The MC44602 is an enhanced high performance fixed frequency current
mode controller that is specifically designed for off–line and high voltage
dc–to–dc converter applications. This device has the unique ability of
changing operating modes if the converter output is overloaded or shorted,
offering the designer additional protection for increased system reliability.
The MC44602 has several distinguishing features when compared to
conventional current mode controllers. These features consist of a foldback
amplifier for overload detection, valid load and demag comparators with a
fault latch for short circuit detection, thermal shutdown, and separate high
current source and sink outputs that are ideally suited for driving a high
voltage bipolar power transistor, such as the MJE18002, MJE18004, or
MJE18006.
Standard features include an oscillator with a sync input, a temperature
compensated reference, high gain error amplifier, and a current sensing
comparator. Protective features consist 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%. This device is manufactured in a 16 pin dual–in–line heat tab package
for improved thermal conduction.
• Separate High Current Source and Sink Outputs Ideally Suited for
Driving Bipolar Power Transistors: 1.0 A Source, 1.5 A Sink
• Unique Overload and Short Circuit Protection
• Thermal Protection
• Oscillator with Sync Input
• 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
• Input and Reference Undervoltage Lockouts with Hysteresis
• Low Startup and Operating Current
Simplified Block Diagram
V
V
ref
16
Sync Input
RT/C
T
Compensation
Voltage Feedback–Input
7
8
1
3
V
ref
Undervoltage
Lockout
Oscillator
Error
Amplifier
Foldback
Amplifier
5.0V
Reference
Flip Flop
and
Latching
PWM
Gnd9
CC
Undervoltage
Lockout
Short Circuit
Detection
Thermal
V
CC
15
Load Detect Input
2
V
C
14
Source Output
11
Sink Output
10
Sink Ground
4, 5, 12, 13
Current Sense Input
6
Order this document by MC44602/D
HIGH PERFORMANCE
CURRENT MODE
CONTROLLER
SEMICONDUCTOR
TECHNICAL DATA
16
1
P2 SUFFIX
PLASTIC PACKAGE
CASE 648C
DIP (12 + 2 + 2)
PIN CONNECTIONS
RT/C
T
1
2
3
4
5
6
7
8
(Top View)
Compensation
Load Detect Input
Voltage Feedback Input
Sink Gnd
Current Sense Input
Sync Input
ORDERING INFORMATION
Operating
Device
MC44602TA = –25 to 85°CDIP (12 + 2 + 2)
Temperature Range
16
V
ref
15
V
CC
14
V
C
13
Sink Gnd
12
11
Source Output
10
Sink Output
9
Gnd
Package
MOTOROLA ANALOG IC DEVICE DATA
Motorola, Inc. 1996Rev 0
1
Page 2
MC44602
MAXIMUM RATINGS
RatingSymbolValueUnit
Total Power Supply and Zener Current(ICC + IZ)30mA
Sink Ground Voltage
with Respect to Gnd (Pin 9)
Output Supply Voltage
with Respect to Sink Gnd (Pins 4, 5, 12, 13)
Output Current (Note 1)
Source
Sink
Output Energy (Capacitive Load per Cycle)W5.0µJ
Current Sense and Voltage Feedback InputsV
Sync Input
High State Voltage
Low State Reverse Current
Load Detect Input CurrentI
Error Amplifier Output Sink CurrentIEA
Power Dissipation and Thermal Characteristics
NOTE: 1.Maximum package power dissipation limits must be observed.
V
Sink(neg)
V
C
I
O(Source)
I
O(Sink)
in
V
IH
I
IL
in
(Sink)
P
D
R
θJA
R
θJC
J
A
–5.0V
20V
1.0
1.5
–0.3 to 5.5V
5.5
–20
–20 to +10mA
10mA
2.5
80
15
150°C
–25 to +85°C
A
V
mA
W
°C/W
°C/W
ELECTRICAL CHARACTERISTICS(V
values TA = –25°C to +85°C [Note 3] unless otherwise noted.)
Characteristic
ERROR AMPLIFIER SECTION
Voltage Feedback Input (VO = 2.5V)V
Input Bias Current (VFB = 2.5 V)I
Open Loop Voltage Gain (VO = 2.0 V to 4.0 V)A
Unity Gain Bandwidth
TJ = 25°C
TA = –25 to +85°C
Power Supply Rejection Ratio (VCC = 10 V to 16 V)PSRR6570–dB
Output Current
Sink (VO = 1.5 V, VFB = 2.7 V)
Sink TJ = 25°C
Sink TA = –25 to +85°C
Source (VO = 5.0 V, VFB = 2.3 V)
Source TJ = 25°C
Source TA = –25 to +85°C
Output Voltage Swing
High State (I
Low State (I
NOTES: 2. Adjust VCC above the startup threshold before setting to 12V.
