1-6
USB232 Converter User Guide
1.6.5 1.4.6Automatic XON/XOFF Software Flow Control
When software flow control is enabled, the V1410 compares the receive data characters with the
programmed Xon or Xoff characters. If the received character matches the programmed Xoff character, the
V1410 will halt transmission as soon as the current character has completed transmission. Data transmission
is resumed when a received character matches the Xon character.
1.7 Schematic
The schematic can be broken into functional sections.
1.7.1 USB Soft Connect
The soft connect circuit allows the unit to be connected without a large inrush current. Q1 is a P-channel
MOSFET rated at 12V, 4.1A. The gate charge is controlled by C1 and R1. As the gate charge voltage is
increased the channel opens to allow USB +5VDC on J1, pin 1 to be applied to other circuits.
USB data is supplied on J1, pins 2 and 3.
Figure 3-Soft Start
1.7.2 Transient Suppressor
A USB Port Transient Suppressor (U2) circuit has been added to the USB data lines. The SN75240 is a dual
transient voltage suppressor designed to provide electrical noise transient protection to Universal Serial Bus
(USB) full
−
speed ports.
Any cabled I/O can be subjected to electrical noise transients from various sources. These noise transients
can cause damage to the USB transceiver and/or the USB ASIC if they are of sufficient magnitude and
duration. USB ports are typically implemented in 3-V or 5-V digital CMOS with very limited ESD
protection. The SN75240 can significantly increase the port ESD protection level and reduce the risk of
damage to the circuits of the USB port.
Figure 4-USB Transient Suppressor
