Sensors

Freescale Semiconductor

13

MMA690xQ

Figure 2-4 Voltage Monitoring

2.3

OSCILLATOR

An internal oscillator operating at a nominal frequency of 4.0 MHz provides a stable clock source. The oscillator is factory

trimmed for best performance. A clock generator block divides the 4.0 MHz clock as needed by other blocks.

2.4

A monitor circuit is incorporated to ensure predictable operation of the device in the event that the connection to the external

circuitry for 2.0

μs every 249.5 μs. If the external capacitor is not present, voltage at the internal supply rail will drop below the

internal reset threshold, continuously forcing the device into reset. Loss of communication from the device is a readily detectable

2.5

CLOCK MONITOR

Two independent oscillators are provided within MMA690xQ. One is factory-trimmed and provides the timing reference used

throughout the device. The second oscillator acts as a reference for the first. If the frequency of these two oscillators varies by

to be forced to a continuous logic high state when CS is asserted, as described in Section 3.1.1.2.

POR

REFER TO SECTION 5.3 FOR

POWER-ON RESET THRESHOLD

LIMITS.

+

-

+

-

+

-

+

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VOLTAGE

DIVIDER

VOLTAGE

DIVIDER

VOLTAGE

DIVIDER

VOLTAGE

DIVIDER

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VOLTAGE

DIVIDER

+

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VOLTAGE

DIVIDER

OV

UV

UV

UV

OV

OV

+

-

VOLTAGE

DIVIDER

UV