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HIGH PERFORMANCE CURRENT MODE CONTROLLERS

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Niveau: Supérieur, Doctorat, Bac+8
Device Operating Temperature Range Package HIGH PERFORMANCE CURRENT MODE CONTROLLERS ORDERING INFORMATION UC3844D UC3845D TA = 0° to +70°C TA = – 25° to +85°C SO–14 SO–14 PIN CONNECTIONS Order this document by UC3844/D D SUFFIX PLASTIC PACKAGE CASE 751A (SO–14) N SUFFIX PLASTIC PACKAGE CASE 626 1 8 1 14 (Top View) Vref (Top View) Compensation Voltage Feedback Current Sense RT/CT Vref VCC Output Gnd 1 2 3 4 5 6 7 8 Compensation NC Voltage Feedback NC Current Sense NC RT/CT NC VCC VC Output Gnd Power Ground 1 2 3 4 5 6 7 9 8 10 11 12 13 14 UC3844N UC3845N Plastic Plastic UC2844D UC2845D SO–14 SO–14 UC2844N UC2845N Plastic Plastic 1MOTOROLA ANALOG IC DEVICE DATA 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.

  • input bias

  • current sense

  • maintain junction temperature

  • pwm section

  • operating ambient

  • so–14 so–14

  • output voltage

  • undervoltage lockout

  • reference short


Subjects

Informations

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Language English

Order this document by UC3844/D
HIGH PERFORMANCE
The UC3844, UC3845 series are high performance fixed frequency
CURRENT MODEcurrent mode controllers. They are specifically designed for Off–Line and
dc–to–dc converter applications offering the designer a cost effective CONTROLLERS
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.
N SUFFIX
Also included are protective features consisting of input and reference PLASTIC PACKAGE
undervoltage lockouts each with hysteresis, cycle–by–cycle current limiting, CASE 626
a latch for single pulse metering, and a flip–flop which blanks the output off 8
every other oscillator cycle, allowing output deadtimes to be programmed for
1
50% to 70%. D SUFFIX
These devices are available in an 8–pin dual–in–line plastic package as PLASTIC PACKAGE
14CASE 751Awell as the 14–pin plastic surface mount (SO–14). The SO–14 package has
(SO–14) 1separate 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).
PIN CONNECTIONS
• Current Mode Operation to 500 kHz Output Switching Frequency
Compensation 1 8 V• Output Deadtime Adjustable from 50% to 70% ref
• Automatic Feed Forward Compensation Voltage Feedback 2 7 VCC
• Latching PWM for Cycle–By–Cycle Current Limiting 3 6Current Sense Output
• Internally Trimmed Reference with Undervoltage Lockout 45R /C GndT T
• High Current Totem Pole Output
(Top View)• Input Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
1 14Compensation Vref• Direct Interface with Motorola SENSEFET Products
2 13NC NC
3 12Voltage Feedback VCC
4 11 VNC C
5 10Current Sense Output
6 9NC GndSimplified Block Diagram
R /C Power Ground7 8T TV 7(12)CC
(Top View)V VCCref 5.0V
Undervoltage8(14) Reference
Lockout ORDERING INFORMATIONR
V Operatingref VCR Undervoltage Device Temperature Range Package7(11)
Lockout
UC3844D SO–14R C OutputT T
Oscillator Flip 6(10)4(7) UC3845D SO–14Flop
T = 0° to +70°CA&Voltage PWR GND UC3844N Plastic
LatchingFeedback 5(8)+
PWM– UC3845N Plastic2(3) Current
Error Sense UC2844D SO–14Amplifier 3(5)
1(1)
UC2845D SO–14Output
T = – 25° to +85°CAComp. Gnd 5(9) UC2844N Plastic
Pin numbers in parenthesis are for the D suffix SO–14 package. UC2845N Plastic
 Motorola, Inc. 1996 Rev 1
1MOTOROLA ANALOG IC DEVICE DATA

UC3844, 45 UC2844, 45
MAXIMUM RATINGS
Rating Symbol Value Unit
Total Power Supply and Zener Current (I + I ) 30 mACC Z
Output Current, Source or Sink (Note 1) I 1.0 AO
Output Energy (Capacitive Load per Cycle) W 5.0 J
Current Sense and Voltage Feedback Inputs V – 0.3 to + 5.5 Vin
Error Amp Output Sink Current I 10 mAO
Power Dissipation and Thermal Characteristics
D Suffix, Plastic Package, Case 751A
Maximum Power Dissipation @ T = 25°C P 862 mWA D
Thermal Resistance Junction–to–Air R 145 °C/WJA
N Suffix, Plastic Package, Case 626 = 25°C P 1.25 WA D R 100 °C/WJA
Operating Junction Temperature T + 150 °CJ
Operating Ambient T T °CA
UC3844, UC3845 0 to + 70
UC2844, UC2845 – 25 to + 85
Storage Temperature Range T – 65 to + 150 °Cstg
ELECTRICAL CHARACTERISTICS (V = 15 V, [Note 2], R = 10 k, C = 3.3 nF, T = T to T [Note 3], CC T T A low high
unless otherwise noted.)
UC284X UC384X
Characteristics Symbol Min Typ Max Min Typ Max Unit
REFERENCE SECTION
Reference Output Voltage (I = 1.0 mA, T = 25°C) V 4.95 5.0 5.05 4.9 5.0 5.1 VO J ref
Line Regulation (V = 12 V to 25 V) Reg – 2.0 20 – 2.0 20 mVCC line
Load Regulation (I = 1.0 mA to 20 mA) Reg – 3.0 25 – 3.0 25 mVO load
Temperature Stability T – 0.2 – – 0.2 – mV/°CS
Total Output Variation over Line, Load, Temperature V 4.9 – 5.1 4.82 – 5.18 Vref
Output Noise Voltage (f = 10 Hz to kHz, T = 25°C) V – 50 – – 50 – VJ n
Long Term Stability (T = 125°C for 1000 Hours) S – 5.0 – – 5.0 – mVA
Output Short Circuit Current I – 30 – 85 – 180 – 30 – 85 – 180 mASC
OSCILLATOR SECTION
Frequency f kHzosc
T = 25°C 47 52 57 47 52 57J
T = T to T 46 – 60 46 – 60A low high
Frequency Change with Voltage (V = 12 V to 25 V) f – 0.2 1.0 – 0.2 1.0 %CC osc/ V
Frequency Change with Temperature f – 5.0 – – 5.0 – %osc/ T
T = T to TA low high
Oscillator Voltage Swing (Peak–to–Peak) V – 1.6 – – 1.6 – Vosc
Discharge Current (V = 2.0 V, T = 25°C) I – 10.8 – – 10.8 – mAosc J dischg
NOTES: 1. Maximum Package power dissipation limits must be observed.
2. Adjust V above the Startup threshold before setting to 15 V.CC
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
T = –20°C for UC3844, UC3845 T = +70°C for UC3844, UC3845low high
T = –25°C for UC2844, UC2845 T = +85°C for UC2844, UC2845low high
2 MOTOROLA ANALOG IC DEVICE DATA
mDDmqDDqUC3844, 45 UC2844, 45
ELECTRICAL CHARACTERISTICS (V = 15 V, [Note 2], R = 10 k, C = 3.3 nF, T = T to T [Note 3], CC T T A low high
unless otherwise noted,)
UC284X UC384X
Characteristics Symbol Min Typ Max Min Typ Max Unit
ERROR AMPLIFIER SECTION
Voltage Feedback Input (V = 2.5 V) V 2.45 2.5 2.55 2.42 2.5 2.58 VO FB
Input Bias Current (V = 2.7 V) I – –0.1 –1.0 – –0.1 –2.0 AFB IB
Open Loop Voltage Gain (V = 2.0 V to 4.0 V) A 65 90 – 65 90 – dBO VOL
Unity Gain Bandwidth (T = 25°C) BW 0.7 1.0 – 0.7 1.0 – MHzJ
Power Supply Rejection Ratio (V = 12 V to 25 V) PSRR 60 70 – 60 70 – dBCC
Output Current mA
Sink (V = 1.1 V, V = 2.7 V) I 2.0 12 – 2.0 12 –O FB Sink
Source (V = 5.0 V, V = 2.3 V) I –0.5 –1.0 – –0.5 –1.0 –O FB Source
Output Voltage Swing V
High State (R = 15 k to ground, V = 2.3 V) V 5.0 6.2 – 5.0 6.2 –L FB OH
Low State (R = 15 k to V , V = 2.7 V) V – 0.8 1.1 – 0.8 1.1L ref FB OL
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5) A 2.85 3.0 3.15 2.85 3.0 3.15 V/VV
Maximum Current Sense Input Threshold (Note 4) V 0.9 1.0 1.1 0.9 1.0 1.1 Vth
Power Supply Rejection Ratio PSRR dB
V = 12 V to 25 V (Note 4) – 70 – – 70 –CC
Input Bias Current I – –2.0 –10 – –2.0 –10 AIB
Propagation Delay (Current Sense Input to Output) t – 150 300 – 150 300 nsPLH(IN/OUT)
OUTPUT SECTION
Output Voltage V
Low State (I = 20 mA) V – 0.1 0.4 – 0.1 0.4Sink OL
(I = 200 mA) – 1.6 2.2 – 1.6 2.2Sink
High State (I = 20 mA) V 12 13.5 – 13 13.5 –Sink OH
(I = 200 mA) 12 13.4 – 12 13.4 –Sink
Output Voltage with UVLO Activated V VOL(UVLO)
V = 6.0 V, I = 1.0 mA – 0.1 1.1 – 0.1 1.1CC Sink
