SNAA377 December   2025 LMK05318 , LMK05318B , LMK5B12204 , LMK5B12212 , LMK5B33216 , LMK5B33414 , LMK5C22212A , LMK5C23208A , LMK5C33216 , LMK5C33216A , LMK5C33414A

 

  1.   1
  2.   Trademarks
  3.   Abstract
  4. 1Introduction
  5. 2General Termination Guidelines
    1. 2.1 Identify the Driver and Receiver Requirements
    2. 2.2 Determine the Coupling Type
      1. 2.2.1 DC-Coupled Signal
      2. 2.2.2 AC-Coupled Signal
  6. 3Differential
    1. 3.1 Setting the Common-Mode Voltage (Thevenin Termination)
    2. 3.2 LVPECL
      1. 3.2.1 DC-Coupled LVPECL
      2. 3.2.2 AC-Coupled LVPECL
    3. 3.3 LVDS
      1. 3.3.1 DC-Coupled LVDS
      2. 3.3.2 AC-Coupled LVDS
    4. 3.4 HSDS
      1. 3.4.1 DC-Coupled HSDS
      2. 3.4.2 AC-Coupled HSDS
    5. 3.5 HCSL
      1. 3.5.1 DC-Coupled HCSL
      2. 3.5.2 AC-Coupled HCSL
    6. 3.6 LP-HCSL
      1. 3.6.1 DC-Coupled LP-HCSL
      2. 3.6.2 AC-Coupled LP-HCSL
  7. 4Single-Ended
    1. 4.1 LVCMOS
      1. 4.1.1 DC-Coupled LVCMOS (Series Termination)
      2. 4.1.2 AC-Coupled LVCMOS (Series Termination)
    2. 4.2 Differential P or N
      1. 4.2.1 DC-Coupled Differential P or N
  8. 5Summary
  9. 6References

4.1.1 DC-Coupled LVCMOS (Series Termination)

LVCMOS drivers are typically source-terminated and internally biased to mid-level of VOH (or VOH/2), where VOH tends to be near VDD and VOL near 0V.

General Guidelines

  • Avoid placing resistors to ground on the CMOS outputs to prevent high current consumption. If pull-downs are used to reduce the voltage swing, confirm the current limit of the output driver is not violated. Check the driver data sheet.
  • A series resistor (RS) can be placed in the case the output impedance (RO) does not match the required transmission line impedance (ZO).
  • Place RS as close to the output pins as possible to match the impedance, correct the overshoot, and reduce the output slew rate. Fulfill the equation to maintain impedance-matched outputs:
    • ZO = RO + RS
  • When RO is unknown, set RS = 0Ω in the initial design. RS can be adjusted for impedance matching after testing the signal integrity of the PCB.

Example Termination:

DC-Coupled LVCMOS to LVCMOS

DC-Coupled LVCMOS to LVCMOS Figure 4-1 DC-Coupled LVCMOS to LVCMOS