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KA3524
SMPS Controller
Features
Complete PWM power control circuit
Operation beyond 100KHz
2% frequency stability with temperature
Total quiescent current less than 10mA
Single ended or push-pull outputs
Current limit amplifier provides external component
protection
• On-chip protection against excessive junction temperature
and output current
• 5V, 50mA linear regulator output available to user
•
•
•
•
•
•
Description
The KA3524 regulating pulse width modulator contains
all of the control circuit necessary to implement switching
regulators of either polarity, transformer coupled DC to
DC converters, transformerless polarity converters and volt-
age doublers, as well as other power control applications.
This device includes a 5V voltage regulator capable of sup-
plying up to 50mA to external circuit , a control ampli-
fier, an oscillator, a pulse width modulator, a phase
splitting flip-flop, dual alternating output switch transistors,
and current limiting and shut-down circuit. Both the regu-
lator output transistor and each output switch are internally
current limiting and, to limit junction temperature, aninter-
nal thermal shutdown circuit is employed.
16-DIP
1
Internal Block Diagram
Rev. 5.0
©2000 Fairchild Semiconductor International
KA3524
Absolute Maximum Ratings
Parameter
Supply Voltage
Reference Output Current
Output Current (Each Output)
Oscillator Charging Current (pin 6 or 7)
Lead Temperature (Soldering, 10 sec)
Power Dissipation (T
A
= 25°C)
Operating Temperature
Storage Temperature
Symbol
V
CC
I
REF
I
O
I
CHG(OSC
)
T
LEAD
P
D
T
POR
T
STG
Value
40
50
100
5
300
1000
0 ~ +70
-65 ~ + 150
Unit
V
mA
mA
mA
°C
mW
°C
°C
Electrical Characteristics
(V
IN
=20V, f=20KHz, T
A
= 0 to +70°C, unless otherwise specified)
Parameter
REFERENCE SECTION
Reference Output Voltage
Line Regulation
Load Regulation
Ripple Rejection
Short-Circuit Output Current
Temperature Stability
Long Term Stability
OSCILLATOR SECTION
Maximum Frequency
Initial Accuracy
Frequency Change with Voltage
Frequency Change with
Temperature
Clock Amplitude (Pin 3)
Clock Width (Pin 3)
ERROR AMPLIFIER SECTION
Input Offset Voltage
Input Bias Current
Open Loop Voltage Gain
Common-Mode Input Voltage
Common-Mode Rejection Ratio
Small Signal Bandwidth
Output Voltage Swing
V
IO
I
BIAS
G
VO
V
CM
CMRR
BW
SS
V
O(ERR)
T
A
= 25°C
T
A
= 25°C
G
V
= 0dB, T
A
= 25°C
T
A
= 25°C
V
CM
= 2.5V
V
CM
= 2.5V
-
-
-
60
1.8
-
-
0.5
2
2
80
-
70
3
-
10
10
-
3.4
-
-
3.8
mV
µA
dB
V
dB
MHz
V
f
(MAX)
ACCUR
∆f/∆V
CC
∆f/∆T
V
(CLK)
t
W(CLK)
C
T
= 0.001uF, R
T
= 2KΩ
R
T
and C
T
constant
V
CC
= 8V to 40V, T
A
= 25°C
Over operating temperature range
T
A
= 25°C
C
T
= 0.01uF, T
A
= 25°C
-
-
-
-
-
-
350
5
-
-
3.5
0.5
-
-
1
2
-
-
KHz
%
%
%
V
µs
V
REF
∆V
REF
∆V
REF
RR
I
SC
ST
T
ST
T
A
= 25°C
-
V
CC
= 8V to 40V
I
REF
= 0 mA to 20 mA
f = 120Hz, T
A
= 25°C
V
REF
= 0, T
A
= 25°C
-
4.6
-
-
-
-
-
-
5.0
10
20
66
100
0.3
20
5.4
30
50
-
-
1
-
V
mV
mV
dB
mA
%
mV/KHr
Symbol
Conditions
Min.