Output Voltage Rise Time (C = 1.0 nF, T = 25°C) t – 50 150 – 50 150 nsL J roltage Fall Time (C, T = 25°C) t – 50 150 – 50 150 nsL J f
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold V Vth
UCX844 15 16 17 14.5 16 17.5
UCX845 7.8 8.4 9.0 7.8 8.4 9.0
Minimum Operating Voltage After Turn–On V VCC(min)
UCX844 9.0 10 11 8.5 10 11.5
UCX845 7.0 7.6 8.2 7.0 7.6 8.2
PWM SECTION
Duty Cycle %
Maximum DC 46 48 50 47 48 50max
Minimum DC – – 0 – – 0min
TOTAL DEVICE
Power Supply Current (Note 2) I mACC
Startup:
(V = 6.5 V for UCX845A, – 0.5 1.0 – 0.5 1.0CC
(V 14 V for UCX844) Operating – 12 17 – 12 17CC
Power Supply Zener Voltage (I = 25 mA) V 30 36 – 30 36 – VCC Z
NOTES: 2. Adjust V above the Startup threshold before setting to 15 V.CC
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
T = –20°C for UC3844, UC3845 T = +70°C for UC3844, UC3845low high
T = –25°C for UC2844, UC2845 T = +85°C for UC2844, UC2845low high
4. This parameter is measured at the latch trip point with V = 0 V.FB
V Output Compensation
5. Comparator gain is defined as: AV
V Current Sense Input
3MOTOROLA ANALOG IC DEVICE DATA
DmDmUC3844, 45 UC2844, 45
Figure 1. Timing Resistor versus Figure 2. Output Deadtime versus
Oscillator Frequency Oscillator Frequency
100 75
V = 15 VCC
T = 25°CA 1.0 nF50
70
2.0 nF
20
5.0 nF
65
C = 10 nFT
10
605.0
2.0 55 100 pFNOTE: Output switches
at one–half the oscillator
200 pFfrequency. 500 pF
1.0 50
10 k 20 k 50 k 100 k 200 k 500 k 1.0 M 10 k 20 k 50 k 100 k 200 k 500 k 1.0 M
f , OSCILLATOR FREQUENCY (Hz) f , OSCILLATOR FREQUENCY (Hz)osc osc
Figure 3. Error Amp Small Signal Figure 4. Error Amp Large Signal
Transient Response Transient Response
V = 15 V V = 15 VCC CC
A = –1.0 A = –1.0V V2.55 V 3.0 V
T = 25°C T = 25°CA A
2.5 V 2.5 V
2.45 V 2.0 V
0.5 s/DIV 1.0 s/DIV
Figure 5. Error Amp Open Loop Gain and Figure 6. Current Sense Input Threshold
Phase versus Frequency versus Error Amp Output Voltage
100 1.20
V = 15 VCC V = 15 VCC
V = 2.0 V to 4.0 VO
80 30 1.0R = 100 KLGain
T = 25°CA
60 60 0.8
T = 25°CA
0.640 90
T = 125°CPhase A
20 0.4120 T = –55°CA
0 0.2150
180–20 0
10 100 1.0 k 10 k 100 k 1.0 M 10 M 0 2.0 4.0 6.0 8.0
f, FREQUENCY (Hz) V , ERROR AMP OUTPUT VOLTAGE (V)O
4 MOTOROLA ANALOG IC DEVICE DATA
mWfm
A , OPEN LOOP VOLTAGE GAIN (dB)
R , TIMING RESISTOR (k )
VOL
T
20 mV/DIV
, EXCESS PHASE (DEGREES)
% DT, PERCENT OUTPUT DEADTIME
, CURRENT SENSE INPUT THRESHOLD (V)
V
th
200 mV/DIVO
O
UC3844, 45 UC2844, 45
Figure 7. Reference Voltage Change Figure 8. Reference Short Circuit Current
versus Source Current versus Temperature
0 110
V = 15 VCC
V = 15 VCC–4.0
R ≤ 0.1 L
–8.0 90
–12
70–16 T = 125°CA
T = –55°CA
–20 T = 25°CA
–24 50
0 20 40 60 80 100 120 –55 –25 0 25 50 75 100 125
I , REFERENCE SOURCE CURRENT (mA) T , AMBIENT TEMPERATURE (°C)ref A
Figure 9. Reference Load Regulation Figure 10. Reference Line Regulation
V = 15 VCC V = 12 V to 25 VCC
I = 1.0 mA to 20 mAO °CT = 25A
T = 25°CA
2.0 ms/DIV 2.0 ms/DIV
Figure 11. Output Saturation Voltage
versus Load Current Figure 12. Output Waveform
0
Source Saturation V = 15 VV CCCC
(Load to Ground) 80 s Pulsed Load V = 15 VCC
–1.0 120 Hz RateT = 25°C C = 1.0 nFA L90%
T = 25°CA
–2.0
T = –55°CA
3.0
T = –55°CA
2.0 T = 25°CA
10%
1.0 Sink Saturation
Gnd(Load to V )CC
0
50 ns/DIV0 200 400 600 800
I , OUTPUT LOAD CURRENT (mA)O
5MOTOROLA ANALOG IC DEVICE DATA
mDDWD
V , OUTPUT SATURATION VOLTAGE (V)
sat V , REFERENCE VOLTAGE CHANGE (mV)
ref
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
I , REFERENCE SHORT CIRCUIT CURRENT (mA)
SC
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)UC3844, 45 UC2844, 45
Figure 14. Supply Current versus
Figure 13. Output Cross Conduction Supply Voltage
25
V = 30 VCC
C = 15 pFL
T = 25°CA 20
15
10 R = 10 kT
C = 3.3 nFT
V = 0 VFB
5 I = 0 VSense
T = 25°CA
0
0 10203040100 ns/DIV
V , SUPPLY VOLTAGE (V)CC
PIN FUNCTION DESCRIPTION
Pin
FunctionFi DiDescriptioni8–Pin 14–Pin
