Datasheet

20 s/divm
V
IN
50mV/div
100mV/div
V
OUT
20 s/divm
V
IN
50mV/div
100mV/div
V
OUT
OPA827
www.ti.com SBOS376H –NOVEMBER 2006–REVISED MAY 2012
CAPACITIVE LOAD AND STABILITY
The combination of gain bandwidth product (GBW)
and near constant open loop output impedance (Z
O
)
over frequency gives the OPA827 the ability to drive
large capacitive loads. Figure 44 shows the OPA827
connected in a buffer configuration (G = +1) while
driving a 2.2μF ceramic capacitor (with an ESR value
of approximately 0Ω). The small overshoot and fast
settling time are results of good phase margin. This
feature provides superior performance compared to
the competition. Figure 44 and Figure 45 were taken
without any resistive load in parallel to shorten the
ringing time.
In Figure 45, the OPA827 is driving a 2.2μF tantalum
Figure 44. OPA827 Driving 2.2μF Ceramic
capacitor. A relatively small ESR that is internal to the
Capacitor
capacitor additionally improves phase margin and
provides an output waveform with no ringing and
minimal overshoot. Figure 45 shows a stable system
that can be used in almost any application.
Capacitive load drive depends on the gain and
overshoot requirements of the application. Capacitive
loads limit the bandwidth of the amplifier. Increasing
the gain enhances the ability of the amplifier to drive
greater capacitive loads (see Figure 28).
PHASE-REVERSAL PROTECTION
The OPA827 family has internal phase-reversal
protection. Many FET-input op amps exhibit a phase
reversal when the input is driven beyond its linear
common-mode range. This condition is most often
encountered in noninverting circuits when the input is
Figure 45. OPA827 Driving 2.2μF Tantalum
driven beyond the specified common-mode voltage
Capacitor
range, causing the output to reverse into the opposite
rail. The input circuitry of the OPA827 prevents phase
reversal with excessive common-mode voltage;
instead, the output limits into the appropriate rail (see
Figure 29).
Copyright © 2006–2012, Texas Instruments Incorporated 15