3V, ±±15V EꢀDꢁ-rotected, Autoꢀhutdown -lus
Rꢀꢁ232 Transceiver for -DAs and Cell -hones
MAX387E
As cell phone design becomes more li5e that of PDAs,
cell phones will require similar doc5ing abilitꢂ and com-
munication protocol. Cell phones operate on a single
5V/div
5V/div
5V/div
T1IN
T1OUT
R1OUT
lithium-ion (Li+) batterꢂ and wor5 with a power-supplꢂ
voltage of +2.7V to +4V. The baseband logic coming
from the phone connector can be as low as ±.8V at the
transceivers. To prevent forward biasing of a device
internal to the cell phone, the MAX3387E comes with a
logic power-supplꢂ pin (V ) that limits the logic levels
L
presented to the phone. The receiver outputs will sin5
to zero for low outputs, but will not exceed V for logic
L
highs. The input logic levels for the transmitters are also
V
CC
= 3.3V
altered, scaled bꢂ the magnitude of the V input. The
L
device will wor5 with V as low as ±.8V before the
L
2μs/div
charge-pump noise will begin to cause the transmitter
outputs to oscillate. This is useful with cell phones and
other power-efficient devices with core logic voltage
levels that go as low as ±.8V.
Figure ±0. Loopbac5 Test Results at 2105bps
Chip Information
Typical -DA/Cellꢁ-hone Application
The MAX3387E is designed with PDA applications in
mind. Two transmitters and two receivers handle stan-
dard full-duplex communication protocol, while an extra
transmitter allows a ring indicator signal to alert the
UART on the PC. Without the ring indicator transmitter,
solutions for these applications would require software-
intensive polling of the cradle inputs.
PROCESS: ꢁiCMOS
-ac5age Information
For the latest pac5age outline information and land patterns,
go to www.maxim-iꢂ.ꢂom/paꢂ5ages. Note that a “+”, “#”, or
“-” in the pac5age code indicates RoꢀS status onlꢂ. Pac5age
drawings maꢂ show a different suffix character, but the drawing
pertains to the pac5age regardless of RoꢀS status.
The ring indicate (RI) signal is generated when a PDA,
phone, or other “cradled” device is plugged into its cradle.
This generates a logic-low signal to the RI transmitter
input, creating +6V at the ring indicate pin. The PC’s
UART RI input is the onlꢂ pin that can generate an inter-
rupt from signals arriving through the RS-232 port. The
interrupt routine for this UART will then service the RS-
232 full-duplex communication between the PDA and
the PC.
PACKAGꢀ ꢆYPꢀ PACKAGꢀ Cꢇꢁꢀ ꢁꢇCUMꢀNꢆ Nꢇ.
24 TSSOP
U24+±
2±-0066
______________________________________________________________________________________ ±3
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
