A resistor ladder and three connected multiplexers are associated with each op amp,
as shown in Figure 1. These multiplexers are configured using the MUXTOP,
MUXBOT and MUXWIP bit fields of the Op Amp n Resistor Ladder Multiplexer
(OPAMP.OPnRESMUX) register. If the OPnRESMUX register is changed while the OPn output is
enabled, a glitch will occur on the output signal due to the opening and closing of
analog switches, and some time will elapse before the output settles to the new
value.
The top of the resistor ladder is connected to a multiplexer that is
controlled by the MUXTOP bit field. It can connect to the following signals:
- OFF - Multiplexer off, no signal
connected
- OUT (OPnOUT) - OPn output
- VDD - VDD
The bottom of the resistor ladder is also connected to a multiplexer. This
multiplexer is controlled by the MUXBOT bit field, and it can connect to the following
signals:
- OFF - Multiplexer off, no signal
connected
- INP (OPnINP) - Positive input pin
for OPn
- INN (OPnINN) - Negative input pin
for OPn
- DAC - DAC output (DAC and DAC
output buffer must be enabled)
- GND - Ground
OP0 has the following additional connection
available via the MUXBOT bit field:
- LINKOUT (OP2OUT) - OP2
output
OP1 has the
following additional connection available via the MUXBOT bit field:
- LINKOUT (OP0OUT) - OP0
output
OP2 has the following additional connection
available via the MUXBOT bit field:
- LINKOUT (OP1OUT) - OP1
output
A third multiplexer is connected to eight different wiper positions on the
resistor ladder. This multiplexer is controlled by the MUXWIP bit field and allows the
OPnWIP signal to be connected to any of eight different ratios of the upper (R2) and
lower (R1) resistors:
- WIP0 - R2/R1 = 1/15
- WIP1 - R2/R1 = 1/7
- WIP2 - R2/R1 = 1/3
- WIP3 - R2/R1 = 1
- WIP4 - R2/R1 = 5/3
- WIP5 - R2/R1 = 3
- WIP6 - R2/R1 = 7
- WIP7 - R2/R1 = 15
The tolerances of the resistor ratios, as well as the absolute values and
tolerances of the resistors, are specified in the Electrical Characteristics
section.