1 1 Compensation This pin is Error Amplifier output and is made available for loop compensation.
2 3 Voltage This is the inverting input of the Error Amplifier. It is normally connected to the switching power
Feedback supply output through a resistor divider.
3 5 Current Sense A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
4 7 R /C The Oscillator frequency and maximum Output duty cycle are programmed by connectingT T
resistor R to V and capacitor C to ground. Operation to 1.0 MHz is possible.T ref T
5 – Gnd This pin is combined control circuitry and power ground (8–pin package only).
6 10 Output This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced
and sunk by this pin. The output switches at one–half the oscillator frequency.
7 12 V This pin is the positive supply of the control IC.CC
8 14 V This is the reference output. It provides charging current for capacitor C through resistor R .ref T T
– 8 Power Ground This pin is a separate power ground return (14–pin package only) that is connected back to the
power source. It is used to reduce the effects of switching transient noise on the control circuitry.
– 11 V The Output high state (V ) is set by the voltage applied to this pin (14–pin package only). WithC OH
a separate power source connection, it can reduce the effects of switching transient noise on the
control circuitry.
– 9 Gnd This pin is the control circuitry ground return (14–pin package only) and is connected to back to
the power source ground.
– 2,4,6,13 NC No connection (14–pin package only). These pins are not internally connected.
6 MOTOROLA ANALOG IC DEVICE DATA
I , SUPPLY CURRENT V , OUTPUT VOLTAGE
CC O
100 mA/DIV 20 V/DIV
I , SUPPLY CURRENT (mA)
CC
UCX845
UCX844UC3844, 45 UC2844, 45
OPERATING DESCRIPTION
The UC3844, UC3845 series are high performance, fixed Amp minimum feedback resistance is limited by the
frequency, current mode controllers. They are specifically amplifier’s source current (0.5 mA) and the required output
designed for Off–Line and dc–to–dc converter applications voltage (V ) to reach the comparator’s 1.0 V clamp level:OH
offering the designer a cost effective solution with minimal
external components. A representative block diagram is 3.0 (1.0 V) + 1.4 V
R ≈ = 8800 Wf(min)shown in Figure 15. 0.5 mA
Oscillator
Current Sense Comparator and PWM Latch
The oscillator frequency is programmed by the values The UC3844, UC3845 operate as a current mode
selected for the timing components R and C . Capacitor CT T T controller, whereby output switch conduction is initiated by
is charged from the 5.0 V reference through resistor R toT the oscillator and terminated when the peak inductor current
approximately 2.8 V and discharged to 1.2 V by an internal
reaches the threshold level established by the Error Amplifier
current sink. During the discharge of C , the oscillatorT Output/Compensation (Pin1). Thus the error signal controls
generates an internal blanking pulse that holds the center
the inductor current on a cycle–by–cycle basis. The current
input of the NOR gate high. This causes the Output to be in a
Sense Comparator PWM Latch configuration used ensures
low state, thus producing a controlled amount of output
that only a single pulse appears at the Output during any
deadtime. An internal flip–flop has been incorporated in the
given oscillator cycle. The inductor current is converted to a
UCX844/5 which blanks the output off every other clock cycle voltage by inserting the ground referenced sense resistor RSby holding one of the inputs of the NOR gate high. This in
in series with the source of output switch Q1. This voltage is
combination with the C discharge period yields outputT monitored by the Current Sense Input (Pin 3) and compared
deadtimes programmable from 50% to 70%. Figure 1 shows
a level derived from the Error Amp Output. The peak inductor
