UC3844A High Performance
Current Mode Controller
lOutput Deadtime Adjustable from 50% to 70%
lCurrent Mode Operation to 500 kHz
lAutomatic Feed Forward Compensation
lLatching PWM for Cycle–By–Cycle Current Limiting
lInternally Trimmed Reference with Undervoltage Lockout
lHigh Current Totem Pole Output
lUndervoltage Lockout with Hysteresis
lLow Startup and Operating Current
CS SUFFIX
PLASTIC P ACKAGE
SOP-14
The UC3844A series of high performance
fixed frequency current mode controllers are
specifically designed for off–line and dc–to–dc
converter applications offering the designer a cost
effective solution with minimal external components.
This integrated circuit features 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%. This device is available in an 8–pin dual–in–
line plastic package as well as the 14–pin plastic sur-
face mount (SOP–14). The SOP–14 package has sepa-
rate power and ground pins for the totem pole output
stage. The UC3844A has UVLO thresholds of
16V (on) and 10V (off), Ideally suited for off-line
converters.
CD SUFFIX
PLASTIC P ACKAGE
8 DIP
PIN CONNECTIONSSIMPLIFIED BLOCK DIAGRAM
Pin numbers adjacent to terminals are for the D suffix 8-DIP package.
Pin numbers in parenthesis are for the S suffix SOP–14 package.
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, Thigh = +70°C.
4. This parameter is measured at the latch trip point with VFB = 0V.
5. Comparator gain is defined as: AV∆V Output Compensation
∆V Current Sense Input
D8 SUFFIX
PLASTIC P ACKAGE
8 SOP
4-24
UC3844A High Performance
Current Mode Controller
Total Power Supply and Zener Current (I CC +IZ)30mA
Output Current, Source or Sink (Note 1) IO1.0 A
Output Energy (Capacitive Load per Cycle) W 5 . 0 µJ
Current Sense and Voltage Feedback Inputs Vin -0.3 to +5.5 V
Error Amp Output Sink Current IO10 mA
Power Dissipation and Thermal Characteristics
CS, D8 Suffix, SOP-14, SOP-8 Package
Maximum Power Dissipation PD862 mW
Thermal Resistance, Junction to Air RθJA 145 oC/W
CD Suffix, 8-DIP Package
Maximum Power Dissipation PD1.25 W
Thermal Resistance, Junction to Air RθJA 100 oC/W
Operating Ambient T emperature Range T A0 to 70 oC
Operating Junction Temperature TJ150 oC
Storage T emperature Range TS-65 to 150 oC
Item Symbol Rating Unit
ABSOLUTE MAXIMUM RA TINGS
ELECTRICAL CHARACTERISTICS
Item Symbol Min Typ Max Unit
Reference Output Voltage (IO = 1.0mA, TJ = 25oC) VREF 4.9 5.0 5.1 V
Line Regulation (VCC = 12V to 25V) Regline --- 2.0 20 mV
Load Regulation (IO = 1.0mA to 20mA) Regload --- 3.0 25 mV
T emperature Stability TS--- 0.2 --- mV/oC
T otal Output Variation over Line, Load, T emp. V REF 4.82 --- 5.18 V
Output Noise Voltage (f = 10Hz to 10kHz, TJ = 25oC) Vn--- 50 --- µV
Long T erm Stability (TA = 125oC for 1000 Hours) S --- 5 .0 -- - mV
Output Short Circuit Current I S C - 3 0 - 8 5 -180 mA
VCC = 15V (Note 2), RT = 10k, CT = 3.3nF, TA = 0 to 70oC (Note 3) unless otherwise noted.
