SLOS913A October   2015  – February 2017 SN55HVD75-EP

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics: 20 Mbps Device, Bit Time ≥50 ns
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Data Rate and Bus Length
        2. 9.2.1.2 Stub Length
        3. 9.2.1.3 Bus Loading
        4. 9.2.1.4 Receiver Failsafe
        5. 9.2.1.5 Transient Protection
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 External Transient Protection
        2. 9.2.2.2 Isolated Bus Node Design
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

8 Detailed Description

8.1 Overview

The SN55HVD75-EP is a low-power, half-duplex RS-485 transceiver available in a speed grade suitable for data transmission up to 20 Mbps.

This device has active-high driver enables and active-low receiver enables. A standby current of less than 2 µA can be achieved by disabling both driver and receiver.

8.2 Functional Block Diagram

SN55HVD75-EP fbdnew_sllse11.gif

8.3 Feature Description

Internal ESD protection circuits protect the transceiver against electrostatic discharges (ESD) according to IEC 61000-4-2 of up to ±12 kV, and against electrical fast transients (EFT) according to IEC 61000-4-4 of up to
±4 kV.

The SN55HVD75-EP half-duplex family provides internal biasing of the receiver input thresholds in combination with large input threshold hysteresis. At a positive input threshold of VIT+ = –20 mV and an input hysteresis of
VHYS = 50 mV, the receiver output remains logic high under a bus-idle or bus-short condition even in the presence of 140-mVPP differential noise without the need for external failsafe biasing resistors.

Device operation is specified over a wide ambient temperature range from –55°C to 125°C.

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 Function Table

INPUT ENABLE OUTPUTS DESCRIPTION
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 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 Function Table

DIFFERENTIAL INPUT ENABLE OUTPUT DESCRIPTION
VID = VA – VB RE R
VIT+ < VID 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 Failsafe high output.
Short-circuit bus L H Failsafe high output.
Idle (terminated) bus L H Failsafe high output.
SN55HVD75-EP hvd7x_hd_eq_i-o_sche_sllse11.gif Figure 14. Equivalent Input and Output Circuit Diagrams