Rainbow Electronics MAX6902 - Manual (Page 4)

MAX6902
Detailed Description
The MAX6902 is a real-time clock/calendar with an SPI-
compatible interface and 31 x 8 bits of SRAM. It pro-
vides seconds, minutes, hours, day of the week, date of
the month, month, and year information, held in seven 8-
bit timekeeping registers (Functional Diagram). An on-
chip 32.768kHz oscillator circuit requires only a single
external crystal to operate. Table 1 specifies the para-
meters for the external crystal, and Figure 1 shows a
functional schematic of the oscillator circuit. The
MAX6902’s register addresses and definitions are
described in Figure 2 and in Table 2. Time and calendar
data are stored in the registers in binary-coded decimal
(BCD) format. A polled alarm function is included for
scheduled timing of user-defined times or intervals.
Table 1. Acceptable Quartz Crystal
Parameters
SPI-Compatible RTC in a TDFN
4 _______________________________________________________________________________________
0.1
1.0
10.0
TIMEKEEPING CURRENT
vs. SUPPLY VOLTAGE
MAX6902 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
µ
A)
2.0 3.5 4.0 2.5 3.0 4.5 5.0 5.5
Typical Operating Characteristics
(T A = +25°C, unless otherwise noted.)
Pin Description
PIN NAME FUNCTION
1 SCLK
Serial Clock Input. SPI clock for DIN and
DOUT data transfers.
2 DOUT SPI Data Output
3 DIN SPI Data Input
4 GND Ground
5 CS
Chip Select Input. Active low for valid data
transfers.
6 V CC
Power-Supply Pin. Bypass V
CC
to GND
with a 0.1µF capacitor.
7 X2 External 32.768kHz Crystal
8 X1 External 32.768kHz Crystal
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
MAX6902
X1 X2
25pF 25pF
EXTERNAL
CRYSTAL
Figure 1. Crystal Oscillator Circuit Schematic