O(Source)
O(Sink)
3.Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
= 0.5 mA, VFB = 2.3 V)
= 0.33 mA, VFB = 2.7 V)
and VC = 12 V [Note 2], RT = 10k, CT = 1.0 nF, for typical values TA = 25°C, for min/max
CC
SymbolMinTypMaxUnit
FB
IB
VOL
BW
I
Sink
I
Source
V
OH
V
OL
2.452.52.65V
––0.6–2.0µA
6590–dB
1.0
0.8
–
1.5
–
–2.0
6.0
–
1.4
–
5.0
–
–1.1
–
7.0
1.0
1.8
2.0
–
10
–
–0.2
–
1.1
MHz
mA
V
2
MOTOROLA ANALOG IC DEVICE DATA
Page 3
MC44602
ELECTRICAL CHARACTERISTICS(V
and VC = 12 V [Note 2], RT = 10k, CT = 1.0 nF, for typical values TA = 25°C, for min/max
CC
values TA = –25°C to +85°C [Note 3] unless otherwise noted.)
Characteristic
SymbolMinTypMaxUnit
OSCILLATOR SECTION
Frequency
TJ = 25°C
TA = –25°C to +85°C
Frequency Change with Voltage (VCC = 12 V to 18 V)∆f
Frequency Change with Temperature∆f
Oscillator Voltage Swing (Peak–to–Peak)V
Discharge Current (V
TJ = 25°C
OSC
= 3.0 V)
TA = –25°C to +85°C
f
OSC
/∆V–0.10.2%/V
OSC
/∆T–0.05–%/°C
OSC
OSC(pp)
I
dischg
168
160
180
–
192
200
1.31.6–V
6.5
6.0
10
–
14
13.5
Sync Input Threshold Voltage
High State
Low State
Sync Input Resistance
TJ = 25°C
TA = –25°C to +85°C
V
IH
V
IL
R
in
2.5
1.0
6.5
6.0
2.8
1.3
10
3.2
1.7
13.5
–
18
REFERENCE SECTION
Reference Output Voltage (IO = 1.0 mA)V
Line Regulation (VCC = 12 V to 18 V)Reg
Load Regulation (IO = 1.0 mA to 20 mA)Reg
T emperature StabilityT
Total Output Variation over Line, Load and TemperatureV
Output Noise Voltage (f = 10 Hz to 10 kHz, TJ = 25°C)V
ref
line
load
S
ref
n
4.75.05.3V
–1.010mV
–3.015mV
–0.2–mV/°C
4.65–5.35V
–50–µV
Long Term Stability (TA = 125°C for 1000 Hours)S–5.0–mV
Output Short Circuit Current
TJ = 25°C
TA = –25°C to +85°C
I
SC
–
–70
–130
–
–
–180
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)
TJ = 25°C
TA = –25°C to +85°C
Maximum Current Sense Input Threshold (Note 4)V
Input Bias CurrentI
Propagation Delay (Current Sense Input to Sink Output)t
A
V
th
IB
PLH(in/out)
2.85
2.7
3.0
–
3.2
3.15
0.91.01.1V
––4.0–10µA
–100150ns
UNDERVOLTAGE LOCKOUT SECTIONS
Startup Threshold (VCC Increasing) V
Minimum Operating Voltage After Turn–On (VCC Decreasing) V
Reference Undervoltage Threshold (V
NOTES: 2.Adjust VCC above the startup threshold before setting to 12V.
3.Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
4.This parameter is measured at the latch trip point with IFB = –5.0
5.Comparator gain is defined as AV =
Decreasing) V
ref
µA, refer to Figure 9.
∆V Compensation
∆V Current Sense Input
th
CC(min)
(UVLO)3.03.353.7V
ref
1314.115V
9.010.211V
kHz
mA
V
kΩ
mA
V/V
MOTOROLA ANALOG IC DEVICE DATA
3
Page 4
MC44602
Ä
ÄÄÄÄ
ÄÄÄÄ
ÄÄÄÄ
ELECTRICAL CHARACTERISTICS
(V
and VC = 12 V [Note 2], RT = 10k, CT = 1.0 nF, for typical values TA = 25°C, for min/max
CC
values TA = –25°C to +85°C [Note 3] unless otherwise noted.)
