LTC2874_15 Datasheet, PDF (17/44 Pages) Linear Technology – Quad IO-Link Master Hot Swap Controller and PHY

LTC2874
Operation
The LTC2874 is an industrial master Hot Swap bus
controller and physical interface (PHY) that provides
power and communication to four independent 3-wire
ports through cables up to 20m in length (see Figure 11A).
The primary applications are 24V systems specified by
IEC 61131-9 single-drop communication interface (SDCI)
for small sensors and actuators, commonly known as
IO-Link. Each port on the LTC2874 includes a Hot Swap
power supply output, data transceiver, and a current
sink, as shown in Figure 11B. This set of features allows
a typical master controller for four ports to be built with
the LTC2874, a host microcontroller, and four power
MOSFETs. The basic configuration is shown on page 1.
V_DD
Hot Swap
L+
L+
MASTER ^C/Q DEVICE
DRV
C/Q
L–
I_LL
L+, L–: POWER SUPPLY
C/Q: COMMUNICATION OR
SWITCHING SIGNAL
(A)
L–
(B)
2874 F11
Figure 11. (A) SDCI Class A 3-Wire Interface
(B) LTC2874 Master 3-Wire Interface Port
The bidirectional CQ pins are individually programmable
to operate in coded switching (COM) or switching signal
(standard IO, or SIO) format with reconfigurable behavior
including slew rate, noise suppression filter, and sinking
current. Drivers are protected against overcurrent faults
by circuit breakers that respond to a fault condition after
a mode-specific delay. For IO-Link compatibility, under
SPI control, the LTC2874 automatically generates 80µs
wake-up request (WURQ) pulses with correct polarity.
The LTC2874 turns each port’s supply voltage on and off
in a controlled manner using external N-channel MOSFETs.
External sense resistors individually set the current
limits for each port. Optional foldback behavior reduces
maximum power dissipation in the external MOSFETs
over their operating range. Each output is protected by a
circuit breaker that responds to an overcurrent fault after
a programmable timeout delay. A current-pulse-upon-18V
feature provides additional IO-Link capability for driving
heavy, nonlinear loads.
The rugged LTC2874 line interface has been designed to tol-
erate abusive conditions encountered on cable interfaces.
The CQ pins will tolerate 50V above L– (GND) and –50V
from V_DD. The L+ pins offer commensurate ruggedness for
power supply outputs (see Absolute Maximum Ratings).
Discrete power MOSFETs offer the best possible system
ruggedness and allow design flexibility. They also ensure
that ports remain fully independent in the event of extreme
fault conditions.
Normally, the LTC2874 will automatically restart after
supply overvoltage or port overcurrent timeout faults. The
auto-retry delay is programmable. Alternatively, latchoff
behavior is available. Overcurrent circuit breaker delays
for CQ pins are mode dependent; for L+ pins they are
programmable.
The LTC2874 provides a 4-wire SPI-compatible interface
for configuration and monitoring. The host can detect
faults and other events by polling four event registers or by
monitoring the IRQ pin, a programmable interrupt request.
Standalone Operation
The LTC2874 is designed for use with a host controller. The
SPI-compatible interface is the only means of operating
the Hot Swap power supply outputs. The transceivers can
operate standalone without the serial interface, restricted
by the default register configuration settings.
For more information www.linear.com/LTC2874
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