DS1338_11 Datasheet, PDF (7/16 Pages) Maxim Integrated Products – I2C RTC with 56-Byte NV RAM

DS1338 I²C RTC with 56-Byte NV RAM
PIN DESCRIPTION
PIN
8
16
NAME
1
—
X1
2
—
X2
3
14
V_BAT
4
15
GND
5
16
6
1
SDA
SCL
7
2
SQW/OUT
8
3
V_CC
FUNCTION
32.768kHz Crystal Connections. The internal oscillator circuitry is designed for
operation with a crystal having a specified load capacitance (C_L) of 12.5pF. An
external 32.768kHz oscillator can also drive the DS1338. In this configuration,
the X1 pin is connected to the external oscillator signal and the X2 pin is left
unconnected.
Note: For more information about crystal selection and crystal layout considerations,
refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks.
Backup 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 V_BAT pin may
prevent proper operation. If a backup supply is not required, V_BAT must be
grounded. UL recognized to ensure against reverse charging when used with a
lithium cell. For more information, visit www.maxim-ic.com/qa/info/ul.
Ground. DC power is provided to the device on these pins. V_CC is the primary
power input. When voltage is applied within normal limits, the device is fully
accessible and data can be written and read. When a backup supply is
connected to the device and V_CC is below V_PF, reads and writes are inhibited.
However, the timekeeping function continues unaffected by the lower input
voltage.
Serial Data. Input/output pin for the I²C serial interface. It is an open drain
output and requires an external pullup resistor. The pull up voltage may be up
to 5.5V regardless of the voltage on V_CC.
Serial Clock. Input pin for the I²C serial interface. Used to synchronize data
movement on the serial interface. The pull up voltage may be up to 5.5V
regardless of the voltage on V_CC.
Square-Wave/Output Driver. When enabled and the SQWE bit set to 1, the
SQW/OUT pin outputs one of four square-wave frequencies (1Hz, 4kHz, 8kHz,
32kHz). It is an open drain output and requires an external pullup resistor.
Operates with either V_CC or V_BAT applied. The pull up voltage may be up to
5.5V regardless of the voltage on V_CC. If not used, this pin may be left
unconnected.
Primary Power Supply. When voltage is applied within normal limits, the device
is fully accessible and data can be written and read. When a backup supply is
connected to the device and V_CC is below V_PF, reads and writes are inhibited.
The backup supply maintains the timekeeping function while V_CC is absent.
— 4–13
N.C.
No Connection. These pins are not connected internally, but must be grounded
for proper operation.
DETAILED DESCRIPTION
The DS1338 serial RTC is a low-power, full BCD clock/calendar plus 56 bytes of NV SRAM. Address and data are
transferred serially through an I²C interface. The clock/calendar provides seconds, minutes, hours, day, date,
month, and year information. The end of the month date is automatically adjusted for months with fewer than 31
days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM
indicator. The DS1338 has a built-in power-sense circuit that detects power failures and automatically switches to
the V_BAT supply.
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