Z8F082ASJ020EG Datasheet, PDF (156/282 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F082A Series
Product Specification
139
Low Power Operational Amplifier
The LPO is a general-purpose low power operational amplifier. Each of the three ports of
the amplifier is accessible from the package pins. The LPO contains only one pin configu-
ration: ANA0 is the output/feedback node, ANA1 is the inverting input and ANA2 is the
noninverting input.
Operation
To use the LPO, it must be enabled in the Power Control Register 0 (PWRCTL0). The default
state of the LPO is OFF. To use the LPO, the LPO bit must be cleared by turning it ON (for
details, see the Power Control Register 0 section on page 33). When making normal ADC
measurements on ANA0 (i.e., measurements not involving the LPO output), the LPO bit
must be turned OFF. Turning the LPO bit ON interferes with normal ADC measurements.
Caution: The LPO 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 higher
than necessary.
As with other ADC measurements, any pins used for analog purposes must be configured
as such in the GPIO registers. See the Port A–D Alternate Function Subregisters section
on page 47 for details.
LPO output measurements are made on ANA0, as selected by the ANAIN[3:0] bits of
ADC Control Register 0. It is also possible to make single-ended measurements on ANA1
and ANA2 while the amplifier is enabled, which is often useful for determining offset con-
ditions. Differential measurements between ANA0 and ANA2 may be useful for noise
cancellation purposes.
If the LPO output is routed to the ADC, then the BUFFMODE[2:0] bits of ADC Control/Sta-
tus Register 1 must also be configured for unity-gain buffered operation. Sampling the
LPO in an unbuffered mode is not recommended.
When either input is overdriven, the amplifier output saturates at the positive or negative
supply voltage. No instability results.
PS022827-1212
PRELIMINARY
Low Power Operational Amplifier