MAXQ3180-RAN+ datasheet(9/48 Pages) MAXIM

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Reset Sources

There are several different sources that can cause the

MAXQ3180 to undergo a reset cycle. For any type of

hardware reset, the RESET pin is driven low when a

reset occurs.

External Reset

This hardware reset is initiated by an external source

(such as the master controller or a manual pushbutton

press) driving the RESET pin on the MAXQ3180 low.

The RESET line must be held low for at least four cycles

of the currently selected clock for the external reset to

take effect. Once the external reset takes effect, it

remains in effect indefinitely as long as RESET is held

low. Once the external reset has been released, the

MAXQ3180 clears all registers to their default states

and resumes execution in Initialization Mode.

When an external reset occurs outside of Stop Mode,

execution (in Initialization Mode) resumes after four

cycles of the currently selected clock (external high-fre-

quency crystal for Run Mode, 1MHz internal RC oscilla-

tor for LPMM Mode). As the MAXQ3180 enters

Initialization Mode, the LOWPM bit is always cleared to

0, meaning that the MAXQ3180 always switches to the

high-frequency clock before it begins accepting com-

mands in Initialization Mode.

When an external reset occurs from Stop Mode, execu-

tion (in Initialization Mode) resumes after 128 cycles of

the internal RC oscillator (or approximately 128μs).

Power-On Reset

When the MAXQ3180 is first powered up, or when the

power supply, DVDD, drops below the VRST power-fail

trip point (outside of Stop Mode), the MAXQ3180 is

held in power-on reset. Once the power supply rises

above the VRST level, the power-on reset state is

released and all registers are reset to their defaults and

execution resumes in Initialization Mode. The high-fre-

quency external crystal (LOWPM = 0) is always select-

ed as the clock source following any power-on or

brownout reset.

In Stop Mode brownout detection is disabled, so a

power-on reset does not occur until DVDD drops to a

lower level (VPOR). From the master’s perspective,

power-on resets and brownout resets both cause the

MAXQ3180 to reset in the same way.

Watchdog Reset

The MAXQ3180 includes a hardware watchdog timer that

is armed and periodically reset automatically during nor-

mal operation. Under normal circumstances, the

MAXQ3180 always resets the watchdog timer often

enough to prevent it from expiring. However, if an internal

Low-Power, Multifunction, Polyphase AFE

_______________________________________________________________________________________

CLOCK

RESET

SAMPLING

INTERNAL

RESET

BEGIN RUNNING IN INITIALIZATION MODE

Figure 2. External Reset

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