OPA320 datasheet(15/37 Pages) NSC

15 / 37 page

3000

CapacitiveLoad(pF)

2500

500

1000

1500

2000

G=1,V =1.8V

G=1,V =5.5V

G=10,V =1.8V

G=10,V =5.5V

0.5

1.5

2.5

9.75

Time(250ns/div)

10.25

10.5

10.75

Output

Input

V = 2.75V

G= 10

20W

V+

OUT

OPA320

2.5

1.5

0.5

9.75

Time(250ns/div)

10.25

10.5

10.75

Input

Output

V = 2.75V

G= 10

OPA320, OPA2320

OPA320S, OPA2320S

www.ti.com

SBOS513E – AUGUST 2010 – REVISED JUNE 2013

The equivalent series resistance (ESR) of some very

OVERLOAD RECOVERY TIME

large capacitors (CL > 1µF) is sufficient to alter the

Overload recovery time is the time it takes the output

phase characteristics in the feedback loop such that

of the amplifier to come out of saturation and recover

the amplifier remains stable. Increasing the amplifier

to the linear region. Overload recovery is particularly

closed-loop

gain

allows

the

amplifier

drive

important in applications where small signals must be

increasingly

larger

capacitance.

This

increased

amplified

the

presence

large

transients.

capability is evident when observing the overshoot

Figure 38 and Figure 39 show the positive and

response of the amplifier at higher voltage gains, as

negative overload recovery times of the OPA320,

shown in Figure 37. One technique for increasing the

respectively. In both cases, the time elapsed before

capacitive load drive capability of the amplifier

the OPA320 comes out of saturation is less than

operating in unity gain is to insert a small resistor

100ns. In addition, the symmetry between the positive

(RS), typically 10Ω to 20Ω, in series with the output,

and negative recovery times allows excellent signal

as shown in Figure 36.

rectification without distortion of the output signal.

This resistor significantly reduces the overshoot and

ringing associated with large capacitive loads. A

possible problem with this technique is that a voltage

divider is created with the added series resistor and

any resistor connected in parallel with the capacitive

load. The voltage divider introduces a gain error at

the output that reduces the output swing. The error

contributed

the

voltage

divider

may

insignificant. For instance, with a load resistance, RL

= 10k

Ω and RS = 20Ω, the gain error is only about

0.2%. However, when RL is decreased to 600Ω,

which the OPA320 is able to drive, the error

increases to 7.5%.

Figure 38. Positive Recovery Time

Figure 36. Improving Capacitive Load Drive

Figure 39. Negative Recovery Time

Figure 37. Small-Signal Overshoot versus

Capacitive Load (100mVPPoutput step)

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