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MC33304P

Low Voltage Rail-to-Rail SLEEPMODE Operational Amplifier

Motorola => Freescale 

MC33304

DEVICE DESCRIPTION

The MC33304 will begin to function at power supply

voltages as low as VS = ±0.8 V. The device has the ability to

swing rail–to–rail on both the input and the output. Since the

common mode input voltage range extends from VCC to VEE,

it can be operated with either single or split voltage supplies.

The MC33304 is guaranteed not to latch up or phase reverse

over the entire common mode range. However, the output

could go into phase reversal state if input voltage is set higher

than +VCC or –VEE.

When power is initially applied, the part may start to

operate in the awakemode. This occurs because of bias

currents being generated from the charging of the internal

capacitors. When this occurs, the user will have to wait

approximately 1.5 seconds before the device will switch back

to the sleepmode.

The amplifier is designed to switch from sleepmode to

awakemode whenever the output current exceeds a preset

current threshold (ITH) of approximately 200 µA. As a result,

the output switching threshold voltage (VST) is controlled by

the output loading resistance (RL). Large valued load

resistors require a large output voltage to switch, but reduce

unwanted transitions to the awakemode.

Most of the transition time is consumed slewing in the

sleepmode until VST is reached, therefore, small values of RL

allow rapid transition to the awakemode. The output

switching threshold voltage (VST) is higher for the larger

values of RL, requiring the amplifier to slew longer in the

slower sleepmode state before switching to the awakemode.

Although typically 200 µA, ITH varies with supply voltage,

temperature and the load resistance. Generally, any current

loading on the ouput which causes a current greater than ITH

to flow will switch the amplifier into the awakemode. This

includes transition currents like those generated by charging

load capacitances. In fact, the maximum capacitance that

can be driven while attempting to remain in the sleepmode is

approximately 300 pF.

The awakemode to sleepmode transition time is controlled

by an internal delay circuit, which is necessary to prevent the

amplifier from going to sleep during every zero crossing of

the output waveform. This delay circuit also eliminates the

crossover distortion commonly found in micropower

amplifiers.

The MC33304 rail–to–rail sleepmode operational amplifier

is unique in its ability to swing rail–to–rail on both the input

and output using a bipolar design. This offers a low noise and

wide common mode input voltage range. Since the common

mode input voltage range extends from VCC to VEE, it can be

operated with either single or split voltage supplies.

Rail–to–rail performance is achieved at the input of the

amplifiers by using parallel NPN–PNP differential input

stages. When the inputs are within 800 mV of the negative

rail, the PNP stage is on. When the inputs are more than

800 mV above VEE, the NPN stage is on. This switching of

input pairs will cause a reversal of input bias currents. Also,

slight differences in offset voltage may be noted between the

NPN and PNP pairs. Cross–coupling techniques have been

used to keep this change to a minimum.

In addition to the rail–to–rail performance, the output stage

is current boosted to provide enough output current to drive

600 Ω loads. Because of this high current capability, care

should be taken not to exceed the 150°C maximum junction

temperature specification.

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MOTOROLA ANALOG IC DEVICE DATA

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