R versus Oscillator Frequency and figure 2, OutputT current under normal operating conditions is controlled by the
Deadtime versus Frequency, both for given values of C .T voltage at pin 1 where:
Note that many values of R and C will give the sameT T
oscillator frequency but only one combination will yield a
V – 1.4 V(Pin 1)specific output deadtime at a given frequency. I =pk
3 RSIn many noise sensitive applications it may be desirable to
frequency–lock the converter to an external system clock.
This can be accomplished by applying a clock signal to the Abnormal operating conditions occur when the power
circuit shown in Figure 17. For reliable locking, the supply output is overloaded or if output voltage sensing is
free–running oscillator frequency should be set about 10% lost. Under these conditions, the Current Sense Comparator
less than the clock frequency. A method for multi unit threshold will be internally clamped to 1.0 V. Therefore the
synchronization is shown in Figure 18. By tailoring the clock maximum peak switch current is:
waveform, accurate Output duty cycle clamping can be
1.0 Vachieved to realize output deadtimes of greater than 70% I =pk(max) RS
Error Amplifier
A fully compensated Error Amplifier with access to the When designing a high power switching regulator it
inverting input and output is provided. It features a typical dc becomes desirable to reduce the internal clamp voltage in
voltage gain of 90 dB, and a unity gain bandwidth of 1.0 MHz order to keep the power dissipation of R to a reasonableS
with 57 degrees of phase margin (Figure 5). The noninverting level. A simple method to adjust this voltage is shown in
input is internally biased at 2.5 V and is not pinned out. The Figure 19. The two external diodes are used to compensate
converter output voltage is typically divided down and the internal diodes yielding a constant clamp voltage over
monitored by the inverting input. The maximum input bias temperature. Erratic operation due to noise pickup can result
if there is an excessive reduction of the I clampcurrent is –2.0 m A which can cause an output voltage error pk(max)
voltage.that is equal to the product of the input bias current and the
equivalent input divider source resistance. A narrow spike on the leading edge of the current
The Error Amp Output (Pin 1) is provide for external loop waveform can usually be observed and may cause the power
compensation (Figure 28). The output voltage is offset by two supply to exhibit an instability when the output is lightly
diode drops (≈ 1.4 V) and divided by three before it connects loaded. This spike is due to the power transformer
to the inverting input of the Current Sense Comparator. This interwinding capacitance and output rectifier recovery time.
guarantees that no drive pulses appear at the Output (Pin 6) The addition of an RC filter on the Current Sense Input with a
when Pin 1 is at its lowest state (V ). This occurs when the time constant that approximates the spike duration willOL
usually eliminate the instability; refer to Figure 23.power supply is operating and the load is removed, or at the
beginning of a soft–start interval (Figures 20, 21). The Error
7MOTOROLA ANALOG IC DEVICE DATAUC3844, 45 UC2844, 45
Figure 15. Representative Block Diagram
VV inCC
VCC 7(12)
36V
V +ref Reference
Regulator –8(14) V +CCR Internal UVLO
–Bias2.5V + VC
–R RT + 7(11)Vref3.6V
– UVLO
Q1Output
Oscillator
6(10)4(7) T Q
+CT 1.0mA
Power GroundS
+ Q
– 5(8)RVoltage Feedback – PWM2R +
Input Latch2(3)
Error R Current Sense Input1.0VOutput Amplifier
Compensation Current Sense 3(5)
1(1) RComparator S
Gnd 5(9) + Sink Only
=
Positive True Logic–
Pin numbers in parenthesis are for the D suffix SO–14 package.
Figure 16. Timing Diagram
Capacitor CT
Latch
‘‘Set’’ Input
Output/
Compensation
Current Sense
Input
Latch
‘‘Reset’’ Input
Output
Large R /Small C Small R /Large CT T T T
8 MOTOROLA ANALOG IC DEVICE DATA