AN158 Datasheet, PDF (1/3 Pages) Macronix International – Serial-Data Interface Chip Supplies Bipolar Voltages

INTERFACE CIRCUITS
Jul 09, 1998
Serial-Data Interface Chip Supplies Bipolar
Voltages
Some of the interface ICs currently available for serial-data transmission not only operate
from low VCC levels (5V or 3.3V); they also generate bipolar dc voltages (±6.5V to ±10V) to
support the minimum driver-output levels as specified by EIa/TIa-232. With care, you can
steal useful amounts of power from these voltage rails without interfering with the IC's
operation.
In Figure 1, the IC's switch-mode controller operates with an external inductor, two diodes,
and two capacitors to produce ±6.5V. FETs Q1 and Q2 ensure start-up for the circuit by
disconnecting the load until these switch-mode supply voltages are present. Note that Q1
must be a logic-level device.