
DS1308
Low-Current I2C RTC with 56-Byte NV RAM
7
Maxim Integrated
Pin Configuration
Pin Description
PIN
NAME
FUNCTION
1
X1
32.768kHz Crystal Connections. The internal oscillator circuitry is designed for use with a crystal
having a specified load capacitance (CL) of 6pF.
Note: For more information about crystal selection and crystal layout considerations, refer to
Application Note 58: Crystal Considerations with Maxim Real-Time Clocks (RTCs).
2
X2
3
VBAT
Battery Supply Input for Lithium Cell or Other Energy Source. Battery voltage must be held between
the minimum and maximum limits for proper operation. Diodes placed in series between the backup
source and the VBAT pin can prevent proper operation. If a backup supply is not required, VBAT
must be grounded. UL recognized to ensure against reverse charging when used with a lithium cell.
4
GND
Ground
5
SDA
Serial Data Input/Output for the I2C serial interface. It is an open-drain output and requires an
external pullup resistor. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC.
6
SCL
Serial Clock Input for the I2C serial interface. Used to synchronize data movement on the serial
interface. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC.
7
SQW/CLKIN
Square-Wave Output/Clock Input. This I/O pin is used to output one of four square-wave
frequencies (1Hz, 4kHz, 8kHz, 32kHz) or accept an external clock input to drive the RTC counter.
In the output mode (ECLK = 0), it is open drain and requires an external pullup resistor. The
square-wave operates on VCC, or on VBAT with BBCLK = 1. The pullup voltage can be up to 5.5V,
regardless of the voltage on VCC. If not used, this pin may be left unconnected.
8
VCC
Primary Power Supply. Decouple the power supply with a 0.1FF capacitor to ground.
SOP
27
SQW/CLKIN
X2
18
VCC
X1
SCL
VBAT
36
SDA
GND
45
DS1308
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