Texas Instruments DAC8801/11EVM, Руководство пользователя

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EVM Operation
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6.3 The Output Operational Amplifiers
The EVM includes operational amplifiers for various applications. The U5 operational amplifier is used to
convert the current output of the MDAC to voltage output. Though the option of voltage output is
implemented, the current output, I
OUT
, can still be monitored through J4 output header, via pins 12, 14,
and 16.
The footprint of U5 is very common for most operational amplifiers; therefore, it is easy to find an
operational amplifier that suits each specific application.
The following sections describe the different configurations of the output amplifier, U4A. This additional
operational amplifier can be used to serve as buffer to unload the I-to-V circuit of the MDAC. It can also be
used for different signal conditioning and amplification purposes desired. The EVM comes configured with
the U4A operational amplifier set to a gain of five configuration. If a gain of two is desired, the inverting
input of U4A can be tied to AGND (via W15) to achieve this specific configuration. In addition, the inverting
input of U4A can also be connected to the MDAC voltage output (by shorting pins 1 and 2 of the J5
header) or to any voltage source through J5-1.
This buffering circuit may present some slight distortion because of the feedback resistor and capacitor. If
this is the case, the user can easily configure the feedback circuit to closely match their desired wave
shape by simply removing R6 and C12 and replacing it with the proper values. Additionally, C12 can be
removed altogether and R6 can be replaced with a 0-
Ω resistor if desired.
6.3.1 Unity Gain Output
Table 2 shows the jumper setting for the unity gain configuration of the MDAC output buffer in unipolar or
bipolar supply mode.
Table 2. Unity Gain Output Jumper Settings
Jumper Setting
Reference Unipolar Bipolar Function
J5 2-3 2-3 Routes the MDAC output to the noninverting terminal of the U4A.
W15 OPEN OPEN Disconnect the inverting input of operational amplifier, U4A, from AGND.
W5 2-3 1-2 Negative rail of operational amplifier is tied to AGND or powered by V
SS
.
6.3.2 Gain of Two Output Jumper Settings
Table 3 shows the proper jumper settings of the EVM for the 2× gain output of the MDAC.
Table 3. Gain of Two Output Jumper Settings
Jumper Setting
Reference Unipolar Bipolar Function
J5 2-3 2-3 Routes the MDAC output to the noninverting terminal of the U4A.
Inverting input of the output operational amplifier, U4A, is connected to AGND to set for a
W15 CLOSED CLOSED
gain of 2.
Supplies power, V
SS
, to the negative rail of operational amplifier, U4A, for bipolar supply
W5 2-3 1-2
mode, or ties it to AGND for unipolar supply mode.
10 DAC8801/11EVM SLAU151A – January 2005 – Revised November 2009
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