DATASHEET
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE IDT1337G
IDT®
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General Description
The IDT1337G device is a low power serial real-time clock
(RTC) device with two programmable time-of-day alarms
and a programmable square-wave output. Address and
data are transferred serially through an I2C bus. The device
provides seconds, minutes, hours, day, date, month, and
year information. The date at the end of the month 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.
Applications
•Telecommunication (Routers, Switches, Servers)
•Handhelds (GPS, POS terminals, MP3 players)
•Set-Top Box, Digital Recording,
•Office (Fax/Printers, Copiers)
•Medical (Glucometer, Medicine Dispensers)
•Other (Thermostats, Vending Machines, Modems, Utility
Meters, Digital Photo Frame devices)
Features
•Real-Time Clock (RTC) counts seconds, minutes, hours,
day, date, month, and year with leap-year compensation
valid up to 2100
•Packaged in 8-pin MSOP, 8-pin SOIC, 16-pin QFN
(without integrated crystal), or 16-pin SOIC
(surface-mount package with an integrated crystal)
•I2C Serial interface (Normal and Fast modes)
•Two time-of-day alarms
•Oscillator Stop Flag
•Programmable square-wave output defaults to 32 kHz on
power-up
•Operating voltage of 1.8 to 5.5 V
•Industrial temperature range (-40 to +85°C)
•Extended temperature range (-40 to +105°C) for 8-pin
SOIC package
Block Diagram
SCL
SDA
Crystal in sid e pa cka ge
for 16-pin SOIC ONLY
X1
X2
1 Hz/4.096 kHz/
8.192 kHz/32.768 kHz SQW/INTB
I2C
Interface
32.768 kHz
Oscillator and
Divider
Control
Logic
MUX/
Buffer
Clock,
Calendar
Counter
1 Byte
Control 7 Bytes
Buffer Alarm
Registers
INTA
VCC
GND
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Pin Assignment (8-pin MSOP/SOIC)
Pin Assignment (16-pin SOIC)
Pin Assignment (16-pin QFN)
X1
INTA SCL
SQW/INTB
GND
VCC1
2
3
4
8
7
6
5SDA
X2
IDT1337G
16
1
15
2
14
3
13
4
5
6
7
89
10
12
11
SCL
VCC
NC
NC
NC
NC
NC NC
NC
NC
NC
NC
SDA
GND
INTA
SQW/INTB
IDT1337G
1
59
13
NC
INTA
GND
NC
SDA
NC
NC
SCL NC
X1
X2
NC
NC
VCC
SQW/INTB
NC
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Pin Descriptions
Pin Number Pin
Name Pin Description/Function
MSOP SOIC QFN
1 — 14 X1 Connections for standard 32.768 kHz quartz crystal. The internal oscillator
circuitry is designed for operation with a crystal having a specified load
capacitance (CL) of 7 pF. An external 32.768 kHz oscillator can also drive the
IDT1337G. In this configuration, the X1 pin is connected to the external
oscillator signal and the X2 pin is left floating.
2—15 X2
314 2 INTA
Interrupt output. When enabled, INTA is asserted low when the time/day/date
matches the values set in the alarm registers. This pin is an open-drain output
and requires an external pull-up resistor (10 k typical).
4 15 3 GND Connect to ground. DC power is provided to the device on these pins.
5 16 6 SDA Serial data input/output. SDA is the input/output pin for the I2C serial interface.
The SDA pin is an open-drain output and requires an external pull-up resistor
(2 k typical).
6 1 7 SCL Serial clock input. SCL is used to synchronize data movement on the serial
interface. The SCL pin is an open-drain output and requires an external pull-up
resistor (2 k typical).
7 2 10 SQW/INTB
Square-Wave/Interrupt output. Programmable square-wave or interrupt output
signal. The SQW/INT pin is an open-drain output and requires an external
pull-up resistor (10 k typical). This pin can also function as an additional
interrupt pin under certain conditions (see page 6 for details).
8 3 11 VCC Primary power supply. DC power is applied to this pin.
— 4 - 13 1,4,5,8,9,
12,13,16
NC No connect. These pins are unused and must be connected to ground.
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Typical Operating Circuit
Detailed Description
Communications to and from the IDT1337G occur serially
over an I2C bus. The IDT1337G operates as a slave device
on the serial bus. Access is obtained by implementing a
START condition and providing a device identification code,
followed by data. Subsequent registers can be accessed
sequentially until a STOP condition is executed. The device
is fully accessible through the I2C interface whenever VCC
is between 5.5 V and 1.8 V. I2C operation is not guaranteed
when VCC is below 1.8 V. The IDT1337G maintains the time
and date when VCC is as low as 1.3 V.
The following sections discuss in detail the Oscillator block,
Clock/Calendar Register Block and Serial I2C block.
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 IDT1337G RTC are:
•Recommended Load Capacitance
•Crystal Effective Series Resistance (ESR)
•Frequency Tolerance
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.
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).
CPU
X1 X2 VCC
SQW/INTB
INTA
GND
SDA
SCL
CRYSTAL
IDT1337G
VCC
2k
2k
VCC
VCC
10k 10k
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Note: IDT1337CSRI integrates a standard 32.768 kHz
crystal in the package and contributes an additional
frequency error of 10ppm at nominal VCC (+3.3 V) and
TA=+25°C.
