UG-1677
Rev. 0 | Page 6 of 12
Link Jumper Connection
Description
LK5
A
Connects the INVR input of the
to the V
IO
pin. This setting enables the receiver inversion feature.
B
Connects the INVR input of the
to the INVR terminal on the P3 connector.
C
Connects the INVR input of the
to the GND
1
pins. This setting is used for normal receiver operation.
LK6
Inserted
Connects the Pin B of the
to Pin Z.
Not inserted
Disconnects the Pin B of the
from Pin Z.
LK7
Inserted
Connects the Pin A of the
to Pin Y.
Not inserted
Disconnects the Pin A of the
from Pin Y.
LK8
A
Connects the V
CC
pin of the
to the VREG_IN terminal on the P1 connector. This option bypasses the
regulator and allows an external power supply to connect directly to the V
CC
pin of the
B
Powers the V
CC
pin of the
with a regulated 3.3 V power supply from the
must be supplied with at least 4 V through the VREG_IN terminal on the P1 connector.
C
Powers the V
CC
pin of the
with a regulated 5 V power supply from the
must be supplied with at least 6 V through the VREG_IN terminal on the P1 connector.
LK9
Inserted
Connects the V
CC
pin of the
to the V
IO
pin.
Not inserted
Disconnects the V
CC
pin of the
from the V
IO
pin. The V
IO
pin is powered from the VIO terminal
on the P1 connector.
LK10 Inserted
Connects the 120 Ω RT2 termination resistor across the Pin A and Pin B of the
Not inserted
Disconnects the 120 Ω RT2 termination resistor across the Pin A and Pin B of the
LK11 Inserted
Connects the 120 Ω RT1 termination resistor across the Pin Y and Pin Z of the
Not inserted
Disconnects the 120 Ω RT1 termination resistor across the Pin Y and Pin Z of the
OTHER BOARD COMPONENTS
The EVAL-ADM2867EEBZ has footprints for the RT1 and RT2
termination resistors. Two 120 Ω termination resistors are fitted to
the EVAL-ADM2867EEBZ, but these resistors can be removed or
replaced with a resistor of a different value as needed. Insert the
LK11 jumper to add a 120 Ω load to the RS-485 driver. When LK6,
LK7, and LK10 are inserted, an additional 120 Ω termination
resistor is connected, resulting in a 60 Ω load on the RS-485 driver.
Biasing Resistors for Bus Idle Fail-Safe
The
has a built in receiver fail-safe for the bus idle
condition, but there are footprints on the EVAL-ADM2867EEBZ
for fitting the R10 and R11 pull-up resistors to the V
ISO
supply on
Pin A and Pin Y of the
, as well as the R12 and R13
pull-down resistors to the GND
2
supply pins on Pin B and Pin Z.
These resistors can be fitted if the user is connecting to other
devices that require external biasing resistors on the bus. The exact
value required for a 200 mV minimum differential voltage in bus
idle condition depends on the minimum supply voltage and the
termination scheme. For 5 V transceiver operation, 1140 Ω is
recommended. For 3.3 V transceiver operation, 900 Ω is
recommended.
See the
RS-485/RS-422 Circuit
Implementation Guide
for more information about the bus idle
fail-safe.
On-Board
Oscillator
An
clock oscillator is provided on the EVAL-
ADM2867EEBZ to allow efficient evaluation of the device
without the need for an external signal source.
To use the
oscillator for evaluation, insert the LK3 jumper
into Position BC. This setting connects the clock oscillator output
to the TxD input pin of the
The R2 and R3 resistors can be used to configure the switching
frequency of the clock oscillator within the 100 kHz to 12.5 MHz
range. Calculate the frequency using the following equation:
20 kΩ
=10 MHz
16 kΩ (R2 + R3) 2 MΩ
(R2 + R3)
OSC
f
≤
≤
where
f
OSC
is the output frequency of the
oscillator is powered from the V
IO
supply, and
must only be used when the V
IO
supply voltage is between 2.7 V
and 5.5 V.
LDO Regulator
The EVAL-ADM2867EEBZ features an on-board
LDO regulator that allows flexible power supply configurations
during evaluation.
To use the on-board regulator, insert the LK8 jumper into
Position B or Position C. This setting connects the regulator output
to the V
CC
pin of the
. In this configuration, power
must be supplied to the VREG_IN input on the P1 connector.
The
LDO regulator can be configured to provide
regulated 3.3 V or 5 V power to the V
CC
pin of the
via
the LK8 jumper. When using the
LK8 jumper at Position C to provide a regulated 5 V power supply
to the V
CC
pin of the
. Insert the LK8 jumper at
Position B to provide a 3.3 V power supply to the V
CC
pin of the
. Note that when LK8 is inserted at Position B, 5 V
transceiver operation is not supported.
