NTE1753
Integrated Circuit
Pulse Width Modulator (PWM) Control Circuit
Description:
The NTE1753 is a fixed鈥揻requency pulse width modulation control circuit in a 14鈥揕ead DIP type pack-
age incorporating the primary building blocks required for the control of a switching power supply.
An internal鈥搇inear sawtooth oscillator frequency is determined by:
1.1
f
OSC
^
R
T
D
C
T
Output pulse width modulation is accomplished by comparison of the positive sawtooth waveform
across capacitor C
T
to either of two control signals. The output is enabled only during that portion
of time when the sawtooth voltage is greater than the control signals. Therefore, an increase in con-
trol鈥搒ignal amplitude causes a corresponding linear decrease of output pulse width.
The control signals are external inputs that can be fed into the dead鈥搕ime control, the error amplifier
inputs, or the feed鈥揵ack input. The dead鈥搕ime control comparator has an effective 120mV input offset
which limits the minimum output dead time to approximately the first 4% of the sawtooth鈥揷ycle time.
This would result in a maximum duty cycle of 96%. Additional dead time may be imposed on the out-
put by setting the dead time鈥揷ontrol input to a fixed voltage, ranging between 0 to 3.3V.
The pulse width modulator comparator provides a means for the error amplifiers to adjust the output
pulse width from the maximum percent on鈥搕ime, established by the dead time control input, down to
zero, as the voltage at the feedback pin varies from 0.5 to 3.5V. Both error amplifiers have a common鈥?/div>
mode input range from 鈥?.3V to (V
CC
鈥?V), and may be used to sense power supply output voltage
and current. The error鈥揳mplifier outputs are active high and are 0 red together at the non鈥搃nverting
input of the pulse鈥搘idth modulator comparator. With this configuration, the amplifier that demands
minimum output on time, dominates control of the loop.
The NTE1753 has an internal 5.0V reference capable of sourcing up to 10mA of load currents for ex-
ternal bias circuits. The reference has an internal accuracy of
鹵5%
with a typical thermal drift of less
than 50mV over an operating temperature range of 0 to +70擄C.
Features:
D
Complete Pulse Width Modulation Control Circuitry
D
On鈥揅hip Oscillator with Master or Slave Operation
D
On鈥揅hip Error Amplifiers
D
On鈥揅hip 5.0 Volt Reference
D
Adjustable Dead Time Control
D
Uncommitted Output Transistor for 200mA Source or Sink
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