MAXQ3180-RAN+ datasheet(18/101 Pages) MAXIM

18 / 101 page

Low-Power, Multifunction, Polyphase AFE

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same manner as if an external reset had taken place.

Unlike a hardware reset, however, a software reset does

not cause the MAXQ3180 to drive the RESET line low.

Power-Supply Monitoring

In addition to the hardware reset provided by the

power-on reset and brownout reset circuits, the

MAXQ3180 includes the capability to detect a low

power supply on the DVDD pin and alert the master

through the interrupt (IRQ) mechanism before a hard-

ware reset occurs. This function, which is always

enabled outside of Stop Mode, causes the RAM status

ever VDVDD drops below the VPFW trip point. Once

PWRF has been set to 1 by hardware, it can only be

cleared by the master (or by a system reset). Whenever

PWRF = 1, if the EPWRF interrupt masking bit is also

set to 1, the MAXQ3180 drives IRQ low to signal to the

master that an interrupt condition (in this case, a power-

fail warning) exists and requires attention.

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 3.

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.

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 could 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

XTAL IN

RING IN

SYSTEM CLOCK

EXTCLK

STOPM

POR

CLK

ENABLE

WATCHDOG RESET

RING COUNT

INT/EXT

CRYSTAL

STARTUP TIMER

WATCHDOG TIMER

1MHz

INTERNAL

OSCILLATOR

CRYSTAL

ENABLE

CLOCK

GENERATION

Figure 3. Simplified Clock Sources

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