MC34060A Datasheet, PDF (6/16 Pages) ON Semiconductor – Fixed Frequency, PWM, Voltage Mode Single Ended Controllers

MC34060A, MC33060A
APPLICATIONS INFORMATION
The control signals are external inputs that can be fed into
the dead−time control, the error amplifier inputs, or the
feed−back input. The dead−time control comparator has an
effective 120 mV input offset which limits the minimum
output dead time to approximately the first 4% of the
sawtooth−cycle time. This would result in a maximum duty
cycle of 96%. Additional dead time may be imposed on the
output by setting the dead time−control input to a fixed
voltage, ranging between 0 V to 3.3 V.
The pulse width modulator comparator provides a means
for the error amplifiers to adjust the output pulse width from
the maximum percent on−time, established by the dead time
control input, down to zero, as the voltage at the feedback
pin varies from 0.5 V to 3.5 V. Both error amplifiers have a
common mode input range from −0.3 V to (V_CC −2.0 V), and
may be used to sense power supply output voltage and
current. The error−amplifier outputs are active high and are
ORed together at the noninverting input of the pulse−width
modulator comparator. With this configuration, the
amplifier that demands minimum output on time, dominates
control of the loop.
The MC34060A has an internal 5.0 V reference capable
of sourcing up to 10 mA of load currents for external bias
circuits. The reference has an internal accuracy of ±5% with
a typical thermal drift of less than 50 mV over an operating
temperature range of 0° to +70°C.
500 k
100 k
0.001 mF
V_CC = 15 V
10 k
C_T = 0.01 mF
1.0 mF
1.0 k
500
1.0 k
2.0 k 5.0 k 10 k 20 k 50 k 100 k 200 k 500 k 1.0 M
R_T, TIMING RESISTANCE (W)
Figure 3. Oscillator Frequency
versus Timing Resistance
120
110
VCC = 15 V
100
DVO = 3.0
V
90
RL = 2.0 kW
0
80
A_VOL
-20
70
-40
60
q
-60
50
-80
40
-100
30
-120
20
-140
10
0
1.0
10
-160
-180
100 1.0 k 10 k 100 k 1.0 M
f, FREQUENCY (Hz)
Figure 4. Open Loop Voltage Gain and Phase
versus Frequency
20
18
16
14
12
C_T = 0.001 mF
10
8.0
6.0
0.01 mF
4.0
2.0
0
500 1.0 k
10 k
100 k
f_osc, OSCILLATOR FREQUENCY (Hz)
500 k
Figure 5. Percent Deadtime versus
Oscillator Frequency
100
80
V_CC = 15 V
C_T = 0.001
R_T = 47 k
60
40
20
0
0
1.0
2.0
3.0
3.5
DEAD-TIME CONTROL VOLTAGE (V)
Figure 6. Percent Duty Cycle versus
Dead−Time Control Voltage
http://onsemi.com
6