M41T93SQA6E View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

M41T93SQA6E

Serial SPI bus RTC with battery switchover

STMicroelectronics 

Clock operation

M41T93

Note:

Two methods are available for ascertaining how much calibration a given M41T93 may

require:

● The first involves setting the clock, letting it run for a month and comparing it to a known

accurate reference and recording deviation over a fixed period of time. This allows the

designer to give the end user the ability to calibrate the clock as the environment

requires, even if the final product is packaged in a non-user serviceable enclosure. The

designer could provide a simple utility that accesses either or both of the Calibration

bytes.

● The second approach is better suited to a manufacturing environment, and involves the

use of the IRQ/FT/OUT pin. The IRQ/FT/ OUT pin will toggle at 512Hz when FT and

OUT Bits = '1' and ST = '0.' Any deviation from 512Hz indicates the degree and

direction of oscillator frequency shift at the test temperature. For example, a reading of

512.010124Hz would indicate a +20 ppm oscillator frequency error, requiring either a –

10 (xx001010) to be loaded into the Digital Calibration byte, or +6pF (00011000) into

the Analog Calibration byte for correction.

Setting or changing the Digital Calibration Byte does not affect the Frequency Test, Square

Wave, or Watchdog Timer frequency, but changing the Analog Calibration byte DOES affect

all functions derived from the low current oscillator (see Figure 12).

Figure 12. Clock divider chain and calibration circuits

512Hz Output

Frequency Test

32kHz

CXI

CXO

÷2

÷2

÷2

÷2

÷2

Low Current

Oscillator

÷8

Digital Calibration Circuitry

(divide by 511/512/513)

1Hz Signal

Remainder of

Divider Circuit

Square Wave

Watchdog Timer

8-Bit Timer

Clock

Registers

Analog Calibration

Circuitry

AI11806a

26/51

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