MAXQ3180(2008) Ver la hoja de datos (PDF) - Maxim Integrated

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Fabricante

MAXQ3180
(Rev.:2008)

Low-Power, Multifunction, Polyphase AFE

Maxim Integrated 

Low-Power, Multifunction, Polyphase AFE

Clock Sources

All operations including ADC sampling and SPI com-

munications are synchronized to a single system clock.

This clock can be obtained from any one of three selec-

table sources, as shown in Figure 4.

External High-Frequency Crystal

The default system clock source for the MAXQ3180 is

an external high-frequency crystal oscillator circuit con-

nected between XTAL1 and XTAL2. When clocked with

an external crystal, a parallel-resonant, AT-cut crystal

oscillating in the fundamental mode is required. The

typical values of the external load capacitors vary with

the type of crystal being used and should be selected

based on the load capacitance as suggested by the

crystal manufacturer.

When using a high-frequency crystal, the fundamental

oscillation mode of the crystal operates as inductive

reactance in parallel resonance with external capaci-

tors C1 and C2. The typical values of these external

capacitors vary with the type of crystal being used and

should be selected based on the load capacitance as

suggested by the crystal manufacturer.

Since noise at XTAL1 and XTAL2 can adversely affect

device timing, the crystal and capacitors should always

be placed as close as possible to the XTAL1 and

XTAL2 pins, with connection traces between the crystal

and the device kept as short and direct as possible. In

multiple layer boards, avoid running other high-speed

digital signals underneath the crystal oscillator circuit if

possible, as this may inject unwanted noise into the

clock circuit.

Following power-up or any system reset, the high-fre-

quency clock is automatically selected as the system

clock source. However, before this clock can be used

for system execution, a crystal warmup timer must

count 65,536 cycles of the high-frequency clock. While

this warmup time period is in effect, execution contin-

ues using the internal 1MHz oscillator. Once the

65,536-cycle count completes (which requires approxi-

mately 8.2ms at 8MHz), the device automatically

switches over to the high-frequency clock. This crystal

warmup timer is also activated upon exit from Stop

Mode, since the high-frequency crystal oscillator is shut

down during Stop Mode.

External High-Frequency Clock

Instead of using a crystal oscillator to generate the

high-frequency clock, it is also possible to input a high-

frequency clock that has been generated by another

source (such as a digital oscillator IC) directly into the

XTAL1 pin of the MAXQ3180.

To use an external high-frequency clock as the system

clock source, the XTAL1 pin should be used as the

HF

CRYSTAL

1MHz

INTERNAL

OSCILLATOR

CLOCK

GENERATION

ENABLE

SYSTEM CLOCK

EXTCLK

STOPM

POR

INT/EXT

XTAL IN

RING IN

CRYSTAL

STARTUP TIMER

RING COUNT

WATCHDOG TIMER

CLK

ENABLE

WATCHDOG RESET

Figure 4. Simplified Clock Sources

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