MAX13487E_08 Datasheet, PDF (4/8 Pages) Maxim Integrated Products – Evaluation Kit

MAX13487E Evaluation Kit
RS-485 Bus Pullup/Pulldown and
Termination Resistors Configuration
Jumpers JU6 and JU4 are provided for connecting the
mandatory pullup and pulldown resistors onto the RS-485
bus A and B lines, respectively. Pullup resistor R8 and
pulldown resistor R6 define the voltage on the A and B
lines in conjunction with R7 when the driver input (DI) is
high. See Table 3 for configuring the pullup and pulldown
resistors. R6 and R8 can be higher valued if the
differential terminal resistor (R7) is not used.
Jumper JU5 is provided for terminating the A and B bus
lines when the MAX13487E EV kit is connected at the
end of an RS-485 bus. Resistor R7 provides 120Ω of ter-
mination when jumper JU5 is used. See Table 4 for con-
figuring the termination mode.
Table 3. JU6, JU4 Functions, Pullup, Pulldown Resistors
SHUNT POSITION
None
A AND B LINE SIGNAL
Not pulled up or down
Installed
A signal pulled up, connected to VOUT
B signal pulled down to GND
Table 4. JU5 Functions, Bus Termination
SHUNT POSITION
None
Installed
A-B PINS AND RS-485 BUS TERMINATION
Not terminated
Terminated
EV KIT BUS CONNECTION
Mid point
End of bus line
Evaluating the MAX13488E IC and
Other Transformer Configurations/Designs
MAX13488E Evaluation
The MAX13487E EV kit can also evaluate the
MAX13488E IC. To evaluate the MAX13488E, replace
IC U1 with the MAX13488E. Note that the MAX13488E
driver slew rate is not limited and allows transmission
speeds of up to 16Mbps. Refer to the MAX13487E/
MAX13488E IC data sheet for additional information.
Smaller Transformer and 2000V_RMS
Isolation Design
The EV kit’s two-layer PCB is designed for 2500V_RMS
isolation, with 300 mils spacing between the PGND and
GND planes. Additionally, transformer T1 is rated for
3000V_RMS and is an integral part of the dielectric with-
stand voltage of the EV kit circuit. Photocouplers U4
and U5 are guaranteed to withstand 3750V_RMS.
However, the circuit uses the isolated transformer to
transfer power from the primary side to the secondary
side and the withstand voltage of the transformer, as
well as photocouplers U4 and U5, so the PCB must be
considered when designing and testing the EV kit cir-
cuit. For example, if less than 2500V_RMS isolation is
needed, a smaller 2000V_RMS transformer may be used
to save board area, but then the entire circuit will have
only 2000V_RMS of isolation.
4 _______________________________________________________________________________________