Typ.
Max.
Unit
2
KA3524
Electrical Characteristics
(V
IN
=20V, f=20KHz, T
A
=0°C to +70°C, unless otherwise specified)
Parameter
COMPARATOR SECTION
Maximum Duty Cycle
Input Threshold (Pin 9)
Input Threshold (Pin 9)
Input Bias Current
CURRENT LIMITING SECTION
Sense Voltage
V
SENSE
V
2
- V
1
≥50mV
V
9
= 2V, T
A
= 25°C
-
-
-
V
CE
= 40V
I
C
= 50mA
V
C
= 20V
R
C
= 2KΩ, T
A
= 25°C
R
C
= 2KΩ, T
A
= 25°C
V
CC
=40V, PINS 1,4,7,8,11
and 14 are grounded, V
2
=2V
All other inputs and Outputs open
180
-
0.7
40
-
-
17
-
-
-
200
0.2
-
-
0.1
1
18
0.2
0.1
5
220
-
1
-
50
2
-
-
-
10
mV
mV/°C
V
V
µA
V
V
µs
µs
mA
D
(MAX)
V
TH1
V
TH2
I
BIAS
% Each output on
Zero duty cycle
Maximum duty cycle
-
45
-
-
-
-
1
3.5
1
-
-
-
-
%
V
V
µA
Symbol
Conditions
Min. Typ. Max. Unit
Temperature Coefficient of Vsense
∆V
SENSE
/∆T
Common-Mode Voltage
OUTPUT SECTION (EACHOUTPUT)
Collector-Emitter Voltage
Collector Leakage Current
Saturation Voltage
Emitter Output Voltage
Rise Time (10 to 90)
Fall Time (90 to 10)
Supply Current
V
CEO
I
LKG
V
CE(SAT)
V
E
t
R
t
F
I
CC
V
CM
3
KA3524
Application Information
Voltage Reference
An internal series regulator provides a nominal 5 volt output which is used both to generate a reference voltage and is
the regulated source for all the internal timing and controlling circuitry. This regulator may be bypassed for operation
from a fixed 5 volt supply by connecting pins 15 and 16 together to the input voltage. In this configuration, the maximum
input voltage is 6.0 volts.
This reference regulator may be used as a 5 volt source for other circuitry. It will provide up to 50mA of current itself
and can easily be expanded to higher current with an external PNP as shown in Figure 2.
Expanded Reference Current Capability
Oscillator
The oscillator in the KA3524 uses an external resistor (R
T
) to establish a constant charging current into an external capacitor
(C
T
), While this uses more current than a series connected PC, it provides a linear ramp voltage on the capacitor which is also
used as a reference for the comparator. The charging current is equal to 3.6V/R
T
and should be kept within the range of
approximately 30uA to 2mA, i.e., 1.8K< R
T
<100K. The range of values for C
T
also has limits as the discharge time of C
t
determines the pulse width of the oscillator output pulse. This pulse is used (among other things) as a blanking pulse to both
outputs to insure that there is no possibility of having both outputs on simultaneously during transitions. This output dead time
relationship is shown in Figures. A pulse width below approximately 0.5 microseconds may allow false triggering of one out-
put by removing he blanking pulse prior to the flip-flops reaching a stable state. If small values of C
T
must be used, the pulse
width may still be expanded by adding a shunt capacitance (= 100pF) to ground at the oscillator output. (Note: Although the
oscillator output is a convenient oscilloscope sync input, the cable and input capacitance may increase the blanking pulse
width slightly.) Obviously, the upper limit of the pulse width is determined by the maximum duty cycle acceptable. Practical
values of C
T
fall between 0.01 and0.1 micro farad. The oscillator period is approximately t = R
T
C
T
where t is in microsec-
onds when R
T
ohms and C
T
= micro farads. The selection of R
T
and C
T
can be made for a wide range of operating frequen-
cies by using Fig. 7. Note that for sense regulator applications, the two outputs can be connected in parallel for an effective 0-
90% duty cycle and the frequency of the oscillator is the frequency of the output. For push-pull applications, the outputs are
separated and the flip-flop divides the frequency such that each output duty cycle is 0-45% and the overall frequency is one-
half that of the oscillator.
