SLLS934F November 2008 – November 2015 SN65HVD11-HT
PRODUCTION DATA.
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Parameter Measurement Information
- 8 Detailed Description
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
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8 Detailed Description
8.1 Overview
The SN65HVD11-HT device is a 3.3 V, half-duplex, RS-485 transceiver available in 3 speed grades suitable for data transmission up to 32 Mbps, 10 Mbps, and 1 Mbps, respectively.
The device has active-high driver enables and active-low receiver enables. A standby current of less than
5 µA can be achieved by disabling both driver and receiver.
8.2 Functional Block Diagram
8.3 Feature Description
Internal ESD protection circuits protect the transceiver bus terminals against ±16-kV Human Body Model (HBM) electrostatic discharges and ±4-kV electrical fast transients (EFT) according to IEC61000-4-4.
The SN65HVD11-HT half-duplex device provides internal biasing of the receiver input thresholds for open-circuit, bus-idle, or short circuit failsafe conditions, and a typical receiver hysteresis of 35 mV.
8.4 Device Functional Modes
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 VOD = VA – VB is positive. When D is low, the output states reverse, B turns high, A becomes low, and VOD 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 pulldown resistor to ground; thus, when left open, the driver is disabled (high-impedance) by default. The D pin has an internal pullup resistor to VCC; thus, when left open while the driver is enabled, output A turns high and B turns low.
Table 1. Driver Functions(1)
| INPUT | ENABLE | OUTPUTS | FUNCTION | |
|---|---|---|---|---|
| D | DE | A | B | |
| H | H | H | L | Actively drive bus High |
| L | H | L | H | Actively drive bus Low |
| X | L | Z | Z | Driver disabled |
| X | OPEN | Z | Z | Driver disabled by default |
| OPEN | H | H | L | 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 VID = VA – VB is positive and higher than the positive input threshold, VIT+, the receiver output, R, turns high. When VID is negative and lower than the negative input threshold, VIT–, the receiver output, R, turns low. If VID is between VIT+ and VIT–, the output is indeterminate.
When RE is logic high or left open, the receiver output is high-impedance and the magnitude and polarity of VID 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 (short-circuit), or the bus is not actively driven (idle bus).
Table 2. Receiver Functions(1)
| DIFFERENTIAL INPUT VID = VA – VB |
ENABLE RE |
OUTPUT R |
FUNCTION |
|---|---|---|---|
| VID > VIT+ | L | H | Receive valid bus High |
| VIT– < VID < VIT+ | L | ? | Indeterminate bus state |
| VID < VIT– | L | L | Receive valid bus Low |
| X | H | Z | Receiver disabled |
| X | OPEN | Z | Receiver disabled by default |
| Open-circuit bus | L | H | Fail-safe high output |
| Short circuit bus | L | H | Fail-safe high output |
8.4.1 Low-Power Standby Mode
When both the driver and receiver are disabled (DE low and RE high) the device is in standby mode. If the enable inputs are in this state for less than 60 ns, the device does not enter standby mode. This guards against inadvertently entering standby mode during driver or receiver enabling. Only when the enable inputs are held in this state for 300 ns or more, the device is assured to be in standby mode. In this low-power standby mode, most internal circuitry is powered down, and the supply current is typically less than 1 µA. When either the driver or the receiver is reenabled, the internal circuitry becomes active.