ESR (Effective Series Resistance)
Choose the crystal with lower ESR. A low ESR helps the
crystal to start up and stabilize to the correct output
frequency faster compared to high ESR crystals.
Frequency Tolerance
The frequency tolerance for 32 KHz crystals should be
specified at nominal temperature (+25°C) on the crystal
manufacturer datasheet. The crystals used with IDT1337G
typically have a frequency tolerance of +/-20ppm at +25°C.
Specifications for a typical 32 kHz crystal used with our
device are shown in the table below.
PCB Design Consideration
•Signal traces between IDT device pins and the crystal
must be kept as short as possible. This minimizes
parasitic capacitance and sensitivity to crosstalk and
EMI. Note that the trace capacitances play a role in the
effective crystal load capacitance calculation.
•Data lines and frequently switching signal lines should be
routed as far away from the crystal connections as
possible. Crosstalk from these signals may disturb the
oscillator signal.
•Reduce the parasitic capacitance between X1 and X2
signals by routing them as far apart as possible.
•The oscillation loop current flows between the crystal and
the load capacitors. This signal path (crystal to CL1 to
CL2 to crystal) should be kept as short as possible and
ideally be symmetric. The ground connections for both
capacitors should be as close together as possible.
Never route the ground connection between the
capacitors all around the crystal, because this long
ground trace is sensitive to crosstalk and EMI.
•To reduce the radiation / coupling from oscillator circuit,
an isolated ground island on the GND layer could be
made. This ground island can be connected at one point
to the GND layer. This helps to keep noise generated by
the oscillator circuit locally on this separated island. The
ground connections for the load capacitors and the
oscillator should be connected to this island.
PCB Layout
PCB Assembly, Soldering and Cleaning
Board-assembly production process and assembly quality
can affect the performance of the 32 KHz oscillator.
Depending on the flux material used, the soldering process
can leave critical residues on the PCB surface. High
humidity and fast temperature cycles that cause humidity
condensation on the printed circuit board can create
process residuals. These process residuals cause the
insulation of the sensitive oscillator signal lines towards
each other and neighboring signals on the PCB to decrease.
High humidity can lead to moisture condensation on the
surface of the PCB and, together with process residuals,
reduce the surface resistivity of the board. Flux residuals on
the board can cause leakage current paths, especially in
humid environments. Thorough PCB cleaning is therefore
highly recommended in order to achieve maximum
performance by removing flux residuals from the board after
assembly. In general, reduction of losses in the oscillator
circuit leads to better safety margin and reliability.
Parameter Symbol Min Typ Max Units
Nominal Freq. fO32.768 kHz
Series Resistance ESR 80 k
Load Capacitance CL7pF
1337G
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Address Map
Table 2 (Timekeeper Registers) shows the address map for the IDT1337G registers. During a multibyte access, when the
address pointer reaches the end of the register space (0Fh), it wraps around to location 00h. On an I2C START, STOP, or
address pointer incrementing to location 00h, the current time is transferred to a second set of registers. The time
information is read from these secondary registers, while the clock may continue to run. This eliminates the need to re-read
the registers in case of an update of the main registers during a read.
Table 1. Timekeeper Registers
Note: Unless otherwise specified, the state of the registers are not defined when power is first applied or when VCC falls below the VCCT
min
Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Function Range
00h 0 10 seconds Seconds Seconds 00 - 59
01h 0 10 minutes Minutes Minutes 00 - 59
02h 0 12/24
AM/PM
10 hour Hour Hours
1 - 12 +
AM/PM
00 - 23
10 hour
03h00000 Day Day 1 - 7
04h 0 0 10 date Date Date 01 - 31
05h Century 0 0 10 month Month Month/Century 01 - 12 +
Century
06h 10 year Year Year 00 - 99
07h A1M1 10 seconds Seconds Alarm 1
Seconds
00 - 59
08h A1M2 10 minutes Minutes Alarm 1
Minutes
00 - 59
09h A1M3 12/24
AM/PM
10 hour Hour Alarm 1 Hours
1 - 12 +
AM/PM
00 - 23
10 hour
0Ah A1M4 DY/DT 10 date Day, Alarm 1 Day 1 - 7
Date Alarm 1 Date 1 - 31
0Bh A2M2 10 minutes Minutes Alarm 2
Minutes
00 - 59
0Ch A2M3 12/24
AM/PM
10 hour Hour Alarm 2 Hours
1 - 12 +
AM/PM
00 - 23
10 hour
0Dh A2M4 DY/DT 10 date Day, Alarm 2 Day 1 - 7
Date Alarm 2 Date 1 - 31
0Eh EOSC 0 0 RS2 RS1 INTCN A2IE A1IE Control
0FhOSF00000A2FA1FStatus
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Clock and Calendar
The time and calendar information is obtained by reading
the appropriate register bytes. The RTC registers are
illustrated in Table 1. The time and calendar are set or
initialized by writing the appropriate register bytes. The
contents of the time and calendar registers are in the
binary-coded decimal (BCD) format.
