Texas Instruments DAC8580, Руководство пользователя

Страница: 10 / 23

EVM Operation
www.ti.com
3.3 The Output Operational Amplifier
The EVM includes an optional signal-conditioning circuit for the DAC output through an external
operational amplifier, U2. The output operational amplifier is set to unity gain configuration by default.
Nevertheless, the raw output of the DAC can be probed through the even pins of the output terminal, J4.
The inverting input of U2 can be tied to the gain resistor, R12 (via W15) or the DAC output (by shorting
pins 3 and 4 of the J3 header) or to any voltage source through J3-4.
The following sections describe the different configurations of the output amplifier, U2. This operational
amplifier can be used to serve as buffer to unload the DAC and also different signal conditioning and
amplification purposes desired.
This buffering circuit may present some slight distortion because of the feedback resistor and capacitor. If
this is the case, users can easily configure the feedback circuit to closely match the 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.
3.3.1 Unity Gain Output
Table 2 shows the jumper setting for the unity gain configuration of the DAC output buffer in unipolar or
bipolar mode.
Table 2. Unity Gain Output Jumper Settings
Jumper Position
Reference Unipolar Bipolar Function
J3 2-3 2-3 Routes the DAC output to the noninverting terminal of the output operational amplifier, U2.
W15 OPEN OPEN Disconnect the inverting input of the operational amplifier, U2, from gain resistor, R12.
W5 2-3 1-2 Negative rail of operational amplifier is tied to AGND or powered by V
SS
.
3.3.2 Output Gain of Two
Table 3 shows the proper jumper settings of the EVM for the 2× gain output of the DAC.
Table 3. Gain of Two Output Jumper Settings
Jumper Position
Reference Unipolar Bipolar Function
J3 2-3 2-3 Routes the DAC output to the noninverting terminal of the operational amplifier, U2.
W15 CLOSED CLOSED Inverting input of the output operational amplifier, U2, is connected to gain resistor, R12, to
set for a gain of 2.
W5 2-3 1-2 Supplies power, V
SS
, to the negative rail of operational amplifier, U2, for bipolar supply mode
or ties it to AGND for unipolar supply mode.
3.3.3 Output Gain of Five With DAC V
OUT
Inverted
Table 4 shows the proper jumper settings of the EVM to achieve a gain of five with the output of the DAC
inverted.
Table 4. Jumper Settings for a Gain of Five With Inverted Output
Jumper Position
Reference Unipolar Bipolar Function
J3 1-2 & 3-4 1-2 & 3-4 Output of DAC is inverted with a gain of five. Watch for clipping due to operational amplifier
headroom issue.
W15 OPEN OPEN Disconnect the inverting input of operational amplifier, U2, from the gain resistor, R12.
W5 2-3 1-2 Supplies power, V
SS
, to the negative rail of operational amplifier, U2, for bipolar supply
mode, or ties it to AGND for unipolar supply mode.
10 DAC8580/81 Evaluation Module SLAU173A – December 2005 – Revised November 2009
Submit Documentation Feedback
Copyright © 2005–2009, Texas Instruments Incorporated