Easy Definition of Error Amplifiers

Both error amplifiers are high gain amplifiers which operate as single-ended single-supply amplifiers, in that each output is active high only. This allows each amplifier to pull up independently for a decreasing output pulse width demand. With the outputs ORed together, the amplifier with the higher output level dominates. The open loop gain of these amplifiers is 60 dB. Both error amplifiers exhibit a response time of about 400 ns from their inputs to their outputs on pin 3. Figure 6-16 shows the amplifier transfer characteristics and a Bode plot of the gain curves.

Figure 6-16. Amplifier Performance Curves

Output Logic Control

The output control logic interfaces the pulse width modulator to the output stages. In the single-ended mode (both outputs conducting simultaneously) the pulse width modulated signal is gated through to both output stages when the output control (pin 13) is connected to ground.

For push-pull operation (each output stage conducting alternately) the output control (pin 13) is connected to the internal reference voltage (pin 14) enabling the pulse steering flip-flop. The flip-flop is toggled on the trailing edge of the pulse width modulated signal gating it to each of the outputs alternately; therefore, the switching frequency of each output is one-half the oscillator frequency, The output control (pin 13) must never be left open. It may be connected to the internal voltage reference (pin 14) or ground (pin 7).