MAX14890E Datasheet, PDF (18/30 Pages) Maxim Integrated Products – Overvoltage and Undervoltage Fault Detection

MAX14890E
Incremental Encoder Interface for RS-422,
HTL, and TTL with Digital Inputs
Detailed Description
The MAX14890E is an incremental encoder receiver
containing four differential receivers and two single-ended
receivers. All four differential receivers support RS-422
and TTL operation. Three of these differential receivers
can be configured for differential and single-ended HTL
operation. In RS-422 mode, these receivers feature a
wide common mode input range of -20V to +20V making
it resilient to common mode noise.
The auxiliary IEC 61131-2 Type-1/Type-3 24V digital
inputs allow connection of proximity sensors. The digital
inputs can be individually configured for TTL operation.
All receiver input signals are fault protected to voltage
shorts in the ±40V range. Per channel fault detection pro-
vides warning of irregular conditions, like small differential
signals, shorts, opens, over- and undervoltages.
SPI or Pin-Control Mode Selection
The MAX14890E provides a selectable SPI or pin inter-
face to set the input thresholds and functionality of the
receivers. Drive SPI high to use the SPI interface. Drive
SPI low to use the pin interface.
SPI mode allows for higher flexibility by allowing individual
receiver configuration. See the Serial SPI Control section
for more information.
TTL Operation
All 6 of the receivers can be configured for single-ended TTL
operation. Complimentary/unused inputs can be left uncon-
nected in all single-ended modes like TTL, DI, and SE-HTL.
In pin-control mode, drive the TTL/SDI and SNGL/CLK
inputs high to enable TTL operation on the RxA, RxB, and
RxZ receivers. To enable TTL operation on RxY receiver, set
DI/TTLY low. To enable TTL operation on the RxD2 or RxD3
receivers, drive the DI/TTL2 or DI/TTL3 inputs low. See the
Truth Tables section for more information.
In SPI mode, each receiver can be enabled for TTL opera-
tion individually. Set the associated _SNGL and _TTL bits
to enable TTL mode for each receiver. See the Serial SPI
Control section for more information.
Single-Ended HTL Operation (SE-HTL)
The RxA, RxB, and RxZ receivers can be configured for
single-ended HTL operation. Complimentary/unused inputs
can be left unconnected in all single-ended modes (TTL, DI,
and SE-HTL).
In pin-control mode, drive the TTL/SDI input low and the
SNGL/CLK input high to enable SE-HTL mode on the
RxA, RxB, and RxZ receivers.
In SPI mode, each of the RxA, RxB, and RxZ receivers
can be individually enabled for SE-HTL functionality. See
the Serial SPI Control section for more information.
Differential HTL (D-HTL) Operation
The RxA, RxB, and RxZ receivers can be configured
for D-HTL operation. Input signals up to ±40V can be
accepted in D-HTL mode.
In pin-control mode, set the SNGL/CLK and TTL/SDI
inputs low to enable D-HTL functionality for the RxA, RxB,
and RxZ receivers. See the Truth Tables section for more
information.
In SPI mode, each of the RxA, RxB, and RxZ receivers
can be individually enabled for D-HTL functionality. See
the Serial SPI Control section for more information.
RS-422 Operation
The RxA, RxB, RxZ, and RxY receivers can be configured
for RS-422 operation. These receivers include a wide
common-mode input range (-20V to +20V) in this mode.
In pin-control mode, set the SNGL/CLK input low and the
TTL/SDI input high to enable RS-422 functionality for the
RxA, RxB, RxZ, and RxY receivers. See the Truth Tables
section for more information.
In SPI mode, each receiver can be individually enabled
for RS-422 functionality. See the Serial SPI Control sec-
tion for more information.
Equivalent Input Circuit
In RS-422, TTL, SE-HTL, and D-HTL modes, the inputs
pins have the equivalent circuit shown in Figure 5. When
the RxA, RxB, RxZ, and/or RxY inputs are configured for
TTL mode and are open/not connected, the input is pulled
up to 2.64V (typ), resulting in a logic high on the receiver
output.
RxD2 and RxD3 have high impedance inputs in TTL
mode (Figure 6). Leaving DI2 or DI3 unconnected in this
mode will result in an unknown logic state on the receiver
output .
Detecting Faults
Signal integrity from the encoder is essential for reliable
system operation. Degraded signals could cause prob-
lems ranging from simple miscounts to loss of position.
The MAX14890E detects common RS-422/HTL/TTL/DI
faults. These faults include low differential input signals,
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