The day-of-week register increments at midnight. Values
that correspond to the day of week are user-defined but
must be sequential (i.e., if 1 equals Sunday, then 2 equals
Monday, and so on). Illogical time and date entries result in
undefined operation.
When reading or writing the time and date registers,
secondary (user) buffers are used to prevent errors when
the internal registers update. When reading the time and
date registers, the user buffers are synchronized to the
internal registers on any start or stop and when the register
pointer rolls over to zero.
The countdown chain is reset whenever the seconds
register is written. Write transfers occur on the acknowledge
pulse from the device. To avoid rollover issues, once the
countdown chain is reset, the remaining time and date
registers must be written within 1 second. The 1Hz
square-wave output, if enable, transitions high 500ms after
the seconds data transfer, provided the oscillator is already
running.
The IDT1337G can be run in either 12-hour or 24-hour
mode. Bit 6 of the hours register is defined as the 12- or
24-hour mode-select bit. When high, the 12-hour mode is
selected. In the 12-hour mode, bit 5 is the AM/PM bit with
logic high being PM. In the 24-hour mode, bit 5 is the second
10-hour bit (20–23 hours). All hours values, including the
alarms, must be reinitialized whenever the 12/24-hour mode
bit is changed. The century bit (bit 7 of the month register)
is toggled when the years register overflows from 99–00.
Alarms
The IDT1337G contains two time of day/date alarms. Alarm
1 can be set by writing to registers 07h to 0Ah. Alarm 2 can
be set by writing to registers 0Bh to 0Dh. The alarms can be
programmed (by the INTCN bits of the Control Register) to
operate in two different modes—each alarm can drive its
own separate interrupt output or both alarms can drive a
common interrupt output. Bit 7 of each of the
time-of-day/date alarm registers are mask bits (Table 1).
When all of the mask bits for each alarm are logic 0, an
alarm only occurs when the values in the timekeeping
registers 00h–06h match the values stored in the
time-of-day/date alarm registers. The alarms can also be
programmed to repeat every second, minute, hour, day, or
date. Table 2 (Alarm Mask Bits table) shows the possible
settings. Configurations not listed in the table result in
illogical operation
The DY/DT bits (bit 6 of the alarm day/date registers) control
whether the alarm value stored in bits 0 to 5 of that register
reflects the day of the week or the date of the month. If
DY/DT is written to a logic 0, the alarm is the result of a
match with date of the month. If DY/DT is written to a logic
1, the alarm is the result of a match with day of the week.
When the RTC register values match alarm register
settings, the corresponding Alarm Flag (‘A1F’ or ‘A2F’) bit is
set to logic 1. If the corresponding Alarm Interrupt Enable
(‘A1IE’ or ‘A2IE’) is also set to logic 1, the alarm condition
activates one of the interrupt output (INTA or SQW/INTB)
signals. The match is tested on the once-per-second update
of the time and date registers.
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Table 2. Alarm Mask Bits
Special-Purpose Registers
The IDT1337G has two additional registers (control and status) that control the RTC, alarms, and square-wave output.
Control Register (0Eh)
Bit 7: Enable Oscillator (EOSC). This active-low bit when set to logic 0 starts the oscillator. When this bit is set to
a logic 1, the oscillator is stopped. This bit is enabled (logic 0) when power is first applied.
Bits 4 and 3: Rate Select (RS2 and RS1). These bits control the frequency of the square-wave output when the
square wave has been enabled. Table 3 shows the square-wave frequencies that can be selected with the RS bits.
These bits are both set to logic 1 (32 kHz) when power is first applied.
Table 3. SQW/INT Output
DY/DT Alarm 1 Register Mask Bits (Bit 7) Alarm Rate
A1M4 A1M3 A1M2 A1M1
X1111Alarm once per second.
X1110Alarm when seconds match.
X1100Alarm when minutes and seconds match.
X1000Alarm when hours, minutes, and seconds match.
00000Alarm when date, hours, minutes, and seconds match.
10000Alarm when day, hours, minutes, and seconds match.
DY/DT Alarm 2 Register Mask Bits (Bit 7) Alarm Rate
A2M4 A2M3 A2M2
X 1 1 1 Alarm once per minute (00 seconds of every minute).
X 1 1 0 Alarm when minutes match.
X 1 0 0 Alarm when hours and minutes match.
0 0 0 0 Alarm when date, hours, and minutes match.
1 0 0 0 Alarm when day, hours, and minutes match.
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
EOSC 0 0 RS2 RS1 INTCN A2IE A1IE
INTCN RS2 RS1 SQW/INTB Output A2IE
000 1 Hz X
0 0 1 4.096 kHz X
0 1 0 8.192 kHz X
0 1 1 32.768 kHz X
1XX A2F 1
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Bit 2: Interrupt Control (INTCN). This bit controls the relationship between the two alarms and the interrupt output
pins. When the INTCN bit is set to logic 1, a match between the timekeeping registers and the alarm 1 registers
activate the INTA pin (provided that the alarm is enabled) and a match between the timekeeping registers and the
alarm 2 registers activates the SQW/INTB pin (provided that the alarm is enabled). When the INTCN bit is set to
logic 0, a square wave is output on the SQW/INTB pin and alarm 2 registers activates the INTA pin (provided that
the alarm is enabled). Alarm 1 registers have no effect on the INTA pin.This bit is set to logic 0 when power is first
applied.