Characteristic
SymbolMinTypMaxUnit
OUTPUT SECTION
Output Voltage (TA = 25°C)
Low State (I
Low State (I
Low State (I
High State (I
High State (I
High State (I
Output Voltage with UVLO Activated (VCC = 6.0 V, I
Output Voltage Rise T ime (CL = 1.0 nF, TJ = 25°C)t
Output Voltage Fall T ime (CL = 1.0 nF, TJ = 25°C)t
RT = 10 k
CT = 1.0 nF
VFB = 0 V
Current Sense = 0 V
24
16
, SUPPLY CURRENT (mA)
8.0
CC
I
0
TA = 25
0
°
C
4.08.012162024
VCC, SUPPLY VOLTAGE (V)
µ
s Pulsed Load
–2.0
–2.5
, SINK OUTPUT SA TURATION VOLTAGE (V)
sat
V
–3.0
0
23
22
21
, ZENER VOLTAGE (V)
CC
20
V
19
–55
TJ = –55°C
Source Saturation
(Load to Ground)
150300450600750900
I
, OUTPUT SOURCE CURRENT (mA)
source
TJ = 25°C
Figure 20. Power Supply Zener V oltage
versus T emperature
ICC = 25 mA
–250255075125
TA, AMBIENT TEMPERATURE (°C)
100
MOTOROLA ANALOG IC DEVICE DATA
7
Page 8
MC44602
3.2
2.8
2.4
, VALID LOAD COMPARATOR THRESHOLD (V)
2.0
th(VL)
V
µ
1.4
1.2
Figure 21. Valid Load Comparator Threshold
versus T emperature
–55
–250255075125
°
TA, AMBIENT TEMPERATURE (
C)
Figure 23. Load Detect Input
Propagation Delay versus T emperature
VCC = 12 V
RT = 10 k
CT = 1.0 nF
VCC = 12 V
100
120
100
80
, DEMAG COMPARATOR THRESHOLD (mV)
60
th(Demag)
–55
V
14.5
14.3
Figure 22. Demag Comparator Threshold
versus T emperature
VCC = 12 V
–250255075125
TA, AMBIENT TEMPERATURE (
°
100
C)
Figure 24. Startup Threshold V oltage
versus T emperature
VCC Increasing
1.0
, LOAD DETECT PROPAGATION DELAY ( s)
0.8
–55
PLH(IN/OUT)
t
10.35
10.25
10.15
10.05
, MINIMUM OPERATING VOLTAGE (V)
CC(min)
V
9.95
–55
–250255075125
TA, AMBIENT TEMPERATURE (
°
100
C)
Figure 25. Minimum Operating V oltage
After Turn–On versus Temperature
VCC Decreasing
–250255075125100
TA, AMBIENT TEMPERATURE (
°
C)
14.1
13.9
, STARTUP THRESHOLD VOLTAGE (V)
th
V
13.7
–55
3.42
3.38
3.34
, REFERENCE UNDERVOL TAGE THRESHOLD (V)
3.30
–55
ref(UVLO)
V
–250255075125
TA, AMBIENT TEMPERATURE (
°
100
C)
Figure 26. Reference Undervoltage Threshold
versus T emperature
V
Decreasing
ref
–250255075125100
TA, AMBIENT TEMPERATURE (
°
C)
8
MOTOROLA ANALOG IC DEVICE DATA
Page 9
V
ref
16
Sync Input
R
T
C
T
Compensation
Voltage Feedback
Input
MC44602
Figure 27. Representative Block Diagram
V
CC
V
CC
+
R
R
2.5V
7
10k
Oscillator
8
1
2.5V
3
Amplifier
2.5V
Internal
Bias
Error
I
3.6V
Fault Latch
+
1.0 mA
Foldback
Amplifier
Demag
Comparator
Valid Load
Comparator
R
Q
S
2R
1.0V
Reference
Regulator
Reference
UVLO
ThermalRSQ
R
Current Sense
Comparator
V
UVLO
85mV
2.5V
TQ
R
PWM
Latch
CC
18k
20V
14V
+
Substrate
15
Load
Detect
Input
2
V
C
14
Source Output
11
Sink Output
10
Sink Ground
4, 5, 12, 13
Current Sense Input
6
V
in
V
out
Q1
R
S
Capacitor C
T
PWM Latch
“Set” Input
Toggle Flip Flop
Output
Q
Current Sense
Input
PWM Latch
“Set” Input
Source Output
Load Detect
85mV
Input
2.8V
1.2V
0V
2.5V
0V
C
R
V
Clamp
Gnd9
1
R
2
Sink Only
=
Positive True Logic
C
O
Figure 28. Timing Diagram
C
*
C
NC
NC
NC
NC
C
C
NC
Demag Output
Fault Latch Q
Sync Input
2.5V
0V
Startup With Foldback
Startup Without Foldback
*C = Comparison of Current Sense Input With V
MOTOROLA ANALOG IC DEVICE DATA
Clamp
Normal OperationOutput Overload
NC = No Comparison of Current Sense Input With V
Clamp
9
Page 10
MC44602
OPERA TING DESCRIPTION
The MC44602 is a high performance, fixed frequency,
current mode controller specifically designed to directly drive
a bipolar power switch in off–line and high voltage dc–to–dc
converter applications. This device offers the designer a cost
effective solution with minimal external components. The
representative block and timing diagrams are shown in
Figures 27 and 28.
