Novatel OEM719, Инструкция по установке и эксплуатации

Страница: 214 / 235

OEM7 Installation and Operation User Manual v4 214
E.1 EVENT_IN, EVENT_OUT and PPS Signal Protection
The following schematic shows appropriate signal conditioning for EVENT_IN (MKI), EVENT_OUT
(VARF) and PPS (TIMEMARK) signals.
Figure 58: Protection and Buffering for EVENT_IN, PPS and EVENT_OUT signals
The buffers (U1, U2) are chosen to provide additional drive strength for long cables. The series
terminations (R1, R2, R3, R4) are present to allow for signal integrity adjustments (to reduce
overshoot/undershoot, etc.). The passive component values may require tuning, depending on
the application.
The TVS (U3) provides protection from ESD/EFT events and some induced power line surges.
There are two implementations shown for the EVENT_IN signals. EVENT_IN1 is shown with basic
ESD/EFT protection, while EVENT_IN2 is shown with additional surge protection for harsh envir-
onments (see D1, R7, D2, D3 and R9). If the additional surge protection is to be used on a
design, the buffer must be included as well. This design has been used to protect EVENT_IN sig-
nals from EN61000-4-5 induced surges up to 2kV on several NovAtel enclosure products. If nano-
second-level timing is critical to the application, this protection circuit may be unsuitable, as it
causes a timing shift of a few microseconds to the EVENT signal (heavily dependent on tem-
perature).