Datasheet

OA Operation www.ti.com
20.2.1 OA Amplifier
The OA is a configurable, low-current, rail-to-rail output operational amplifier. It can be configured as an
inverting amplifier, or a non-inverting amplifier, or can be combined with other OA modules to form
differential amplifiers. The output slew rate of the OA can be configured for optimized settling time vs
power consumption with the OAPMx bits. When OAPMx = 00 the OA is off and the output is high-
impedance. When OAPMx > 0, the OA is on. See the device-specific data sheet for parameters.
20.2.2 OA Input
The OA has configurable input selection. The signals for the + and - inputs are individually selected with
the OANx and OAPx bits and can be selected as external signals or internal signals. OAxI0 and OAxI1 are
external signals provided for each OA module. OA0I1 provides a non-inverting input that is tied together
internally for all OA modules. OAxIA and OAxIB provide device-dependent inputs. See the device data
sheet for signal connections.
When the external inverting input is not needed for a mode, setting the OANEXT bit makes the internal
inverting input externally available.
20.2.3 OA Output and Feedback Routing
The OA has configurable output selection controlled by the OAADCx bits and the OAFCx bits. The OA
output signals can be routed to ADC inputs A12 (OA0), A13 (OA1), or A14 (OA2) internally, or can be
routed to these ADC inputs and their external pins. The OA output signals can also be routed to ADC
inputs A1 (OA0), A3 (OA1), or A5 (OA2) and the corresponding external pin. The OA output is also
connected to an internal R-ladder with the OAFCx bits. The R-ladder tap is selected with the OAFBRx bits
to provide programmable gain amplifier functionality.
Table 20-1 shows the OA output and feedback routing configurations. When OAFCx = 0 the OA is in
general-purpose mode and feedback is achieved externally to the device. When OAFCx > 0 and when
OAADCx = 00 or 11, the output of the OA is kept internal to the device. When OAFCx > 0 and
OAADCx = 01 or 10, the OA output is routed both internally and externally.
Table 20-1. OA Output Configurations
OAFCx OAADCx OA Output and Feedback Routing
= 0 x0 OAxOUT connected to external pins and ADC input A1, A3, or A5.
= 0 x1 OAxOUT connected to external pins and ADC input A12, A13, or A14.
> 0 00 OAxOUT used for internal routing only.
> 0 01 OAxOUT connected to external pins and ADC input A12, A13, or A14.
> 0 10 OAxOUT connected to external pins and ADC input A1, A3, or A5.
OAxOUT connected internally to ADC input A12, A13 , or A14. External A12, A13, or A14 pin
> 0 11
connections are disconnected from the ADC.
20.2.4 OA Configurations
The OA can be configured for different amplifier functions with the OAFCx bits as listed in Table 20-2.
Table 20-2. OA Mode Select
OAFCx OA Mode
000 General-purpose opamp
001 Unity gain buffer for three-opamp differential amplifier
010 Unity gain buffer
011 Comparator
100 Non-inverting PGA amplifier
101 Cascaded non-inverting PGA amplifier
110 Inverting PGA amplifier
111 Differential amplifier
514
OA SLAU144J–December 2004–Revised July 2013
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated