Z8 Encore! XP® 4K Series
Product Specification
123
Signals outside the allowable input range can be used without instability or device dam-
age. Any ADC readings made outside the input range are subject to greater inaccuracy
than specified.
Low-Power Operational Amplifier (LPO)
The LPO is a general-purpose operational amplifier. Each of the three ports of the ampli-
fier is accessible from the package pins. The LPO contains only one pin configuration:
ANA0 is the output/feedback node, ANA1 is the inverting input and ANA2 is the non-
inverting input.
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, turning it
ON (Power Control Register 0 (PWRCTL0) on page 31). When making normal ADC
measurements on ANA0 (measurements not involving the LPO output), the LPO bit must
be OFF. Turning the LPO 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 speci-
fied.
As with other ADC measurements, any pins used for analog purposes must be configured
as such in the GPIO registers (see Port A–D Alternate Function Sub-Registers on
page 42).
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. Using 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.
PS022815-0206
Analog-to-Digital Converter
ZILOG [ ZILOG, INC. ]
