1338-18DCGI8 IDT, Integrated Device Technology Inc, 1338-18DCGI8 Datasheet - Page 3

• Manufacturer Part Number: 1338-18DCGI8
• Manufacturer: IDT, Integrated Device Technology Inc

Specifications of 1338-18DCGI8

• Bus Type: Serial (I2C)
• User Ram: 56Byte
• Operating Supply Voltage (max): 5.5V
• Operating Temperature Classification: Industrial
• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 8
• Mounting: Surface Mount
• Date Format: DW:DM:M:Y
• Time Format: HH:MM:SS
• Lead Free Status / RoHS Status: Compliant

Typical Operating Circuit
Detailed Description
The following sections discuss in detail the Oscillator block,
Power Control block, Clock/Calendar Register Block and
Serial I
Oscillator Block
Selection of the right crystal, correct load capacitance and
careful PCB layout are important for a stable crystal
oscillator. Due to the optimization for the lowest possible
current in the design for these oscillators, losses caused by
parasitic currents can have a significant impact on the
overall oscillator performance. Extra care needs to be taken
to maintain a certain quality and cleanliness of the PCB.
Crystal Selection
The key parameters when selecting a 32 kHz crystal to work
with IDT1338 RTC are:
•
•
•
Effective Load Capacitance
Please see diagram below for effective load capacitance
calculation. The effective load capacitance (CL) should
match the recommended load capacitance of the crystal in
order for the crystal to oscillate at its specified parallel
resonant frequency with 0ppm frequency error.
IDT® REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM 3
IDT1338
REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM
Recommended Load Capacitance
Crystal Effective Series Resistance (ESR)
Frequency Tolerance
2
C block.
CPU
V
CC
2k
2k
V
CC
SDA
SCL
CRYSTAL
X1
IDT1338
In the above figure, X1 and X2 are the crystal pins of our
device. Cin1 and Cin2 are the internal capacitors which
include the X1 and X2 pin capacitance. Cex1 and Cex2 are
the external capacitors that are needed to tune the crystal
frequency. Ct1 and Ct2 are the PCB trace capacitances
between the crystal and the device pins. CS is the shunt
capacitance of the crystal (as specified in the crystal
manufacturer's datasheet or measured using a network
analyzer).
Note: IDT1338CSRI integrates a standard 32.768 kHz
crystal in the package and contributes an additional
frequency error of 10ppm at nominal
T
X2
A
=
GND
+25°C.
SQW/OUT
V
V
CC
CC
V
BAT
+
-
10k
IDT1338
V
CC
(+3.3 V) and
REV K 032910
RTC