Rainbow Electronics MAX6900 - Manual (Page 13)

MAX6900
I
2
C-Compatible RTC in a TDFN
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PARAMETER SYMBOL MIN TYP MAX UNITS
Frequency f 32.768 kHz
Equivalent Series Resistance (ESR) R s 40 60 k Ω
Parallel Load Capacitance C L 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
C L (pF)
+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
power-up. Once V
CC rises above 1.6V (typ), the POR
circuit releases the registers for normal operation.
When V
CC 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-
tal with a specified load capacitance (C L ) 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
Rf
Rd
Cd
25pF Cg
25pF
EXTERNAL
CRYSTAL
X1 X2
MAX6900
Figure 9. Oscillator Functional Schematic