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71M6513/71M6513H Demo Board User’s Manual
Page: 60 of 112
©
2005-2006 TERIDIAN Semiconductor Corporation
Revision 5.6
If inputs higher than 3.6V are expected at the RX pin, e.g. when interfacing to 5V-based driving circuitry such as
RS-232 transceivers/receivers, TTL or CMOS logic, a resistor attenuator should be used in order to restrict the
RX input voltage.
Figure 2-17 shows the recommended resistor network consisting of R1 (17k
Ω
) and R2 (33k
Ω
). This network
scales the input voltage V
IN
of 5.5V to 3.6V, and an input voltage of 2.5V will be scaled to 1.6V. For the low
voltage level, V
IN
voltages below 1.2V will be scaled to 0.8V. The maximum current at 5.5V input voltage is
5.5V/(50k
Ω
) + I
IH
= 110µA + 1µA = 111µA.
Figure 2-17: Resistor Network for RX
2.4.8 CONNECTING THE V3 PIN
If not used for sensing or measuring purposes, the V3 pin should be either left unconnected (floating) or
connected to the VREF pin.
RX
R1 = 17k
Ω
R2 = 33k
Ω
71M6513
V
IN
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