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Am186TMER and Am188TMER Microcontrollers Data Sheet

DRAF

LOW-VOLTAGE OPERATION

The low-voltage operation of the Am186ER and

Am188ER microcontrollers is an enabling technology

for the design of portable systems with long battery life.

This capability, combined with CPU clock management,

enables design of very low-power computing systems.

Low-Voltage Standard

Industry standards for low-voltage operation are

emerging to facilitate the design of components that

will make up a complete low-voltage system. As a

guideline, the Am186ER and Am188ER microcontrol-

ler specifications follow the first article or regulated ver-

sion of the JEDEC 8.0 low-voltage proposal. This

standard proposal calls for a VCC range of 3.3 V ± 10%.

Power Savings

CMOS dynamic power consumption is proportional to

the square of the operating voltage multiplied by capac-

itance and operating frequency. Static CPU operation

can reduce power consumption by enabling the system

designer to reduce operating frequency when possible.

However, operating voltage is always the dominant fac-

tor in power consumption. By reducing the operating

voltage from 5 V to 3.3 V for any device, the power

consumed is reduced by 56%.

Reduction of CPU and core logic operating voltage dra-

matically reduces overall system power consumption.

Additional power savings can be realized as low-voltage

mass storage and peripheral devices become available.

Two basic strategies exist in designing systems con-

taining the Am186ER and Am188ER microcontrollers.

The first strategy is to design a homogenous system in

which all logic components operate at 3.3 V. This pro-

vides the lowest overall power consumption. However,

system designers may need to include devices for

which 3.3-V versions are not available. In the second

strategy, the system designer must then design a

mixed 5-V/3.3-V system. This compromise enables the

system designer to minimize the core logic power con-

sumption while still including functionality of the 5-V

features. The choice of a mixed voltage system design

also involves balancing design complexity with the

need for the additional features.

Input/Output Circuitry

To accommodate current 5-V systems, the Am186ER

and Am188ER microcontrollers have 5-V tolerant I/O

drivers. The drivers produce TTL-compatible drive out-

put (minimum 2.4-V logic High) and receive TTL and

CMOS levels (up to VCC + 2.6 V). The following are

some design issues that should be considered when

upgrading an Am186ER microcontroller 5-V design:

n During power-up, if the 3.3-V supply has a signifi-

cant delay in achieving stable operation relative to

5-V supply, then the 5-V circuitry in the system may

start driving the processor’s inputs above the maxi-

mum levels (VCC + 2.6 V). The system design

should ensure that the 5-V supply does not exceed

2.6 V above the 3.3-V supply during a power-on se-

quence.

n Preferably, all inputs will be driven by sources that

can be three-stated during a system reset condition.

The system reset condition should persist until sta-

ble VCC conditions are met. This should help ensure

that the maximum input levels are not exceeded

during power-up conditions.

n Preferably, all pullup resistors will be tied to the

3.3-V supply, which will ensure that inputs requiring

pullups are not over stressed during power-up.

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