Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

OPA2690 Datasheet(PDF) 21 Page - Burr-Brown (TI)

[Old version datasheet] Texas Instruments acquired Burr-Brown Corporation. Click here to check the latest version.
Part No. OPA2690
Description  Dual, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable
Download  30 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  BURR-BROWN [Burr-Brown (TI)]
Homepage  http://www.burr-brown.com
Logo BURR-BROWN - Burr-Brown (TI)

OPA2690 Datasheet(HTML) 21 Page - Burr-Brown (TI)

Back Button OPA2690 Datasheet HTML 17Page - Burr-Brown (TI) OPA2690 Datasheet HTML 18Page - Burr-Brown (TI) OPA2690 Datasheet HTML 19Page - Burr-Brown (TI) OPA2690 Datasheet HTML 20Page - Burr-Brown (TI) OPA2690 Datasheet HTML 21Page - Burr-Brown (TI) OPA2690 Datasheet HTML 22Page - Burr-Brown (TI) OPA2690 Datasheet HTML 23Page - Burr-Brown (TI) OPA2690 Datasheet HTML 24Page - Burr-Brown (TI) OPA2690 Datasheet HTML 25Page - Burr-Brown (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 21 / 30 page
background image
OPA2690
SBOS238D − JUNE 2002 − REVISED DECEMBER 2004
www.ti.com
21
DRIVING CAPACITIVE LOADS
One of the most demanding and yet very common load
conditions for an op amp is capacitive loading. Often, the
capacitive load is the input of an ADC—including
additional
external
capacitance
which
may
be
recommended to improve ADC linearity. A high-speed,
high open-loop gain amplifier like the OPA2690 can be
very susceptible to decreased stability and closed-loop
response peaking when a capacitive load is placed directly
on the output pin. When the open-loop output resistance
of the amplifier is considered, this capacitive load
introduces an additional pole in the signal path that can
decrease the phase margin. Several external solutions to
this problem have been suggested. When the primary
considerations are frequency response flatness, pulse
response fidelity, and/or distortion, the simplest and most
effective solution is to isolate the capacitive load from the
feedback loop by inserting a series-isolation resistor
between the amplifier output and the capacitive load. This
does not eliminate the pole from the loop response, but
rather shifts it and adds a zero at a higher frequency. The
additional zero acts to cancel the phase lag from the
capacitive load pole, thus increasing the phase margin and
improving stability.
The Typical Characteristics show the recommended RS
versus capacitive load and the resulting frequency
response at the load. Parasitic capacitive loads greater
than 2pF can begin to degrade the performance of the
OPA2690. Long PC board traces, unmatched cables, and
connections to multiple devices can easily exceed this
value. Always consider this effect carefully, and add the
recommended series resistor as close as possible to the
OPA2690 output pin (see the Board Layout Guidelines
section).
The criterion for setting this RS resistor is a maximum
bandwidth, flat frequency response at the load. For the
OPA2690 operating in a gain of +2, the frequency
response at the output pin is already slightly peaked
without the capacitive load requiring relatively high values
of RS to flatten the response at the load. Increasing the
noise gain will reduce the peaking as described previously.
The circuit of Figure 13 demonstrates this technique,
allowing lower values of RS to be used for a given
capacitive load.
1/2
OP A26 90
402
175
402
+5V
50
50
C
LOAD
R
NG
V
O
R
−5V
Power−supply decoupling
not shown.
Figure 13. Capacitive Load Driving with Noise
Gain Tuning
This gain of +2 circuit includes a noise gain tuning resistor
across the two inputs to increase the noise gain,
increasing the unloaded phase margin for the op amp.
Although this technique will reduce the required RS
resistor for a given capacitive load, it does increase the
noise at the output. It also will decrease the loop gain,
slightly decreasing the distortion performance. If, however,
the dominant distortion mechanism arises from a high RS
value, significant dynamic range improvement can be
achieved using this technique. Figure 14 shows the
required RS versus CLOAD parametric on noise gain using
this technique. This is the circuit of Figure 13 with RNG
adjusted to increase the noise gain (increasing the phase
margin) then sweeping CLOAD and finding the required RS
to get a flat frequency response. This plot also gives the
required RS versus CLOAD for the OPA2690 operated at
higher signal gains without RNG.
100
90
80
70
60
50
40
30
20
10
0
Capacitive Load (pF)
1
10
100
1000
NG = 2
NG = 3
NG = 4
Figure 14. Required RS vs Noise Gain


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30 


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn