Datasheet

DS1302 Trickle-Charge Timekeeping Chip
4 of 13
PIN DESCRIPTION
PIN NAME FUNCTION
1 V
CC2
Primary Power-Supply Pin in Dual Supply Configuration. V
CC1
is connected to a
backup source to maintain the time and date in the absence of primary power. The
DS1302 operates from the larger of V
CC1
or V
CC2
. When V
CC2
is greater than V
CC1
+
0.2V, V
CC2
powers the DS1302. When V
CC2
is less than V
CC1
, V
CC1
powers the
DS1302.
2 X1
3 X2
Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator is
designed for operation with a crys
tal having a specified load capacitance of 6pF.
For more information on crystal selection and crystal layout considerations, refer to
Application Note 58: Crystal Considerations for Dallas Real-Time Clocks. The
DS1302 can also be driven by an external 32.768kHz oscillator. In this
configuration, the X1 pin is connected to the external oscillator signal and the X2 pin
is floated.
4 GND Ground
5 CE
Input. CE signal must be asserted high during a read or a write. This pin has an
internal 40kΩ (typ) pulldown resistor to groun
d. Note: Previous data sheet revisions
referred to CE as RST. The functionality of the pin has not changed.
6 I/O
Input/Push-Pull Output. The I/O pin is the bidirectional data pin for the 3-wire
interface. This pin has an i
nternal 40kΩ (typ) pulldown resistor to ground.
7 SCLK
Input. SCLK is used to synchronize data movement on the serial interface. This pin
has a
n internal 40kΩ (typ) pulldown resistor to ground.
8 V
CC1
Low-Power Operation in Single Supply and Battery-Operated Systems and Low-
Po
wer Battery Backup. In systems using the trickle charger, the rechargeable
energy source is connected to this pin. UL recognized to ensure against reverse
charging current when used with a lithium battery. Go to
www.maxim-
ic.com/TechSupport/QA/ntrl.htm.