Bit 1: Alarm 2 Interrupt Enable (A2IE). When set to a logic 1, this bit permits the Alarm 2 Flag (A2F) bit in the
status register to assert INTA (when INTCN = 0) or to assert SQW/INTB (when INTCN = 1). When the A2IE bit is
set to logic 0, the A2F bit does not initiate an interrupt signal. The A2IE bit is disabled (logic 0) when power is first
applied.
Bit 0: Alarm 1 Interrupt Enable (A1IE). When set to logic 1, this bit permits the Alarm 1 Flag (A1F) bit in the status
register to assert INTA (when INTCN = 1). It does not assert any interrupt pins when INTCN=0. When the A1IE bit
is set to logic 0, the A1F bit does not initiate the INTA signal. The A1IE bit is disabled (logic 0) when power is first
applied.
Table 4. Alarm/Interrupt Table
Bit 2 Bit 1 Bit 0
INTCN A2IE A1IE Alarm 1 Alarm 2 INTA INTB/SQW
0 0 0 None None Hi Square Wave
0 0 1 None None Hi Square Wave
0 1 0 None INTA Alarm 2 Square Wave
0 1 1 None INTA Alarm 2 Square Wave
100 None None Hi Hi
101 INTA None Alarm 1 Hi
110 None INTB Hi Alarm 2
1 1 1 INTA INTB Alarm 1 Alarm 2
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Status Register (0Fh)
Bit 7: Oscillator Stop Flag (OSF). A logic 1 in this bit indicates that the oscillator either is stopped or was stopped
for some period of time and may be used to judge the validity of the clock and calendar data. This bit is set to logic
1 anytime the oscillator stops. The following are examples of conditions that can cause the OSF bit to be set:
1) The first time power is applied.
2) The voltage present on VCC is insufficient to support oscillation.
3) The EOSC bit is turned off.
4) External influences on the crystal (e.g., noise, leakage, etc.).
This bit remains at logic 1 until written to logic 0. This bit can only be written to a logic 0.
Bit 1: Alarm 2 Flag (A2F). A logic 1 in the alarm 2 flag bit indicates that the time matched the alarm 2 registers.
This flag can be used to generate an interrupt on either INTA or SQW/INTB depending on the status of the INTCN
bit in the control register. If the INTCN bit is set to logic 0 and A2F is at logic 1 (and A2IE bit is also logic 1), the INTA
pin goes low. If the INTCN bit is set to logic 1 and A2F is logic 1 (and A2IE bit is also logic 1), the SQW/INTB pin
goes low. A2F is cleared when written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1
leaves the value unchanged.
Bit 0: Alarm 1 Flag (A1F). A logic 1 in the Alarm 1 Flag bit indicates that the time matched the alarm 1 registers. If
the A1IE bit is also a logic 1, the INTA pin goes low. A1F is cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write to logic 1 leaves the value unchanged.
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
OSF00000A2FA1F
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I2C Serial Data Bus
The IDT1337G supports the I2C bus protocol. A device that
sends data onto the bus is defined as a transmitter and a
device receiving data as a receiver. The device that controls
the message is called a master. The devices that are
controlled by the master are referred to as slaves. A master
device that generates the serial clock (SCL), controls the
bus access, and generates the START and STOP conditions
must control the bus. The IDT1337G operates as a slave on
the I2C bus. Within the bus specifications, a standard mode
(100 kHz maximum clock rate) and a fast mode (400 kHz
maximum clock rate) are defined. The IDT1337G works in
both modes. Connections to the bus are made via the
open-drain I/O lines SDA and SCL.
The following bus protocol has been defined (see the “Data
Transfer on I2C Serial Bus” figure):
•Data transfer may be initiated only when the bus is not
busy.
•During data transfer, the data line must remain stable
whenever the clock line is HIGH. Changes in the data line
while the clock line is HIGH are interpreted as control
signals.
Accordingly, the following bus conditions have been defined:
Bus not busy: Both data and clock lines remain HIGH.
Start data transfer: A change in the state of the data line,
from HIGH to LOW, while the clock is HIGH, defines a
START condition.
Stop data transfer: A change in the state of the data line,
from LOW to HIGH, while the clock line is HIGH, defines the
STOP condition.
Data valid: The state of the data line represents valid data
when, after a START condition, the data line is stable for the
duration of the HIGH period of the clock signal. The data on
the line must be changed during the LOW period of the clock
signal. There is one clock pulse per bit of data.
Each data transfer is initiated with a START condition and
terminated with a STOP condition. The number of data
bytes transferred between START and STOP conditions are
not limited, and are determined by the master device. The
information is transferred byte-wise and each receiver
acknowledges with a ninth bit.
Acknowledge: Each receiving device, when addressed, is
obliged to generate an acknowledge after the reception of
each byte. The master device must generate an extra clock
pulse that is associated with this acknowledge bit.