Oscillator
The oscillator frequency is programmed by the values
selected for the timing components RT and CT. Capacitor C
is charged from the 5.0 V reference through resistor RT to
approximately 2.8 V and discharged to 1.2 V by an internal
current sink. During the discharge of CT, the oscillator
generates an internal blanking pulse that holds one of the
inputs of the NOR gate high. This causes the Source and
Sink outputs to be in a low state, thus producing a controlled
amount of output deadtime. An internal toggle flip–flop has
been incorporated in the MC44602 which blanks the output
off every other clock cycle by holding one of the inputs of the
NOR gate high. This in combination with the CT discharge
period yields output deadtimes programmable from 50% to
70%. Figure 1 shows RT versus Oscillator Frequency and
Figure 2, Output Deadtime versus Frequency, both for a
given value of CT. Note that many values of RT and CT will
give the same oscillator frequency but only one combination
will yield a specific output deadtime at a given frequency .
In 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 narrow rectangular
clock signal with an amplitude of 3.2 V to 5.5 V to the Sync
Input (Pin 7). For reliable locking, the free–running oscillator
frequency should be set about 10% less than the clock
frequency. If the clock signal is ac coupled through a
capacitor, an external clamp diode may be required if the
negative sync input current is greater than –5.0 mA.
Connecting Pin 7 to V
will cause CT to discharge to 0 V,
ref
inhibiting the Oscillator and conduction of the Source Output.
Multi–unit synchronization can be accomplished by
connecting the CT pin of each IC to a single MC1455 timer.
Error Amplifier
A fully compensated Error Amplifier with access to the
inverting input and output is provided. It features a typical dc
voltage gain of 90 dB, and a unity gain bandwith of
1.0 MHz with 57 degrees of phase margin (Figure 7). The
noninverting input is internally biased at 2.5 V and is not
pinned out. The converter output voltage is typically divided
down and monitored by the inverting input. The maximum
input bias current with the inverting input at 2.5 V is –2.0 µA.
This can cause an output voltage error that is equal to the
product of the input bias current and the equivalent input
divider source resistance.
The Error Amp Output (Pin 1) is provided for external loop
compensation (Figure 29). The output voltage is offset by two
diodes drops (≈1.4 V) and divided by three before it connects
to the inverting input of the Current Sense Comparator. This
guarantees that no drive pulses appear at the Source Output
(Pin 11) when Pin 1 is at its lowest state (VOL). This occurs
when the power supply is operating and the load is removed,
or at the beginning of a soft–start interval. The Error Amp
minimum feedback resistance is limited by the amplifier’s
minimum source current (0.5 mA) and the required output
voltage (VOH) to reach the comparator’s 1.0 V clamp level:
R
f(min)
3.0 (1.0 V))1.4 V
[
0.5mA
+
T
Figure 29. Error Amplifier Compensation
+
Compensation
R
FB
R
C
f
Voltage
Feedback
R
1
f
Input
R
1
2.5V
3
2
Amplifier
2.5V
From Power Supply Output
Error
I
1.0 mA
2R
Foldback
Amplifier
1.0V
Gnd
Current Sense Comparator and PWM Latch
The MC44602 operates as a current mode controller,
where output switch conduction is initiated by the oscillator
and terminated when the peak inductor current reaches the
threshold level established by the Error Amplifier output (Pin
1). Thus the error signal controls the peak inductor current on
a cycle–by–cycle basis. The Current Sense Comparator
PWM Latch configuration used ensures that only a single
pulse appears at the Source Output during the appropriate
oscillator cycle. The inductor current is converted to a voltage
by inserting the ground referenced sense resistor RS in series
with the emitter of output switch Q1. This voltage is monitored
by the Current Sense Input (Pin 6) and compared to a level
derived from the Error Amp output. The peak inductor current
under normal operating conditions is controlled by the
voltage at Pin 1 where:
lpk[
V
(Pin1)
3R
*
S
1.4V
Abnormal operating conditions occur when the power
supply output is overloaded or if output voltage sensing is
lost. Under these conditions, the Current Sense Comparator
threshold will be internally clamped to 1.0 V. Therefore the
maximum peak switch current is:
l
pk(max)
[
1.0 V
R
S
8800
R
Current Sense
Comparator
9
W
10
MOTOROLA ANALOG IC DEVICE DATA
Page 11
MC44602
A narrow spike on the leading edge of the current
waveform can usually be observed and may cause the power
supply to exhibit an instability when the output is lightly
loaded. This spike is due to the power transformer
interwinding capacitance and the output rectifier recovery
time. The addition of an RC filter on the Current Sense Input
with a time constant that approximates the spike duration will
usually eliminate the instability; refer to Figure 30.
