ZUSBOPTSC01ZACG datasheet(156/282 Pages) ZILOG

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PS022827-1212

P R E L I M I N A R Y

Low Power Operational Amplifier

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.

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.

Caution:

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