DS3900K# Maxim Integrated Products, DS3900K# Datasheet - Page 9

• Manufacturer Part Number: DS3900K#
• Description: Power Management Modules & Development Tools 2-WIRE BUS INTERFACE NTERFACE EV KIT ROHS
• Manufacturer: Maxim Integrated Products

Specifications of DS3900K#

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

is tristated and the input is read. The pin remains in a
high-impedance state until a write operation is per-
formed. As mentioned before, all I/O pins, except P3,
are inputs on power-up.
Note: If an I/O pin is being used for both reads and
writes, take care to avoid bus contention.
Since software can only change a single pin at a time,
the DS3900 is much slower when communicating using
the bit I/O commands. For some applications, this is
acceptable since the 57600 baud communications
along with the streamline 2-byte command system allow
pins to be changed hundreds of times a second. If the
design requires higher performance than 100s of pin
changes per second the DS3900 may not be a good
choice for that general-purpose bit I/O application.
The DS3900 has decoupling on its PC board, but due to
the high periodic current draw of the RS232 transceiver.
It is recommended to place a decoupling capacitor
(47µF, Tantalum capacitor) next to the connector on the
board that the DS3900 will be mounted.
Moving the switches to the on (labeled “ON” on the
switch) position enables the integral pullups. This con-
nects 4.7kΩ pullup resistors to the SDA and SCL
buses, and it eliminates the need to place external
pullup resistors on the application board for 2-wire
Decoupling the DS3900’s V
Application Information
Using the Integral Pullups
_____________________________________________________________________
Serial Communications Module
CC
Supply
communication. In the event that the application board
already has pullups present, disconnect the integral
pullups by placing the switches in the off position. This
eliminates the extra (unnecessary) pullup strength,
because having both the integral pullup and the appli-
cation board’s pullup on at the same time could poten-
tially cause problems for either the DS3900 or the
2-wire slaves, which are required to pull the buses low.
Additionally, when P10 and P11 are used as bit I/O
pins, it can be advantageous to disconnect the pullups
to reduce the through current when either signal is dri-
ven low. For bit I/O operations, writing the signal to a ‘1’
enables a PMOS driver that drives the signal high.
However, it is also possible to use P10 and P11 as
open-collector I/O pins by enabling the pullups and
performing only read and write ‘0’ operations. As long
as a ‘1’ is never written to P10 or P11 it appears as an
open-collector output. This is how the firmware manufac-
tures the open-collector output for the 2-wire interface.
The DS3900 module and the bundled software are
intended only to be used to evaluate Maxim and Dallas
Semiconductor’s integrated circuits. The software is pro-
vided “as is”, without warranty of any kind, express or
implied, including but not limited to the warranties of
merchantability, fitness for a particular purpose and non-
infringement. In no event shall Dallas Semiconductor be
liable for any claim, damages or other liability, whether in
an action of contract, tort or otherwise, arising from, out
of, or in connection with the software or the use or other
dealings in the software.
For Evaluation Kits
Intended Use
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