Undervoltage Lockout
Two undervoltage lockout comparators have been
incorporated to guarantee that the IC is fully functional before
the output stage is enabled. The positive power supply
terminal (VCC) and the reference output (V
) are each
ref
monitored by separate comparators. Each has built–in
hysteresis to prevent erratic output behavior as their
respective thresholds are crossed. The VCC comparator
upper and lower thresholds are 14.1 V/10.2 V. The V
ref
comparator upper and lower thresholds are 3.6 V/3.3 V. The
large hysteresis and low startup current of the MC44602
make it ideally suited for off–line converter applications
(Figures 33, 34) where efficient bootstrap startup techniques
are required.
A 20 V zener is connected as a shunt regulator from VCC to
ground. Its purpose is to protect the IC from excessive
voltage that can occur during system startup. The upper limit
for the minimum operating voltage of the MC44602 is 1 1V.
Outputs
The MC44602 contains a high current split totem pole
output that was specifically designed for direct drive of
Bipolar Power Transistors. By splitting the totem pole into
separate source and sink outputs, the power supply designer
has the ability to independently adjust the turn–on and
turn–off base drive to the external power transistor for optimal
switching. The Source and Sink outputs are capable of up to
1.0 A and 1.5 A respectively and feature 50 ns switching
times with a 1.0 nF load. Additional internal circuitry has been
added to keep the Source Output “Off” and the Sink Output
“On” whenever an undervoltage lockout is active. This
feature eliminates the need for an external pull–down resistor
and guarantees that the power transistor will be held in the
“Off” state.
Separate output stage power and ground pins are
provided to give the designer added flexibility in tailoring the
base drive circuitry for a specific application. The Source
Output high–state is controlled by applying a positive voltage
to VC (Pin 14) and is independent of VCC. A zener clamp is
typically connected to this input when driving power
MOSFETs in systems where VCC is greater than 20V. The
Sink Output low–state is controlled by applying a negative
voltage to the Sink Ground (Pins 4, 5, 12, 13). The Sink
Ground can be biased as much as 5.0 V negative with
respect to Ground (Pin 7). Proper implementation of the V
and Sink Ground pins will significantly reduce the level of
switching transient noise imposed on the control circuitry.
This becomes particularly useful when reducing the I
clamp level.
Reference
The 5.0 V bandgap reference has a tolerance of ±6.0%
over a junction temperature range of –25°C to 85°C. Its
primary purpose is to supply charging current to the oscillator
timing capacitor. The reference has short circuit protection
and is capable of providing in excess of 20 mA for powering
additional control system circuitry.
Figure 30. Bipolar Transistor Drive
and Current Spike Suppression
I
B
+
0
Base Charge
Removal
RB1R
C
B
B2
L
B
TQ
RSQ
R
PWM
Latch
Current Sense
Comparator
Substrate
–
V
C
14
Source
11
Sink
10
Sink Gnd
4, 5, 12, 13
Current Sense
6
Thermal Protection and Package
Internal Thermal Shutdown circuitry is provided to protect
the integrated circuit in the event that the maximum junction
temperature is exceeded. When activated, typically at 160°C,
the PWM Latch is held in the “reset” state, forcing the Source
Output “Off” and the Sink Output “On”. This feature is
provided to prevent catastrophic failures from accidental
device overheating. It is not intended to be used as a
substitute for proper heatsinking.
