Mode Selection
The state of the mode select pins M0, M1, and M2
determines which serial interface protocol is selected
(Table 1). The state of the DCE/DTE input determines
whether the transceiver will be configured as a DTE or
a DCE serial port. When the DCE/DTE input is logic
HIGH, driver T3 is activated and receiver R1 is dis-
abled. When the DCE/DTE input is logic LOW, driver T3
is disabled and receiver R1 is activated. M0, M1, M2,
and DCE/DTE are internally pulled up to V
CC
to ensure
a logic HIGH if left unconnected.
The MAX3170’s mode can be selected through soft-
ware control of the M0, M1, M2, and DCE/DTE inputs.
Alternatively, the mode can be selected by shorting the
appropriate combination of mode control inputs to
GND. The inputs left floating will be internally pulled up
to V
CC
(logic HIGH). If the M0, M1, and M2 mode
inputs are all unconnected, the MAX3170 will enter no-
cable mode and the supply current will drop to 1mA.
No-Cable Mode
The MAX3170 will enter no-cable mode when the mode
select pins are left unconnected or tied high (M0 = M1
= M2 = 1). In this mode, the multiprotocol drivers and
receivers are disabled and the supply current drops to
1mA. The receiver outputs enter a high-impedance
state in no-cable mode, which allows these output lines
to be shared with other receivers (the receiver outputs
have an internal pull-up resistor to pull the outputs
HIGH if not driven). Also, in no-cable mode, the trans-
mitter outputs enter a high-impedance state so that
these output lines can be shared with other devices.
Dual Charge-Pump Voltage Converter
The MAX3170’s internal power supply consists of a reg-
ulated dual charge pump that provides positive and
negative output voltages from a +3.3V supply. The
charge pump operates in discontinuous mode: if the
output voltage is less than the regulated voltage, the
charge pump is enabled; if the output voltage exceeds
the regulated voltage, the charge pump is disabled.
Each charge pump requires a flying capacitor (C1, C2)
and a reservoir capacitor (C3, C4) to generate the V+
and V- supplies. See Figure 6 for charge-pump con-
nections.
Fail-Safe Receivers
The MAX3170 guarantees a logic-high receiver output
when the receiver inputs are shorted or open, or when
they are connected to a terminated transmission line
with all drivers disabled. This is done by setting the
MAX3170
+3.3V, Multiprotocol, 3 Tx/3 Rx, Software-
Selectable Clock/Data Transceiver
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Table 1. Mode Selection
