7

OPA336, 2336, 4336

®

FIGURE 4. Small-Signal Step Response Using Series Re-

sistor to Improve Capacitive Load Drive.

50

µs/div

FIGURE 2. Input Current Protection for Voltages Exceeding

the Supply Voltage.

CAPACITIVE LOAD AND STABILITY

OPA336 series op amps can drive a wide range of capaci-

tive loads. However, all op amps under certain conditions

may become unstable. Op amp configuration, gain, and

load value are just a few of the factors to consider when

determining stability.

When properly configured, OPA336 series op amps can

drive approximately 10,000pF. An op amp in unity gain

configuration is the most vulnerable to capacitive load. The

capacitive load reacts with the op amp’s output resistance,

along with any additional load resistance, to create a pole in

the response which degrades the phase margin. In unity gain,

OPA336 series op amps perform well with a pure capacitive

load up to about 300pF. Increasing gain enhances the

amplifier’s ability to drive loads beyond this level.

One method of improving capacitive load drive in the unity

gain configuration is to insert a 50

Ω to 100Ω resistor inside

the feedback loop as shown in Figure 3. This reduces ringing

with large capacitive loads while maintaining DC accuracy.

R

S

100

Ω

OPAx336

C

L

R

L

V

IN

V

OUT

FIGURE 3. Series Resistor in Unity-Gain Configuration

Improves Capacitive Load Drive.

FIGURE 1. No Phase Inversion with Inputs Greater than the

Power Supply Voltage.

APPLICATIONS INFORMATION

OPA336 series op amps are fabricated on a state-of-the-art

0.6 micron CMOS process. They are unity-gain stable and

suitable for a wide range of general purpose applications.

Power supply pins should be bypassed with 0.01

µF ceramic

capacitors. OPA336 series op amps are protected against

reverse battery voltages.

OPERATING VOLTAGE

OPA336 series op amps can operate from a +2.1V to +5.5V

single supply with excellent performance. Most behavior

remains unchanged throughout the full operating voltage

range. Parameters which vary significantly with operating

voltage are shown in the typical performance curves. OPA336

series op amps are fully specified for operation from +2.3V

to +5.5V; a single limit applies over the supply range. In

addition, many parameters are guaranteed over the specified

temperature range, –40

°C to +85°C.

INPUT VOLTAGE

The input common-mode range of OPA336 series op amps

extends from (V–) –0.2V to (V+) –1V. For normal opera-

tion, inputs should be limited to this range. The absolute

maximum input voltage is 300mV beyond the supplies.

Thus, inputs greater than the input common-mode range

but less than maximum input voltage, while not valid, will

not cause any damage to the op amp. Furthermore, the

inputs may go beyond the power supplies without phase

inversion (Figure 1) unlike some other op amps.

6V

0V

Normally, input bias current is approximately 1pA. How-

ever, input voltages exceeding the power supplies can

cause excessive current to flow in or out of the input pins.

Momentary voltages greater than the power supply can be

tolerated as long as the current on the input pins is limited

to 10mA. This is easily accomplished with an input resis-

tor as shown in Figure 2.

5k

Ω

OPAx336

10mA max

+5V

V

IN

V

OUT

I

OVERLOAD