The MC44602 is contained in a heatsinkable 16–lead
plastic dual–in–line package in which the die is mounted on a
special heat tab copper alloy lead frame. This tab consists of
the four center Sink Ground pins that are specifically
designed to improve the thermal conduction from the die to
the circuit board. Figure 14 shows a simple and effective
method of utilizing the printed circuit medium as a heat
dissipater by soldering these pins to an adequate area of
copper foil. This permits the use of standard layout and
mounting practices while having the ability to halve the
C
junction to air thermal resistance. This example is for a
symmetrical layout on a single–sided board with two ounce
per square foot of copper.
pk(max)
V
in
Q1
R
C
R
S
MOTOROLA ANALOG IC DEVICE DATA
11
Page 12
MC44602
Design Considerations
Do not attempt to construct the converter on
wire–wrap or plug–in prototype boards. High frequency
circuit layout techniques are imperative to prevent
pulse–width jitter. This is usually caused by excessive noise
pick–up imposed on the Current Sense or Voltage Feedback
inputs. Noise immunity can be improved by lowering circuit
impedances at these points. The printed circuit layout should
contain a ground plane with low–current signal, and high
current switch and output grounds returning on separate
PROTECTION MODES
The MC44602 operates as a conventional fixed frequency
current mode controller when the power supply output load is
less than the design limit. For enhanced system reliability , this
device has the unique ability of changing operating modes if
the power supply output is overloaded or shorted.
Overload Protection
Power supply overload protection is provided by the
Foldback Amplifier. As the output load gradually increases,
the Error Amplifier senses that the voltage at Pin 3 is less than
the 2.5 V threshold. This causes the voltage at Pin 1 to rise,
increasing the Current Sense Comparator threshold in order
to maintain output regulation. As the load further increases,
the inverting input of the Current Sense Comparator reaches
the internal 1.0 V clamp level, limiting the switch current to the
calculated I
pk(max)
will cause the power supply output to fall out of regulation. As
the voltage at Pin 3 falls below 2.5 V, current will flow out of
the Foldback Amplifier input, and the internal clamp level will
be proportionally reduced (Figures 9, 10). The increase in
current flowing out of the Foldback Amplifier input in
conjunction with the reduced clamp level, causes the power
supply output voltage to fall at a faster rate than the voltage at
Pin 3. This results in the output foldback characteristic shown
in Figure 31. The shape of the current limit “knee” can be
modified by the value of resistor R1 in the feedback divider.
Lower values of R1 will reduce the I
faster rate.
Improper operation of the Foldback Amp can be
encountered when the Error Amp compensation capacitor C
exceeds 2.0 nF. The problem appears at Startup when the
output voltage of the power supply is below nominal, causing
the Error Amp output to rise quickly. The rapid change in
output voltage will be coupled through Cf to the Inverting Input
(Pin 3), keeping it at its 2.5 V threshold as the 1.0 mA Error
Amp current source charges Cf. This has the effect of
disabling the Foldback Amp by preventing Pin 3 and the
clamp level at the inverting input of the Current Sense
Comparator, from rising in proportion to the power supply
output voltage. By adding resistor RFB in series with Cf, the
voltage at Pin 3 can be held to 1.0 V, corresponding to a
Current Sense clamp level of 0.08 V (Figure 10), while
allowing the Error Amp output to reach its high state VOH of
7.0 V. The required resistor to keep Pin 3 below 1.0 V during
initial Startup is:
. At this point any further increase in load
clamp level at a
2
2
RFB R
RFB + R
pk(max)
f
≥ 6
f
R1 R
R1 + R
paths back to the input filter capacitor. Ceramic bypass
capacitors (0.1 µF) connected directly to VCC, VC, and
V
may be required depending upon circuit layout. This
ref
provides a low impedance path for filtering the high frequency
noise. All high current loops should be kept as short as
possible using heavy copper runs to minimize radiated EMI.
The Error Amp compensation circuitry and the converter
output voltage divider should be located close to the IC and
as far as possible from the power switch and other noise
generating components.
