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NTE1753 Datasheet, PDF (1/4 Pages) NTE Electronics – Integrated Circuit Pulse Width Modulator (PWM) Control Circuit | |||
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NTE1753
Integrated Circuit
Pulse Width Modulator (PWM) Control Circuit
Description:
The NTE1753 is a fixedâfrequency pulse width modulation control circuit in a 14âLead DIP type pack-
age incorporating the primary building blocks required for the control of a switching power supply.
An internalâlinear sawtooth oscillator frequency is determined by:
1.1
fOSC ^ RT D CT
Output pulse width modulation is accomplished by comparison of the positive sawtooth waveform
across capacitor CT 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-
trolâsignal amplitude causes a corresponding linear decrease of output pulse width.
The control signals are external inputs that can be fed into the deadâtime control, the error amplifier
inputs, or the feedâback input. The deadâtime control comparator has an effective 120mV input offset
which limits the minimum output dead time to approximately the first 4% of the sawtoothâcycle 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 timeâcontrol 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 onâtime, 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 commonâ
mode input range from â0.3V to (VCC â2V), and may be used to sense power supply output voltage
and current. The errorâamplifier outputs are active high and are 0 red together at the nonâinverting
input of the pulseâwidth 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 ±5% with a typical thermal drift of less
than 50mV over an operating temperature range of 0 to +70°C.
Features:
D Complete Pulse Width Modulation Control Circuitry
D OnâChip Oscillator with Master or Slave Operation
D OnâChip Error Amplifiers
D OnâChip 5.0 Volt Reference
D Adjustable Dead Time Control
D Uncommitted Output Transistor for 200mA Source or Sink
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