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.
MAX6902
SPI-Compatible RTC in a TDFN
4 _______________________________________________________________________________________
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.
6V
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
—EP
Exposed Paddle. Internally connected to
GND. Connect to GND, but do not use as
the sole ground connection point or leave
unconnected.
PARAMETER SYMBOL MIN TYP MAX UNITS
Frequency f 32.768 kHz
Equivalent
Series
Resistance
(ESR)
R
S
40 60 kΩ
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
Table 1. Acceptable Quartz Crystal
Parameters
0.1
1.0
10.0
TIMEKEEPING CURRENT
vs. SUPPLY VOLTAGE
MAX6902 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (μA)
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5
Typical Operating Characteristic
(T
A
= +25°C, unless otherwise noted.)