External Synchronization
If It is desired to synchronize the KA3524 to an external clock, a pulse of +3 volts may be applied to the oscillator output
terminal with R
T
C
T
set slightly greater than the clock period. The same considerations of pulse width apply. The impedance to
ground at this point is approximately 2K ohms. If two or more KA3524s must be synchronized together, one must be desig-
nated as the master with its R
T
C
T
set for the correct period. The slaves should each have an R
T
C
T
set for an approximately
10% longer period than the master with the added requirement that C
T
(slave) = one-half C
T
(master). Then connecting Pin 3
on all units together will insure that the master output pulse-which occurs first and has a wider pulse width - will reset the
slave units.
4
KA3524
Error Amplifier
This circuit is a simple differential-input, transconductance amplifier. The output is the compensation terminal pin 9, which is
a high impedance node (R
L:
=5MΩ). The gain is
G
V
= gmR
L
=
8I
L
R
L
= 0.002 R
L
--------------
-
2K
T
and can easily be reduced from a nominal of 10,000 by an external shunt resistance from pin 9 to ground, as shown in Figure
8,In addition to DC gain control, the compensation terminal is also the place for AC phase compensation. The frequency
response curves of Figure 5 show the uncompensated amplifier with a single pole at approximately 200Hz and a unity gain
cross-over frequency at 5MHz.typically, most output filter designs will introduce one or more addition poles at a significantly
higher power frequency. Therefore, the best stabilizing network is a series R-C combination between pin 9 and ground which
introduces a zero to cancel one of the output filter poles. A good starting point is 50KΩ plus 0.001 micro farad. One final point
on the compensation terminal is that this is also a convenient place to insert any programming signal which is to override the
error amplifier. Internal shutdown and current limit circuits are connected here, but any other circuit which can sink 200uA
can pull this point to ground, thus shutting off both outputs. While feedback is normally applied around the entire regulator, the
error amplifier can be used with conventional operational amplifier feedback and is stable in either the inverting or non-
inverting mode. Regardless of the connections, however, input common-mode limits must be observed or output sign inver-
sions may happen. For conventional regulator applications, the 5 volt reference voltage must be divided down as shown in Fig-
ure 3. The error amplifier may also be used in fixed duty cycle applications by using the unity gain configuration shown in the
open loop test circuit.
Current Limiting
The current limiting circuitry of the KA3524 is shown in Figure 4.
By matching the base-emitter voltages of Q1 and Q2, and assuming negligible voltage drop across R
1
:
Threshold = V
BE
(Q1) + I
1
R
2
- V
BE
(Q2)
= l
1
R
2
= 200mV
Although this circuit provides a relatively small threshold with a negligible temperature coefficient, there are some limitations
to its use, the most important of which is the
±1
volt common mode range which requires sensing in the ground line. Another
factor to consider is that the frequency compensation provided by R
1
C
1
and Q1 provides a roll-off pole at approximately
300Hz.Since the gain of this circuit is relatively low, there is a transition region as the current limit amplifier takes over pulse
width control from the error amplifier. For testing purposes, the threshold is defined as the input voltage to get 25% duty cycle
with the error amplifier signaling maximum duty cycle. In addition to constant current limiting, pins 4 and 5 may also be used
in transformer-coupled circuits to sense primary current and shorten an output pulse, should transformer saturation occur.
Another application is to ground pin 5 and use pin 4 as an additional shutdown terminal: i.e., the output will be off with pin 4
open and on when it is grounded. Finally, fold back current limiting can be provided with the network of Figure 5. This cir-
cuit can reduce the short circuit current (l
SC
)to approximately one third the maximum available output current (I
MAX
).
Figure 3. Error Amplifier Biasing Circuits
5
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