REFERENCE SECTION
Frequency fOSC V
TJ = 25oC475257
TA = 0 to 70oC 46 --- 60
Frequency Change with Voltage (VCC = 12V to 25V) ∆fOSC/∆V --- 0.2 1.0 %
Frequency Change with T emperature ∆fOSC/∆T --- 5.0 --- %
Oscillator Voltage Swing (Peak-to-Peak) VOSC --- 1.6 --- V
Discharge Current (VOSC = 2.0V) Idischg mA
TJ = 25oC --- 10.8 ---
OSCILLATOR SECTION
4-25
ELECTRICAL CHARACTERISTICS
Item Symbol Min Typ Max Unit
Voltage Feedback Input (VO = 2.5V) V FB 2.42 2.5 2.58 V
Input Bias Current (VFB = 2.7V) IIB --- -0.1 -2.0 µA
Open Loop Voltage Gain (VO = 2.0V to 4.0V) AVOL 65 90 --- dB
Unity Gain Bandwidth (TJ = 25oC) BW 0.7 1.0 --- MHz
Power Supply Rejection Ratio (VCC = 12V to 25V) PSRR 60 70 --- dB
Output Current mA
Sink (VO = 1.1V, VFB = 2.7V) ISink 2.0 12 ---
Source (VO = 5.0V, VFB = 2.3V) ISource -0.5 -1.0 ---
Output Voltage Swing V
High State (RL = 15k to GND, VFB = 2.3V) VOH 5.0 6.2 ---
Low State (RL = 15k to VREF, VFB = 2.3V) VOL --- 0.8 1.1
ERROR AMPLIFIER SECTION
UC3844A High Performance
Current Mode Controller
Current Sense Input Voltage Gain (Notes 4 & 5) AV2.85 3.0 3.15 V/V
Maximum Current Sense Input Threshold (Note 4) VTH 0.9 1.0 1.1 V
Power Supply Rejection Ratio (VCC = 12V to 25V) PSRR --- 70 --- dB
Input Bias Current IIB --- -2.0 -10 µA
Propagation Delay (Current Sense Input to Output) tPLH(in/out) --- 150 300 ns
CURRENT SENSE SECTION
Output Voltage V
Low State (I Sink = 20mA) VOL --- 0.1 0.4
(ISink = 200mA) --- 1.6 2.2
High State (I Sink = 20mA) VOH 13 13.5 ---
(ISink = 200mA) 1 2 13.4 ---
Output Voltage with UVLO Activated VOL(UVLO) V
(VCC = 6.0V , ISink = 1.0mA) --- 0.1 1.1
Output Voltage Rise Time (CL = 1.0nF , TJ = 25oC) tr--- 50 150 ns
Output Voltage Fall Time (CL = 1.0nF , TJ = 25oC) tf--- 50 150 ns
OUTPUT SECTION
Startup Threshold Vth 14.5 16 17.5 V
Minimum Operating Voltage After Turn-On VCC(min) 8.5 10 11.5 V
UNDERVOLTAGE LOCKOUT SECTION
Duty Cycle Max. DCmax 47 48 50 %
Min. DCmin --- --- 0
PWM SECTION
Power Supply Current (VCC = 14V) (Note 2) ICC mA
Startup -- - 0.17 0.3
Operating - - - 12 17
Power Supply Zener Voltage VZ30 36 --- V
TOTAL DEVICE
4-26
UC3844A High Performance
Current Mode Controller
FIGURE 1 - TIMING RESISTOR versus
OSCILLATOR FREQUENCY FIGURE 2 - OUTPUT DEADTIME versus
OSCILLATOR FREQUENCY
OSCILLATOR FREQUENCY (Hz)
TIMING RESISTOR (kΩ)
OSCILLATOR FREQUENCY (Hz)
PERCENT OUTPUT DEADTIME
FIGURE 3 - ERROR AMP SMALL SIGNAL
TRANSIENT RESPONSE FIGURE 4 - ERROR AMP LARGE SIGNAL
TRANSIENT RESPONSE
FIGURE 5 - ERROR AMP OPEN-LOOP GAIN
AND PHASE versus FREQUENCY
FREQUENCY (Hz)
OPEN-LOOP VOLTAGE GAIN (dB)
EXCESS PHASE (DEGREES)
FIGURE 6 - CURRENT SENSE INPUT THRESHOLD
versus ERROR AMP OUTPUT VOLTAGE
ERROR AMP OUTPUT VOLTAGE (V)
CURRENT SENSE INPUT
THRESHOLD (V)
4-27
UC3844A High Performance
Current Mode Controller
FIGURE 8 - REFERENCE SHORT CIRCUIT CURRENT
versus TEMPERATURE
AMBIENT TEMPERATURE (oC)
REFERENCE SHORT CIRCUIT
CURRENT (mA)
FIGURE 7 - REFERENCE VOLTAGE CHANGE
versus SOURCE CURRENT
REFERENCE SOURCE CURRENT (mA)
REFERENCE VOLTAGE CHANGE (mV)
FIGURE 9 - REFERENCE LOAD REGULATION
2.0 mS/DIV
OUTPUT VOLTAGE CHANGE (2.0mV/DIV)
FIGURE 10 - REFERENCE LINE REGULATION
2.0 mS/DIV
OUTPUT VOLTAGE CHANGE (2.0mV/DIV)
FIGURE 11 - OUTPUT SATURATION VOLTAGE
versus LOAD CURRENT
OUTPUT LOAD CURRENT (mA)
OUTPUT SATURATION VOLTAGE (V)
FIGURE 12 - OUTPUT WAVEFORM
4-28
UC3844A High Performance
Current Mode Controller
FIGURE 14 - SUPPLY CURRENT versus
SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
FIGURE 13 - OUTPUT CROSS CONDUCTION
SUPPLY CURRENT OUTPUT VOLTAGE
4-29
