User Manual

MAX6901
32.768kHz Output (32KHZ)
32KHZ is a push-pull 32.768kHz output for timing or
clocking of external devices. Bit D7 in the Clock
Seconds register is the active-low enable bit for 32KHZ.
When D7 is logic 0, 32KHZ is enabled. When logic 1,
32KHZ is disabled and set to high impedance. Power-
on reset enables the 32.768kHz output.
Applications Information
Crystal Selection
The MAX6901 is designed to use a standard 32.768kHz
watch crystal. Table 1 details the recommended crystal
requirements. Some suggested crystals are listed in
Table 4. In addition to the specified SMT devices, some
of the listed manufacturers also offer other package
options.
Frequency Stability and Temperature
Timekeeping accuracy of the MAX6901 is dependent
on the frequency stability of the external crystal. To
determine frequency stability, use the parabolic curve
in Figure 6 and the following equations:
∆f = fk (T
0
- T)
2
where:
∆f = change in frequency from +25°C
3-Wire Serial RTC in a TDFN
12 ______________________________________________________________________________________
Figure 2. Single Byte Data Transfer
SCLK
A0
A1 A2 A3 A4 A5 A6 A7
D0 D1 D2 D3 D4 D5 D6 D7
CS
I/O
ADDRESS/COMMAND BYTE
I/O DATA BYTE
11A1 A2 A3 A4 A5 R
R = RAM/ REGISTER SELECT BIT
RAM = 1, REGISTER = 0
ADDRESS/COMMAND BYTE
(b) 3-WIRE SINGLE BYTE WRITE:
(a) 3-WIRE SINGLE BYTE READ:
I/O DATA BYTE
A1 A2 A3 A4 A5 A6 A7 D0 D1 D2 D3 D4 D5 D6
CS
SCLK
I/O
D7
0 A1 A2 A3 A4 A5 R 1
R = RAM/ REGISTER SELECT BIT
RAM = 1, REGISTER = 0