Figure 31. Output Foldback Characteristic
V
VO Nominal
VCC UVLO
Threshold
out
Low Value R
New Startup
Sequence Initiated
Nominal Load
Range
l
pk(max)
1
Short Circuit Protection
Short circuit protection for the power supply is provided by
the Valid Load Comparator, Fault Latch, and Demag
Comparator. Figure 32 shows the logic truth table of the
functional blocks. When operating the power supply with
nominal output loading, the Fault Latch is “Set” by the NOR
gate driver during the Power Transistor “On” time and “Reset”
by the Fault Comparator during the “Off” time. When a severe
overload or short circuit occurs on any output, the voltage
during the “Off” time (flyback voltage) at the Load Detect
Input, is unable to reach the 2.5 V threshold of the V alid Load
Comparator. This causes the Fault Latch to remain in the
f
“Set” state with output Q
“Low”. During the “Off” time the
Demag Comparator output will also be “Low”. This causes
the NOR gate to internally hold the Sync Input “High”,
inhibiting the next fixed frequency Oscillator cycle and
switching of the Power Transistor. As the load dissipates the
stored transformer energy, the voltage at the Load Detect
Input will fall. When this voltage reaches 85 mV, the Demag
Comparator output goes “High”, allowing the Sync Input to go
“Low”, and the Power Transistor to turn “On”.
Note that as long as there is an output short, the switching
frequency will shift to a much lower frequency than that set by
RT/CT. The frequency shift has the effect of lowering the duty
cycle, resulting in a significant reduction in Power Transistor
and Output Rectifier heating when compared to conventional
current mode controllers. The extended “On” time is the result
of CT charging from 0 V to 2.8 V instead of 1.2 V to 2.8 V . The
extended “Off” time is the result of the output short time
constant. The time constant consists of the output filter
capacitance, and the equivalent series resistance (ESR) of
the capacitor plus the associated wire resistance.
During the initial power supply startup the controller
sequences through the Short Circuit and Overload Protection
modes as the output filter capacitors charge–up. If an output
is shorted and the auxiliary feedback winding is used to
power the control IC as in Figure 33, the VCC UVLO lower
threshold level will be reached after several cycles, disabling
the IC and initiating a new startup sequence. The Short
Circuit Protection mode can be disabled by grounding the
Sync Input. Narrow switching spikes are present on this pin
during normal operation. These spikes are caused by the rise
time of the flyback voltage from the 85 mV Demag
Comparator threshold to the 2.5 V Valid Load Comparator
threshold. In high power applications, the increased negative
current at the Load Detect Input can extend the switching
spikes to the point where they exceed the Sync Input
threshold. This problem can be eliminated by placing an
external small signal clamp diode at the Load Detect Input.
The diode is connected with the cathode at Pin 2 and the
anode at ground.
The divide–by–two toggle flip–flop will appear not to
function properly during power supply startup without
foldback, or operation with an overloaded output. This
phenomena appears at the end of the oscillator cycle if there
was not a current sense comparison, and after the flyback
voltage at the Load Detect Input failed to exceed 2.5 V . Under
these conditions, the Sync input will go high approximately
1.0 µs after the Load Detect Input exceeds the 85 mV Demag
Narrow spike at Sync Input (<2.5 V) as transformer voltage
rises quickly, Oscillator is not affected.
Valid Load Comparator fails to reset Fault Latch, Pulse at
Sync Input exceeds 2.5 V , Oscillator is disabled.
Comparator threshold. This causes CT to discharge down
towards ground, generating a second negative going edge
on the oscillator waveform. This second edge results in the
divide–by–two flip–flop being clocked twice for each “On”
time of the switch transistor. During initial startup, this effect
can be eliminated by insuring that the Foldback Amplifier is
fully active with the addition of resistor RFB. With the Foldback
Amplifier active, the clamp level at the inverting input of the
Current Sense Comparator will be low, allowing a comparison
to take place during the switch transistor “On” time. When the
Load Detect Input exceeds 85 mV, the Sync Input will go
high, discharging CT to ground after 1.0 µs, thus eliminating
the second negative edge. Operation with the output
overloaded will cause the toggle flip–flop to be clocked twice
for each “On” time. This should not be a problem since the
next “On” time is delayed by the Demag Comparator until the
load dissipates the transformers energy.
The point where the IC detects that there is a severe
output overload, or that the transformer has reached zero
current, is controlled by the voltage of the auxiliary winding
and a resistor divider. The divider consists of an external
series resistor and an internal shunt resistor. The shunt
resistor is nominally 18 kΩ but can range from 12 kΩ to 30 kΩ
due to process variations. If more precise overload and zero
current detection is required, the internal resistor variations
can be swamped out by connecting a low value external
resistor (≤2.7 kΩ) from Pin 2 to ground.
MOTOROLA ANALOG IC DEVICE DATA
13
Page 14
MC44602
PIN FUNCTION DESCRIPTION
PinFunctionDescription
1CompensationThis pin is the Error Amplifier output and is made available for loop compensation.
