Datasheet

Manipulating the Address Counter for Reads: A
dummy write cycle can be used to force the address
counter to a particular value. To do this the master
generates a START condition, writes the slave address
byte (R/W
 = 0), writes the memory address where it
desires to read, generates a repeated START condi-
tion, writes the slave address byte (R/W = 1), reads
data with ACK or NACK as applicable, and generates a
STOPcondition.SeeFigure5forareadexampleusing
the repeated START condition to specify the starting
memory location.
Reading Multiple Bytes From a Slave: The read
operation can be used to read multiple bytes with a
singletransfer.Whenreadingbytesfromtheslave,the
master simply ACKs the data byte if it desires to read
another byte before terminating the transaction. After
the master reads the last byte it must NACK to indicate
theendofthetransferandthenitgeneratesaSTOP
condition.
Applications Information
Power-Supply Decoupling
To achieve the best results when using the device,
decouple the V
CC
 power supply with a 0.01µF and/or
0.1µF capacitor. Use a high-quality, ceramic, surface-
mount capacitor if possible. Surface-mount components
minimizeleadinductance,whichimprovesperformance,
and ceramic capacitors tend to have adequate high-
frequency response for decoupling applications.
Using an Open-Drain Output
TheSQW/INT output is open-drain and therefore requires
anexternal pullupresistorto realizea logic-highoutput
level.
SDA and SCL Pullup Resistors
SDAisanopen-drainoutputandrequiresanexternalpul-
lupresistortorealizealogic-highoutputlevel.
Because the device does not use clock cycle stretching,
a master using either an open-drain output with a pullup
resistororCMOSoutputdriver(push-pull)couldbeused
forSCL.
Battery Charge Protection
The device contains Maxim’s redundant battery-charge
protectioncircuittoprevent anychargingofanexternal
battery.TheDS1339BisrecognizedbytheUnderwriters
Laboratories(UL)underfileE141114.
Handling, PCB Layout, and Assembly
Avoid running signal traces under the package, unless a
ground plane is placed between the package and the sig-
nalline.Donotuseexternalcomponentstocompensate
for improper crystal selection.
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 mois-
ture-sensitive device (MSD) classifications.
Figure 6. Typical PCB Layout for Crystal
CRYSTAL
X1
X2
LOCAL GROUND PLANE (LAYER 2)
DS1339B Low-Current, I
2
C, Serial Real-Time Clock
For High-ESR Crystals
www.maximintegrated.com
MaximIntegrated │ 17