A device that acknowledges must pull down the SDA line
during the acknowledge clock pulse in such a way that the
SDA line is stable LOW during the HIGH period of the
acknowledge related clock pulse. Of course, setup and hold
times must be taken into account. A master must signal an
end of data to the slave by not generating an acknowledge
bit on the last byte that has been clocked out of the slave. In
this case, the slave must leave the data line HIGH to enable
the master to generate the STOP condition.
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Data Transfer on I2C Serial Bus
Depending upon the state of the R/W bit, two types of data
transfer are possible:
1) Data transfer from a master transmitter to a slave
receiver. The first byte transmitted by the master is the
slave address. Next follows a number of data bytes. The
slave returns an acknowledge bit after each received byte.
Data is transferred with the most significant bit (MSB) first.
2) Data transfer from a slave transmitter to a master
receiver. The first byte (the slave address) is transmitted by
the master. The slave then returns an acknowledge bit,
followed by the slave transmitting a number of data bytes.
The master returns an acknowledge bit after all received
bytes other than the last byte. At the end of the last received
byte, a “not acknowledge” is returned. The master device
generates all of the serial clock pulses and the START and
STOP conditions. A transfer is ended with a STOP condition
or with a repeated START condition. Since a repeated
START condition is also the beginning of the next serial
transfer, the bus is not released. Data is transferred with the
most significant bit (MSB) first.
The IDT1337G can operate in the following two modes:
1) Slave Receiver Mode (Write Mode): Serial data and
clock are received through SDA and SCL. After each byte is
received an acknowledge bit is transmitted. START and
STOP conditions are recognized as the beginning and end
of a serial transfer. Address recognition is performed by
hardware after reception of the slave address and direction
bit (see the “Data Write–Slave Receiver Mode” figure). The
slave address byte is the first byte received after the START
condition is generated by the master. The slave address
byte contains the 7-bit IDT1337G address, which is
1101000, followed by the direction bit (R/W), which is 0 for a
write. After receiving and decoding the slave address byte
the device outputs an acknowledge on the SDA line. After
the IDT1337G acknowledges the slave address + write bit,
the master transmits a register address to the IDT1337G.
This sets the register pointer on the IDT1337G. The master
may then transmit zero or more bytes of data, with the
IDT1337G acknowledging each byte received. The address
pointer increments after each data byte is transferred. The
master generates a STOP condition to terminate the data
write.
2) Slave Transmitter Mode (Read Mode): The first byte is
received and handled as in the slave receiver mode.
However, in this mode, the direction bit indicates that the
transfer direction is reversed. Serial data is transmitted on
SDA by the IDT1337G while the serial clock is input on SCL.
START and STOP conditions are recognized as the
beginning and end of a serial transfer (see the “Data
Read–Slave Transmitter Mode” figure). The slave address
byte is the first byte received after the START condition is
generated by the master. The slave address byte contains
the 7-bit IDT1337G address, which is 1101000, followed by
the direction bit (R/W), which is 1 for a read. After receiving
and decoding the slave address byte the slave outputs an
acknowledge on the SDA line. The IDT1337G then begins
to transmit data starting with the register address pointed to
by the register pointer. If the register pointer is not written to
before the initiation of a read mode the first address that is
read is the last one stored in the register pointer. The
IDT1337G must receive a “not acknowledge” to end a read.
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REAL-TIME CLOCK WITH I
2
C SERIAL INTERFACE 13
IDT1337G REV L 062613
Data Write – Slave Receiver Mode
Data Read (from current Pointer location) – Slave Transmitter Mode
Data Read (Write Pointer, then Read) – Slave Receive and Transmit
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Handling, PCB Layout, and Assembly
The IDT1337G package contains a quartz tuning-fork crystal. Pick-and-place equipment may be used, but precautions
should be taken to ensure that excessive shocks are avioded. Ultrasonic cleaning equipment should be avioded to prevent
damage to the crystal.
Avoid running signal traces under the package, unless a ground plane is placed between the package and the signal line.
All NC (no connect) pins must be connected to ground.
Moisture-sensitive packages are shipped from the factory dry-packed. Handling instructions listed on the package label must
be followed to prevent damage during reflow. Refer to the IPC/JEDEC J-STD-020 standard for moisture-sensitive device
(MSD) classifications.
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the IDT1337G. These ratings, which are
standard values for IDT commercially rated parts, are stress ratings only. Functional operation of the device at these
or any other conditions above those indicated in the operational sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods can affect product reliability. Electrical
parameters are guaranteed only over the recommended operating temperature range.
