MXED401
CIRCUIT DESCRIPTION
Voltage Regulator
This product may be operated from supplies as low as 2.5 Volts. The output drive transistors require
a voltage of 5.0 volts to 11.0 volts on the XIN pin to assure proper circuit operation. This bias voltage
may be developed on the chip or provided by the system designer. When XIN is provided externally,
the REN (Regulator ENable) pin is held low, and the FLYHI/FLYLO pins are left unconnected.
Systems lacking an available bias may use the on chip voltage regulator. The circuit is enabled by
forcing REN high (to VDD1). This will cause an on-chip oscillator/charge pump circuit to operate
continuously and output a somewhat regulated 5 volts at pin REG5V. A capacitor (CFLY=0.1uF) is
connected between pins FLYHI and FLYLO. A storage capacitor (CHOLD=1.0uF) is required on
REG5V. The XIN input is then connected to the REG5V output. The charge pump is capable of
driving 18 XIN loads so generally only one or two circuits are used as regulator sources. In systems
where more than one regulator circuit is enabled it is forbidden to short their respective HOLD
capacitors. Enabling the regulator causes an additional DC current of 65uA (130 uA maximum) to
flow from VDD1 to VSS1.
FIGURE 2 - REGULATOR BLOCK DIAGRAM
FIGURE 3 - EXAMPLE USING ON CHIP REGULATOR
FIGURE 4 - EXAMPLE USING EXTERNAL BIAS
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