NXP Semiconductors OM13260, Руководство по установке, Страница: 21 / 71

NXP Semiconductors
UMxxxxx
Install Guide
All information provided in this document is subject to legal disclaimers.
Preliminary 1
— September 6, 2013
© NXP B.V. 2013. All rights reserved.
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Product portfolio.
Note: The PCA9901 will be made obsolete, and will not be present on future versions of the Fm+
Development Board (OM13260).
The operation of the Fm+ Development Board (OM13260) is greatly enhanced by third-party tools (not
supplied in the kit) that may be attached to either I2C Bus through dedicated connectors (Bus 1, CN17
and Bus2, CN18), labeled ‘TESTER’.
5.2 Circuit Description
The schematic diagram has multiple sheets. For clarification only fragments of the schematic are
shown here. The full schematic should be downloaded if required. The following pages are divided in to
several sections covering the Power Supply, USB Interface, Bus1, Bus2, and support circuits.
5.2.1 Power Supply
The Fm+ Development Board (OM13260) operates from DC, either from the USB Host connector (CN5)
or an optional external AC-DC Power Adapter (not supplied in the kit) via connector (CN6). See figure
5.2 and figure 5.3. Selection of the power source is automatic, using ORing diodes (D1 and D2). The
main power on the Fm+ Development Board (OM13260) is 3.3V, from a linear regulator (IC1) but some
of the circuits are powered directly from the incoming supply, which is a nominal 5V. Linear regulator
(IC1) uses the PCB bottom layer copper as a heat sink. The Fm+ Development Board (OM13260)
external DC input is protected against reverse polarity or overvoltage by Zener diode (D3). Both input
sources are scaled by resistor dividers (R1, R2 and R39, R40) and fed to the MCU (IC5) Port1 ADC inputs
for voltage level monitoring. The VBUS from the USB Host is fed to the MCU Port0 so that the MCU can
detect that a USB connection is available. Green LED (D4) confirms 5V and Green LED (D5) confirms
3.3V.