MAX6900 データシートの表示（PDF） - Maxim Integrated

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MAX6900

I2C-Compatible RTC in a TDFN

Maxim Integrated 

I2C-Compatible RTC in a TDFN

RAM burst mode is specified, no data transfer occurs

to any of the RAM locations. Burst writes of data greater

than 31 bytes could cause erroneous data in the

MAX6900.

Power-On Reset (POR)

The MAX6900 contains an integral POR circuit that

ensures all registers are reset to a known state on

power-up. Once VCC rises above 1.6V (typ), the POR

circuit releases the registers for normal operation.

When VCC drops to less than 1.6V (typ), the MAX6900

resets all register contents to the POR defaults.

Oscillator Startup

The MAX6900 oscillator typically takes 5s to 10s to

begin oscillating. To ensure the oscillator is operating

correctly, the software should validate proper time-

keeping. This is accomplished by reading the Seconds

register. Any reading of 1s or more from the POR is a

validation of proper startup.

Reserved Register

This is reserved for factory testing ONLY. Do not write

to this register. If inadvertent Writes are done to this

register, cycle power on the MAX6900.

Crystal Selection

Connect a 32.768kHz watch crystal directly to the

MAX6900 through pin 2 and pin 3 (X1, X2). Use a crys-

Rf

MAX6900

Rd

Cg

Cd

25pF

25pF

X1

X2

EXTERNAL

CRYSTAL

Figure 9. Oscillator Functional Schematic

tal with a specified load capacitance (CL) of 12.5pF.

See Table 4 for a list of crystal parameters.

Table 5 lists some crystal manufacturers and part num-

bers for their surface-mount 32.768kHz watch crystals

that require 12.5pF. In addition, these manufacturers

offer other package options depending upon the spe-

cific application considerations.

Frequency Stability Overtemperature

Timekeeping accuracy of the MAX6900 is dependent

on the frequency stability of the external crystal. To

Table 4. Quartz Crystal Parameters

PARAMETER

SYMBOL

Frequency

f

Equivalent Series Resistance (ESR)

Rs

Parallel Load Capacitance

CL

Q Factor

Q

MIN

40

11.2

40,000

TYP

32.768

12.5

MAX

60

13.7

60,000

UNITS

kHz

kΩ

pF

Table 5. Crystal Manufacturers

MANUFACTURER

Abracon Corporation

Caliber Electronics

ECS INC International

Fox Electronics

M-tron

Raltron

SaRonix

MANUFACTURER

PART NO.

ABS25-32.768-12.5-B-

AWS2A-32.768KHz

ECS-.327-12.5-17

FSM327

SX2010/SX2020

RSE-32.768-12.5-C-T

32S12A

TEMP.

RANGE

-40°C to +85°C

-20°C to +70°C

-10°C to +60°C

-40°C to +85°C

-20°C to +75°C

-10°C to +60°C

-40°C to +85°C

CL (pF)

12.5

12.5

12.5

12.5

12.5

12.5

12.5

+25°C FREQUENCY

TOLERANCE (ppm)

±20

±20

±20

±20

±20

±20

±20

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