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