LTC2872
TesT circuiTs
R
L
Y
V
L
OR
GND
DY
C
L
DRIVER
Z
DXEN
R
L
C
L
V
CC
OR
GND
Y OR Z
GND
OR
V
CC
DXEN
�½V
L
t
ZLD485
,
t
ZLSD485
�½V
CC
�½V
L
t
LZD485
0.5V
0.5V
t
HZD485
V
L
0V
V
CC
V
OL
V
OH
0V
Z OR Y
t
ZHD485
,
t
ZHSD485
�½V
CC
2872 F05
Figure 5. RS485 Driver Enable and Disable Timing Measurements
V
AB
±V
AB
/2
V
CM
±V
AB
/2
A
B
RECEIVER
RA
C
L
RA
90%
10%
A–B
0V
t
PLHR485
�½V
L
t
RR485
t
SKEWR485
= t
PLHR485
– t
PHLR485
�½V
L
90%
10%
t
FR485
t
PHLR485
–V
AB
V
CC
0V
2872 F06
Figure 6. RS485 Receiver Propagation Delay Measurements (Note 5)
RXEN
A
B
RECEIVER
RA
R
L
C
L
RXEN
RA
�½V
L
t
ZLR485
�½V
L
t
LZR485
V
L
0V
V
L
0.5V
0.5V
t
HZR485
V
OL
V
OH
0V
0V TO 3V
3V TO 0V
V
L
OR
GND
RA
�½V
L
�½V
L
t
ZHR485
2872 F07
Figure 7. RS485 Receiver Enable and Disable Timing Measurements (Note 5)
2872f
12