLA ANALOG IC DEVICE DATA |
5 |
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