Recommended DC Operating Conditions
Item Rating
Voltage Range (on any pin relative to ground) -0.3 V to +6.0 V
Storage Temperature -55 to +125C
Soldering Temperature 260C
Ambient Operating Temperature (industrial) -40 to +85°C
Ambient Operating Temperature (extended) -40 to +105°C
Parameter Symbol Conditions Min. Typ. Max. Units
VCC Supply Voltage VCC Full operation 1.8 3.3 5.5 V
VCCT Timekeeping 1.3 1.8 V
Ambient Operating Temperature (industrial) TA-40 +85 C
Ambient Operating Temperature (extended) TA-40 +105 C
Logic 1 VIH SCL, SDA 0.8VCC VCC + 0.3 V
INTA, SQW/INTB 5.5
Logic 0 VIL -0.3 +0.3VCC V
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
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DC Electrical Characteristics
Unless stated otherwise, VCC = 1.8 V to 5.5 V, Ambient Temp. -40 to +85C and -40 to +105°C (extended), Note 1
DC Electrical Characteristics
Unless stated otherwise, VCC = 1.3 V to 1.8 V, Ambient Temp. -40 to +85C (industrial), Note 1
Unless stated otherwise, VCC = 1.3 V to 1.8 V, Ambient Temp. -40 to +105C (extended), Note 1
Parameter Symbol Conditions Min. Typ. Max. Units
Input Leakage ILI Note 2 -1 +1 µA
I/O Leakage ILO Note 3 -1 +1 µA
Logic 0 Output
VOL = 0.4 V
IOL Note 3 3 mA
Active Supply Current ICCA Note 4 5 150 µA
Standby Current ICCS Notes 5, 6 1.5 µA
Parameter Symbol Conditions Min. Typ. Max. Units
Timekeeper Current (Oscillator
Enabled)
ICCTOSC Notes 5, 7, 8, 9 725 900 nA
Data-Retention Current (Oscillator
Disabled)
ICCTDDR Notes 5, 9 300 nA
Parameter Symbol Conditions Min. Typ. Max. Units
Timekeeper Current (Oscillator
Enabled)
ICCTOSC Notes 5, 7, 8, 9 600 1500 nA
Data-Retention Current (Oscillator
Disabled)
ICCTDDR Notes 5, 9 100 250 nA
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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IDT1337G REV L 062613
AC Electrical Characteristics
Unless stated otherwise, VCC = 1.8 V to 5.5 V, Ambient Temp. -40 to +85C and -40 to +105°C (extended), Note 1
Parameter Symbol Conditions Min. Typ. Max. Units
SCL Clock Frequency fSCL Fast Mode 100 400 kHz
Standard Mode 0 100
Bus Free Time Between a STOP and
START Condition
tBUF Fast Mode 1.3 µs
Standard Mode 4.7
Hold Time (Repeated) START
Condition, Note 10
tHD:STA Fast Mode 0.6 µs
Standard Mode 4.0
Low Period of SCL Clock tLOW Fast Mode 1.3 µs
Standard Mode 4.7
High Period of SCL Clock tHIGH Fast Mode 0.6 µs
Standard Mode 4.0
Setup Time for a Repeated START
Condition
tSU:STA Fast Mode 0.6 µs
Standard Mode 4.7
Data Hold Time, Notes 11, 12 tHD:DAT Fast Mode 0 0.9 µs
Standard Mode 0
Data Setup Time, Note 13 tSU:DAT Fast Mode 100 ns
Standard Mode 250
Rise Time of Both SDA and SCL
Signals, Note 14
tRFast Mode 20 + 0.1CB300 ns
Standard Mode 1000
Fall Time of Both SDA and SCL Signals,
Note 14
tFFast Mode 20 + 0.1CB300 ns
Standard Mode 300
Setup Time for STOP Condition tSU:STO Fast Mode 0.6 µs
Standard Mode 4.0
Capacitive Load for Each Bus Line,
Note 14
CB400 pF
I/O Capacitance (SDA, SCL) CI/O Note 15 10 pF
32.768 kHz Clock Accuracy with
External Crystal
TA=25°C
VCC=3.3 V
±10 ppm
32.768 kHz Clock Accuracy with
Internal Crystal
TA=25°C
VCC=3.3 V
(crystal accuracy
±20ppm)
±30 ppm
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
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REAL-TIME CLOCK WITH I
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Note 1: Limits at -40°C are guaranteed by design and are not production tested.
Note 2: SCL only.
Note 3: SDA, INTA, and SQW/INTB.
Note 4: ICCA—SCL clocking at maximum frequency = 400 kHz, VIL = 0.0V, VIH = VCC.
Note 5: Specified with the I2C bus inactive, VIL = 0.0V, VIH = VCC.
Note 6: SQW enabled.
Note 7: Specified with the SQW function disabled by setting INTCN = 1.
Note 8: Using recommended crystal on X1 and X2.
Note 9: The device is fully accessible when 1.8 < VCC < 5.5 V. Time and date are maintained when 1.3 V < VCC <
1.8 V.
Note 10: After this period, the first clock pulse is generated.
Note 11: A device must internally provide a hold time of at least 300 ns for the SDA signal (referred to the VIHMIN of
the SCL signal) to bridge the undefined region of the falling edge of SCL.
Note 12: The maximum tHD:DAT need only be met if the device does not stretch the LOW period (tLOW) of the SCL
signal.
Note 13: A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT > to 250 ns must
then be met. This is automatically the case if the device does not stretch the LOW period of the SCL signal. If such
a device does stretch the LOW period of the SCL signal, it must output the next data bit to the SDA line tR(MAX) +
tSU:DAT = 1000 + 250 = 1250 ns before the SCL line is released.
Note 14: CB—total capacitance of one bus line in pF.
Note 15: Guaranteed by design. Not production tested.
