Datasheet

OPA890
5.56kW
½
DAC7822
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
DB8
DB9
DB10
DB11
V
R
R
I
I
R
R
R
REF
1
FB
OUT1
OUT2
2
2_3
3
GNDV
DD
+5V
2.5pF
+7.5V
-2.5V
V
OUT
0V V 5V£ £
OUT
0.1 Fm
-5V
OPA890
+5V
+V
S
DIS
V /2
S
698W
100WV
O
V
I
50W
59W
698W
0.1 Fm
0.1 Fm
+
6.8 Fm0.1 Fm
R
G
750W
R
F
750W
50 SourceW
83
77
71
65
59
53
47
41
Frequency(Hz)
Gain(dB)
100k 1M 10M 100M
OPA890
SBOS369B –MAY 2007–REVISED DECEMBER 2009 www.ti.com
The frequency response of the schematic shown in
Figure 48 is shown in Figure 49.
Figure 48. DAC Transimpedance Amplifier
Figure 47. AC-Coupled, G = +2, Single-Supply,
Specification and Test Circuit
Again, an additional resistor (50Ω, in this case) is
included directly in series with the noninverting input.
This minimum recommended value provides part of
the dc source resistance matching for the
noninverting input bias current. It is also used to form
a simple parasitic pole to roll off the frequency
response at very high frequencies ( > 500MHz) using
the input parasitic capacitance to form a bandlimiting
pole. The gain resistor (R
G
) is ac-coupled, giving the
circuit a dc gain of +1, which puts the input dc bias
voltage (2.5V) at the output as well. The voltage can
swing to within 1.35V of either supply pin. Driving a
demanding 100Ω load to a midpoint bias is used in
Figure 49. OPA890 (as DAC Transimpedance
this characterization circuit. Higher swings are
Amplifier) Frequency Response
possible using a lighter load.
MULTIPLYING DAC SINGLE-ENDED OUTPUT
TRANSIMPEDANCE AMPLIFIER
Multiplying digital-to-analog converters (DACs), such
as the DAC7822, can make good use of the
low-power, high slew rate amplifier, OPA890.
16 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA890