THVD1510 Datasheet, PDF (15/39 Pages) Texas Instruments – 5-V RS-485 Transceivers With 18-kV IEC ESD Protection

www.ti.com
THVD1510, THVD1512
THVD1550, THVD1551, THVD1552
SLLSEV1 – SEPTEMBER 2017
9.3 Feature Description
Internal ESD protection circuits of the THVD15xx protect the transceivers against electrostatic discharges (ESD)
according to IEC 61000-4-2 of up to ±18 kV and against electrical fast transients (EFT) according to IEC 61000-
4-4 of up to ±4 kV. With careful system design, one could achieve ±4 kV EFT Criterion A (no data loss when
transient noise is present).
The THVD15xx device family provides internal biasing of the receiver input thresholds in combination with large
input-threshold hysteresis. The receiver output remains logic high under a bus-idle or bus-short conditions
without the need for external failsafe biasing resistors. Device operation is specified over a wide ambient
temperature range from –40°C to 125°C.
9.4 Device Functional Modes
9.4.1 Device Functional Modes for THVD1510 and THVD1550
When the driver enable pin, DE, is logic high, the differential outputs A and B follow the logic states at data input
D. A logic high at D causes A to turn high and B to turn low. In this case the differential output voltage defined as
V_OD = V_A – V_B is positive. When D is low, the output states reverse: B turns high, A 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
A turns high and B turns low.
Table 1. Driver Function Table for THVD1510 and THVD1550
INPUT
D
H
L
X
X
OPEN
ENABLE
DE
H
H
L
OPEN
H
OUTPUTS
A
B
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
When the receiver enable pin, RE, is logic low, the receiver is enabled. 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 lower 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.
When RE is logic high or left open, the receiver output is high-impedance and the magnitude and polarity of V_ID
are irrelevant. 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 2. Receiver Function Table for THVD1510 and THVD1550
DIFFERENTIAL INPUT
V_ID = V_A – V_B
V_TH+ < V_ID
V_TH- < V_ID < V_TH+
V_ID < V_TH-
X
X
Open-circuit bus
Short-circuit bus
Idle (terminated) bus
ENABLE
RE
L
L
L
H
OPEN
L
L
L
OUTPUT
R
H
?
L
Z
Z
H
H
H
FUNCTION
Receive valid bus high
Indeterminate bus state
Receive valid bus low
Receiver disabled
Receiver disabled by default
Fail-safe high output
Fail-safe high output
Fail-safe high output
Copyright © 2017, Texas Instruments Incorporated
Submit Documentation Feedback
15
Product Folder Links: THVD1510 THVD1512 THVD1550 THVD1551 THVD1552