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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REAL-TIME CLOCK WITH I
2
C SERIAL INTERFACE 18
IDT1337G REV L 062613
Timing Diagram
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Typical Operating Characteristics
Oscillator Frequency vs Vcc
(as measured on one IDT1337C sample)
32768.3
32768.32
32768.34
32768.36
32768.38
32768.4
1.3 2.3 3.3 4.3 5.3
Vcc(V)
Frequency (Hz)
Freq
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Thermal Characteristics for 8SOIC
Thermal Characteristics for 8MSOP
Thermal Characteristics for 16SOIC
Thermal Characteristics for 16-pin QFN
Parameter Symbol Conditions Min. Typ. Max. Units
Thermal Resistance Junction to
Ambient
JA Still air 150 C/W
JA 1 m/s air flow 140 C/W
JA 3 m/s air flow 120 C/W
Thermal Resistance Junction to Case JC 40 C/W
Parameter Symbol Conditions Min. Typ. Max. Units
Thermal Resistance Junction to
Ambient
JA Still air 95 C/W
Thermal Resistance Junction to Case JC 48 C/W
Parameter Symbol Conditions Min. Typ. Max. Units
Thermal Resistance Junction to
Ambient
JA Still air 120 C/W
JA 1 m/s air flow 115 C/W
JA 3 m/s air flow 105 C/W
Thermal Resistance Junction to Case JC 58 C/W
Parameter Symbol Conditions Min. Typ. Max. Units
Thermal Resistance Junction to
Ambient
JA Still air 69.4 C/W
JA 1 m/s air flow 60.7 C/W
JA 2.5 m/s air flow 54.4 C/W
Thermal Resistance Junction to Case JC 9.7 C/W
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
IDT®
REAL-TIME CLOCK WITH I
2
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IDT1337G REV L 062613
Marking Diagram (8 MSOP)
Marking Diagram (16 SOIC)
Marking Diagram (8 SOIC)
Marking Diagram (16 QFN)
Notes:
1. # = product stepping.
2. $ = mark code.
3. ** = sequential lot code.
4. YYWW is the last two digits of the year and week that the part was assembled.
5. “XXX” = traceability (lot code).
6. “G” denotes RoHS compliant package.
7. “I” denotes industrial grade.
8. Bottom marking: country of origin if not USA.
7GGI
YYWW$
18
916
IDT
1337AGC
SRGI
YYWW**$
IDT
1337G
DCGI
YYWW$
14
58
Industrial
IDT
1337G
DCGK
YYWW$
14
58
Extended
XXX
YWW$
37GI
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Package Outline and Package Dimensions (8-pin SOIC, 150 Mil. Body)
Package dimensions are kept current with JEDEC Publication No. 95
INDEX
AREA
1 2
8
D
E
SEATING
PLANE
A1
A
e
- C -
B
.10 (.004) C
C
L
H
h x 45
Millimeters Inches
Symbol Min Max Min Max
A 1.35 1.75 .0532 .0688
A1 0.10 0.25 .0040 .0098
B 0.330.51.013.020
C 0.19 0.25 .0075 .0098
D 4.80 5.00 .1890 .1968
E 3.80 4.00 .1497 .1574
e 1.27 BASIC 0.050 BASIC
H 5.80 6.20 .2284 .2440
h 0.250.50.010.020
L 0.401.27.016.050
0808
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Package Outline and Package Dimensions (8-pin MSOP, 3.00 mm Body)
Package dimensions are kept current with JEDEC Publication No. 95
INDEX
AREA
1 2
8
D
E1 E
SEATING
PLANE
A
1
A
A
2
e
- C -
b
aaa C
c
L
*For reference only. Controlling dimensions in mm.
Millimeters Inches*
Symbol Min Max Min Max
A--1.10--0.043
A1 0 0.15 0 0.006
A2 0.79 0.97 0.031 0.038
b 0.22 0.38 0.008 0.015
C 0.08 0.23 0.003 0.009
D 3.00 BASIC 0.118 BASIC
E 4.90 BASIC 0.193 BASIC
E1 3.00 BASIC 0.118 BASIC
e 0.65 Basic 0.0256 Basic
L 0.40 0.80 0.016 0.032
0808
aaa - 0.10 - 0.004
IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC
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IDT1337G REV L 062613
Package Outline and Package Dimensions (16-pin SOIC, 300 mil Body)
Package dimensions are kept current with JEDEC Publication No. 95
INDEX
AREA
1 2
16
D
E1 E
SEATING
PLANE
A
1
A
A
2
e
- C -
b
aaa C
c
L
*For reference only. Controlling dimensions in mm.
