User manual

LPC4357 Developer’s Kit - User’s Guide
Page 55
Copyright 2012 © Embedded Artists AB
Figure 34 – Speaker Amplifier, U28
5.6.2 Current Consumption and Limits of USB Ports
The current consumption of LPC4357 OEM Board, OEM Base Board, and the 4.3 inch LCD Board is in
the region of 450-525mA. This is very close to what a normal USB-A port can supply. If the boards are
powered from a USB-A port (for example a PC or laptop) and there are problems, like spontaneous
resets or other strange things, it is likely that an external power supply is needed.
When using the 7 inch LCD Board and external power supply is always needed.
5.6.3 LCD flickering
When using the LCD expansion interface, R163 must be removed on the OEM Base Board. If not, the
LCD can start flickering and the blue component of the pixel color can disappear for short time periods
(= the flickering). If the picture is mainly blue it will look like a black row on the display. If other colors
are dominating on the picture shown, it can also look like yellow lines (white minus block color
component result in a yellow color).
The reason for this problem is that the I2C interface of the MIC2555 USB OTG transceiver is
connected to the two MSB signals of the blue color component. Even though the pixel data is very
much out of spec for the I2C interface, the MIC2555 reacts on some sequences and start driving the
MSB signal low, which is the flickering that is seen. The solution is to remove resistor R163.
The LCD interface and the USB OTG transceiver cannot be used at the same time on the OEM Base
Board.
R239 – add 100nF
capacitor in parallel
Speaker