Datasheet

Dual Serial UART with 128-Word FIFOs
MAX3109
63Maxim Integrated
Low-Power Operation
To reduce the power consumption during normal opera-
tion, the following techniques can be adopted:
• Do not use the internal PLL. This saves the most
power of the options listed here. Disable and bypass
the PLL. With the PLL enabled, the current to the
V
CC
supply is in the range of a few mA (depending
on clock frequency and multiplication factor), while it
drops to below 1mA if disabled.
• Use an external clock source. The lowest power
clocking mode is when an external clock signal is
used. This drops the power consumption to about half
that of an external crystal.
• Keeptheinternalclockratesaslowaspossible.
• UsealowvoltageontheV
CC
supply.
• Use an external 1.8V supply. This saves the power
dissipated by the internal 1.8V linear regulator for the
1.8V core supply. Connect an external 1.8V supply to
V
18
and disable the internal regulator by connecting
LDOEN to DGND.
Interrupts and Polling
Monitor the MAX3109 by polling the ISR register or by
monitoring the IRQ output. In polled mode, the IRQ
physical interrupt output is not used and the host control-
ler polls the ISR register at frequent intervals to establish
the state of the MAX3109.
Alternatively, the physical IRQ interrupt can be used to
interrupt the host controller after specified events, mak-
ing polling unnecessary. The IRQ output is an open-drain
output that requires a pullup resistor to V
L
.
Logic-Level Translation
The MAX3109 can be directly connected to transceivers
and controllers that have different supply voltages. The V
L
input defines the logic voltage levels of the controller inter-
face, while the V
EXT
voltage defines the logic of the trans-
ceiver interface. This ensures flexibility when selecting a
controller and transceiver. Figure 28 shows an example
of a configuration where the controller, transceiver, and
the MAX3109 are powered by three different supplies.
Figure 28. Logic-Level Translation
MAX3109
TX_
RX_
RTS_
AGND
DGND
V
L
V
CC
V
EXT
RST
IRQ
SPI/I
2
C
MAX14840E
TRANSCEIVER
V
CC
DI
DE
RO
V
DD
2.5V
1.8V 3.3V
MICROCONTROLLER