2Load Detect InputA voltage indicating a severe overload or short circuit condition at any output of the
3Voltage Feedback InputThis is the inverting input of the Error Amplifier and the noninverting input of the
4, 5, 12, 13Sink GroundThe Sink Ground pins form a single power return that is typically connected back to the
6Current Sense InputA voltage proportional to inductor current is connected to this input. The PWM uses this
7Sync InputA narrow rectangular waveform applied to this input will synchronize the Oscillator. A dc
8RT/C
9GroundThis pin is the control circuitry ground and is typically connected back to the power
10Sink OutputPeak currents up to 1.5 A are sunk by this output suiting it ideally for turning–off a bipolar
11Source OutputPeak currents up to 1.0 A are sourced by this output suiting it ideally for turning–on a
14V
15V
16V
T
C
CC
ref
switching power supply is connected to this input. The Oscillator is controlled by this
information making the power supply short circuit proof.
Foldback Amplifier. It is normally connected to the switching power supply output
through a resistor divider.
power source on a separate path from Pin 9 Ground, to reduce the effects of switching
transient noise on the control circuitry . These pins can be used to enhance the package
power capabilities (Figure 14). The Sink Output low state (VOL) can be modified by
applying a negative voltage to these pins with respect to Ground (Pin 9) to optimize
turn–off of a bipolar junction transistor .
information to terminate conduction of the output switch transistor.
voltage within the range of 3.2 V to 5.5 V will inhibit the Oscillator.
The Oscillator frequency and maximum Output duty cycle are programmed at this pin by
connecting resistor RT to V
source on a separate path from the Sink Ground (Pins 4, 5, 12, 13).
junction transistor. The output switches at one–half the oscillator frequency.
bipolar junction transistor. The output switches at one–half the oscillator frequency.
The Output high state (VOH) is set by the voltage applied to this pin. With a separate
connection to the power source, it can reduce the effects of switching transient noise on
the control circuitry.
This pin is the positive supply of the control IC. The minimum operating voltage range
after startup is 11 V to 18 V.
This is the 5.0 V reference output. It provides charging current for capacitor CT through
resistor RT and can be used to bias any additional system circuitry.
and capacitor CT to ground.
ref
14
MOTOROLA ANALOG IC DEVICE DATA
Page 15
MC44602
Figure 33. 60 Watt Off–Line Flyback Regulator
85 to 265
2.2
Vac
1N4148
0.1470pF
0.1µF
24k
47k
10k
470k
1.0k
10k
2.2nF
1.0nF
1N5404
15k
1N4148
1
2
3
4
5
6
7
8
470
270
15
14
12
MC44602
11
10
16
13
220pF
390
T1
47k
2.0W
MUR
4100
220
0.1
85V/0.5A
220pF
1N4934
µ
H
1.0
MUR
415
470
0.1 20V/0.6A
220pF
8.2k
2.0W
220
3.3nF
1.0
22
0.33
µ
H
9
47
MUR
460
47nF
MBR
340
470pF
MJE18006
470
0.1
6.8V/0.8A
1.0nF/1.0kV
1.0k
0.82
4.7M
TestConditionsResults
Line Regulation
85V
20V
6.8V
Load Regulation
85V
20V
6.8V
Vin = 85 Vac to 265 Vac
IO = 0.5 A
IO = 0.5 A
IO = 0.8 A
Vin = 220 Vac
IO = 0.1 A to 0.5 A
IO = 0.1 A to 0.5 A
IO = 0.1 A to 0.8 A
∆ = 1.0 V or ± 0.6%
∆ = 0.04 V or ± 0.1%
∆ = 0.07 V or ± 0.5%
∆ = 1.0 V or ± 0.6%
∆ = 0.4 V or ± 1.0%
∆ = 0.2 V or ± 1.5%
EfficiencyVin = 110 Vac, PO = 58 W81%
Standby PowerVin = 110 Vac, PO = 0 W2.0 W
T1
–
Orega SMT2 (G4787–01)
Primary: 41 Turns, #25AWG
Auxiliary Feedback: 12 Turns, #25AWG
Secondary: 85 V – 60 Turns, #25A WG
Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty , representation or guarantee regarding
the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation consequential or incidental damages. “T ypical” parameters which may be provided in Motorola
data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals”
must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of
others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other
applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury
or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola
and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees
arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola
was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal
Opportunity/Affirmative Action Employer.
How to reach us:
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INTERNET: http://Design–NET.com51 Ting Kok Road, Tai Po, N.T ., Hong Kong. 852–26629298
18
◊
MOTOROLA ANALOG IC DEVICE DATA
MC44602/D
*MC44602/D*
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