Z8F1680SH020SG Datasheet, PDF (221/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
196
Chapter 15. Low-Power Operational
Amplifier
The low-power operational amplifier is a standard operational amplifier designed for
current measurements. Each of the three ports of the amplifier is accessible from the
package pins. The inverting input is commonly used to connect to the current source. The
output node connects an external feedback network to the inverting input. The non-
inverting output is required to apply a nonzero bias point. In a standard single-supply
system, this bias point must be substantially above ground to measure positive input
currents. The noninverting input can also be used for offset correction.
Note: This amplifier is a voltage gain operational amplifier. Its transimpedance nature is deter-
mined by the feedback network.
The low-power operational amplifier contains only one pin configuration; ANA0 is the
output/feedback node, ANA1 is the inverting input and ANA2 is the noninverting input.
To use the low-power operational amplifier, it must be enabled in the Power Control Reg-
ister Definitions, discussed on page 44. The default state of the low-power operational
amplifier is OFF. To use the low-power operational amplifier, the TRAM bit must be
cleared, turning it ON (see Power Control Register 0 on page 44). When making normal
ADC (i.e., not transimpedance) measurements on ANA0, the TRAM bit must be OFF.
Turning the TRAM bit ON interferes with normal ADC measurements. Finally, this bit
enables the amplifier even in STOP Mode. If the amplifier is not required in STOP Mode,
disable it. Failing to perform this results in STOP Mode currents greater than specified.
As with other ADC measurements, any pins used for analog purposes must be configured
as in the GPIO registers (see the Port A–E Alternate Function Subregisters on page 61).
Standard transimpedance measurements are made on ANA0 as selected by the
ANAIN[3:0] bits of the ADC Control Register 0, discussed on page 189. It is also possible
to make single-ended measurements on ANA1 and ANA2 when the amplifier is enabled
which is often useful for determining offset conditions.
PS025015-1212
PRELIMINARY
Low-Power Operational Amplifier