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13

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Frequency

f

32.768

kHz

Equivalent Series Resistance (ESR)

40

60

k

Ω

Parallel Load Capacitance

11.2

12.5

13.7

pF

Q Factor

Q

40,000

60,000

Table 4. Quartz Crystal Parameters

MANUFACTURER

MANUFACTURER

PART NO.

TEMP.

RANGE

+25

°C FREQUENCY

TOLERANCE (ppm)

Abracon Corporation

ABS25-32.768-12.5-B-

-40°C to +85°C

12.5

±20

Caliber Electronics

AWS2A-32.768KHz

-20°C to +70°C

12.5

±20

ECS INC International

ECS-.327-12.5-17

-10°C to +60°C

12.5

±20

Fox Electronics

FSM327

-40°C to +85°C

12.5

±20

M-tron

SX2010/SX2020

-20°C to +75°C

12.5

±20

Raltron

RSE-32.768-12.5-C-T

-10°C to +60°C

12.5

±20

SaRonix

32S12A

-40°C to +85°C

12.5

±20

Table 5. Crystal Manufacturers

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

circuit releases the registers for normal operation.

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-

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

Rf

Rd

Cd

25pF

Cg

25pF

EXTERNAL

CRYSTAL

X1

X2

MAX6900

Figure 9. Oscillator Functional Schematic