Millimeters Inches*
Symbol Min Max Min Max
A -- 2.65 -- 0.104
A1 0.10 -- 0.0040 --
A2 2.05 2.55 0.081 0.100
b 0.33 0.51 0.013 0.020
c 0.18 0.32 0.007 0.013
D 10.10 10.50 0.397 0.413
E 10.00 10.65 0.394 0.419
E1 7.40 7.60 0.291 0.299
e 1.27 Basic 0.050 Basic
L 0.40 1.27 0.016 0.050
0808
aaa - 0.10 - 0.004
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
IDT®
REAL-TIME CLOCK WITH I
2
C SERIAL INTERFACE 25
IDT1337G REV L 062613
Package Outline and Package Dimensions (16-pin QFN 3x3mm)
Package dimensions are kept current with JEDEC Publication No. 95
Millimeters
Symbol Min Max
A0.801.00
A1 0 0.05
A3 0.20 Reference
b0.180.30
e 0.50 BASIC
N16
ND4
NE4
D x E BASIC 3.00 x 3.00
D2 1.55 1.80
E2 1.55 1.80
L0.300.50
Sawn
Singulation
1
2
N
E
D
Index Area
Top View
Seating Plane
A3
A1
C
A
L
E2 E2 2
D2
D22
e
C0.08
(Ref)
ND & NE
Odd
(Ref)
ND & NE
Even
(ND-1)x
(Ref) e
N
1
2
b
Thermal Base
(Typ)
If ND & NE
are Even
(NE-1)x
(Ref) e
e2
IDT1337G
REA LTIME CLOCK WITH SERIAL INTERFACE RTC
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Ordering Information
The 1337GC packages are RoHS compliant. Packages without the integrated crystal are Pb-free; packages that include the
integrated crystal (as designated with a “C” before the two-letter package code) may include lead that is exempt under RoHS
requirements. The lead finish is JESD91 category e3.
“G” is the device revision designator and will not correlate to the datasheet revision.
While the information presented herein has been checked for both accuracy and reliability, Integrated Device Technology (IDT) assumes
no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would result from its use. No
other circuits, patents, or licenses are implied. This product is intended for use in normal commercial applications. Any other applications
such as those requiring extended temperature range, high reliability, or other extraordinary environmental requirements are not
recommended without additional processing by IDT. IDT reserves the right to change any circuitry or specifications without notice. IDT
does not authorize or warrant any IDT product for use in life support devices or critical medical instruments.
Part / Order Number Markings Shipping Packaging Package Temperature
1337GDVGI see page 20 Tubes 8-pin MSOP -40 to +85 C
1337GDVGI8 Tape and Reel 8-pin MSOP -40 to +85 C
1337AGCSRGI Tubes 16-pin SOIC -40 to +85 C
1337AGCSRGI8 Tape and Reel 16-pin SOIC -40 to +85 C
1337GDCGI Tubes 8-pin SOIC -40 to +85 C
1337GDCGI8 Tape and Reel 8-pin SOIC -40 to +85 C
1337GDCGK Tubes 8-pin SOIC -40 to +105 C
1337GDCGK8 Tape and Reel 8-pin SOIC -40 to +105 C
1337GNLGI Tubes 16-pin QFN -40 to +85 C
1337GNLGI8 Tape and Reel 16-pin QFN -40 to +85 C
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Revision History
Rev. Date Originator Description of Change
A 12/12/08 J.Sarma New device. Preliminary release.
B 01/28/09 A. Tsui Added 16-pin QFN package and ordering info.
C 02/04/09 A. Tsui Updated 16-pin QFN pinout.
D 04/03/09 A. Tsui Added 5µA Typ. to Active Supply Current spec.
E 05/26/09 A. Tsui Added top-side markings.
F 11/10/09 Added “Handling, PCB Layout, and Assembly” section.
G 11/16/09 A. Tsui Changed series resistance parameter from 50 to 80 kOhm.
H 08/02/10 A. Tsui Added extended temperature range for 8-pin SOIC.
J 03/01/11 A. Tsui Updated Standard Mode specs for “Rise/Fall Time of Both SDA and SCL Signals”.
K 09/20/12 J. Chao 1. Moved from Fab4 to TSMC. QA requested change in the marking of only the 16-pin
SOIC device with internal crystal to add “A” due to the fact that TSMC uses a different
crystal than Fab4. Notification of a change in orderables was initiated with PCN A1208-06.
2. . Updated 16-pin SOIC marking diagram and ordering information to include "A".
L 10/24/12 A. Tsui 1. Updated IDD specs per TSMC’s characterization data.
2. Updated top-side device markings.
L 06/26/13 J. Chao 1. Added verbiage for Bit0, Bit1, and Bit2 descriptors for further clarification.
2. Added "Alarm/Interrupt table for the aforementioned bits for further clarification.
3. No change to revision letter - only the revision date.
© 2013 Integrated Dev ice Tech nology, Inc. All righ ts reserved. Product spec ifications subject to c hange without notice. IDT an d the IDT logo are tra demarks of Integrated Devi ce
Tec hnology, Inc. Accelerated Thinking is a service mark of In tegrated Device Technology, Inc. All other brands, product names a nd marks a re or ma y be tr ademarks or regist ered
trademarks used to identify products or services of their respective owners.
Printed in USA
Corporate Headquarters
Integrated Device Technology, Inc.
www.idt.com
For Sales
800-345-7015
408-284-8200
Fax: 408-284-2775
For Tech Support
www.idt.com/go/clockhelp
Innovate with IDT and accelerate your future networks. Contact:
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IDT1337G
REAL-TIME CLOCK WITH I2C SERIAL INTERFACE RTC