MAX3387 Maxim, MAX3387 Datasheet - Page 13

• Manufacturer Part Number: MAX3387
• Description: 3V / 15kV ESD-Protected / AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones
• Manufacturer: Maxim

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.
Figure 10. Loopback Test Results at 250kbps
R1OUT
T1OUT
3V, ±15kV ESD-Protected, AutoShutdown Plus
T1IN
RS-232 Transceiver for PDAs and Cell Phones
Typical PDA/Cell-Phone Application
V
CC
= 3.3V
______________________________________________________________________________________
2 s/div
5V/div
5V/div
5V/div
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 only 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.
As cell phone design becomes more like that of PDAs,
cell phones will require similar docking ability and com-
munication protocol. Cell phones operate on a single
lithium-ion (Li+) battery and work with a power-supply
voltage of +2.7V to +4V. The baseband logic coming
from the phone connector can be as low as 1.8V at the
transceivers. To prevent forward biasing of a device
internal to the cell phone, the MAX3387E comes with a
logic power-supply pin (V
presented to the phone. The receiver outputs will sink
to zero for low outputs, but will not exceed V
highs. The input logic levels for the transmitters are also
altered, scaled by the magnitude of the V
device will work with V
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 1.8V.
TRANSISTOR COUNT: 1267
L
L
as low as 1.8V before the
) that limits the logic levels
Chip Information
L
input. The
L
for logic
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