OPA300 Datasheet, PDF (11/15 Pages) Burr-Brown (TI) – Low-Noise, High-Speed, 16-Bit Accurate, CMOS OPERATIONAL AMPLIFIER

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DRIVING CAPACITIVE LOADS
When using high−speed operational amplifiers, it is
extremely important to consider the effects of
capacitive loading on amplifier stability. Capacitive
loading will interact with the output impedance of the
operational amplifier, and depending on the capacitor
value, may significantly decrease the gain bandwidth,
as well as introduce peaking. To reduce the effects of
capacitive loading and allow for additional capacitive
load drive, place a series resistor between the output
and the load. This will reduce available bandwidth, but
permit stable operation with capacitive loading.
Figure 3 illustrates the recommended relationship
between the resistor and capacitor values.
100
75
50
OPA300
OPA301
SBOS271A − MAY 2003 − REVISED DECEMBER 2003
DRIVING A 16-BIT ADC
The OPA30x features excellent THD+noise, even at
frequencies greater than 1MHz, with a 16-bit settling
time of 150ns. Figure 4 shows a total single supply
solution for high-speed data acquisition. The OPA30x
directly drives the ADS8401, a 1.25 mega sample per
second (MSPS) 16-bit data converter. The OPA30x is
configured in an inverting gain of 1, with a 5V single
supply. Results of the OPA30x performance are
summarized in Table 1.
130pF
(mica)
1820Ω
5V
1820Ω
V_IN
130pF
OPA30x
(mica)
f_S = 1.25MSPS
f = 10kHz
10Ω
ADS8401
1.5nF
25
0
1
10
100
Capacitive Load (pF)
Figure 3. Recommended R_S and C_L Combinations
Amplifiers configured in unity gain are most susceptible
to stability issues. The typical characteristic, Frequency
Response vs Capacitive Load, describes the relation-
ship between capacitive load and stability for the
OPA30x. In unity gain, the OPA300 is capable of driving
a few picofarads of capacitive load without compromis-
ing stability. Board level parasitic capacitance can often
fall into the range of a picofarad or more, and should be
minimized through good circuit-board layout practices
to avoid compromising the stability of the OPA30x. For
more information on detecting parasitics during testing,
see the Application Note Measuring Board Parasitics in
High-Speed Analog Design (SBOA094), available at
the TI web site www.ti.com.
Figure 4. The OPA30x Drives the 16-Bit ADS8401
PARAMETER
RESULTS (f = 10kHz)
THD
−99.3dB
SFDR
101.2dB
THD+N
84.2dB
SNR
84.3dB
Table 1. OPA30x Performance Results Driving a
1.25MSPS ADS8401
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