THVD1510 Datasheet, PDF (16/39 Pages) Texas Instruments – 5-V RS-485 Transceivers With 18-kV IEC ESD Protection

THVD1510, THVD1512
THVD1550, THVD1551, THVD1552
SLLSEV1 – SEPTEMBER 2017
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9.4.2 Device Functional Modes for THVD1551
For this device, the driver and receiver are fully enabled, thus the differential outputs Y and Z follow the logic
states at data input D at all times. A logic high at D causes Y to turn high and Z to turn low. In this case, the
differential output voltage defined as V_OD = V_Y – V_Z is positive. When D is low, the output states reverse: Z turns
high, Y becomes low, and VOD is negative. The D pin has an internal pull-up resistor to V_CC, thus, when left
open while the driver is enabled, output Y turns high and Z turns low.
INPUT
D
H
L
OPEN
Table 3. Driver Function Table for THVD1551
OUTPUTS
Y
Z
H
L
L
H
H
L
FUNCTIONS
Actively drive bus high
Actively drive bus low
Actively drive bus high by default
When the differential input voltage defined as V_ID = V_A – V_B is higher than the positive input threshold, V_TH+, the
receiver output, R, turns high. When V_ID is less than the negative input threshold, V_TH–, the receiver output, R,
turns low. If V_ID is between V_TH+ and V_TH– the output is indeterminate. Internal biasing of the receiver inputs
causes the output to go failsafe-high when the transceiver is disconnected from the bus (open-circuit), the bus
lines are shorted to one another (short-circuit), or the bus is not actively driven (idle bus).
Table 4. Receiver Function Table for THVD1551
DIFFERENTIAL INPUT
V_ID = V_A – V_B
V_TH+ < V_ID
V_TH- < V_ID < V_TH+
V_ID < V_TH-
Open-circuit bus
Short-circuit bus
Idle (terminated) bus
OUTPUT
R
H
?
L
H
H
H
FUNCTION
Receive valid bus high
Indeterminate bus state
Receive valid bus low
Fail-safe high output
Fail-safe high output
Fail-safe high output
9.4.3 Device Functional Modes for THVD1512 and THVD1552
When the driver enable pin, DE, is logic high, the differential outputs Y and Z follow the logic states at data input
D. A logic high at D causes Y to turn high and Z to turn low. In this case the differential output voltage defined as
V_OD = V_Y – V_Z is positive. When D is low, the output states reverse: Z turns high, Y becomes low, and V_OD is
negative.
When DE is low, both outputs turn high-impedance. In this condition the logic state at D is irrelevant. The DE pin
has an internal pull-down resistor to ground, thus when left open the driver is disabled (high-impedance) by
default. The D pin has an internal pull-up resistor to V_CC, thus, when left open while the driver is enabled, output
Y turns high and Z turns low.
Table 5. Driver Function Table for THVD1512 and THVD1552
INPUT
D
H
L
X
X
OPEN
ENABLE
DE
H
H
L
OPEN
H
OUTPUTS
Y
Z
H
L
L
H
Z
Z
Z
Z
H
L
FUNCTION
Actively drive bus high
Actively drive bus low
Driver disabled
Driver disabled by default
Actively drive bus high by default
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