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PIC12F752 Datasheet(PDF) 155 Page - Microchip Technology |
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PIC12F752 Datasheet(HTML) 155 Page - Microchip Technology |
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155 / 204 page  2011 Microchip Technology Inc. Preliminary DS41576A-page 155 PIC12F752/HV752 18.0 SHUNT REGULATOR (PIC12HV752 ONLY) The PIC12HV752 devices include a permanent internal 5 volt (nominal) shunt regulator in parallel with the VDD pin. This eliminates the need for an external voltage regulator in systems sourced by an unregulated supply. All external devices connected directly to the VDD pin will share the regulated supply voltage and contribute to the total VDD supply current (ILOAD). 18.1 Regulator Operation A shunt regulator generates a specific supply voltage by creating a voltage drop across a pass resistor RSER. The voltage at the VDD pin of the microcontroller is monitored and compared to an internal voltage refer- ence. The current through the resistor is then adjusted, based on the result of the comparison, to produce a voltage drop equal to the difference between the supply voltage VUNREG and the VDD of the microcontroller. See Figure 18-1 for voltage regulator schematic. FIGURE 18-1: SHUNT REGULATOR An external current limiting resistor, RSER, located between the unregulated supply, VUNREG, and the VDD pin, drops the difference in voltage between VUNREG and VDD. RSER must be between RMAX and RMIN as defined by Equation 18-1. EQUATION 18-1: RSER LIMITING RESISTOR 18.2 Regulator Considerations The supply voltage VUNREG and load current are not constant. Therefore, the current range of the regulator is limited. Selecting a value for RSER must take these three factors into consideration. Since the regulator uses the band gap voltage as the regulated voltage reference, this voltage reference is permanently enabled in the PIC12HV752 devices. The shunt regulator will still consume current when below operating voltage range for the shunt regulator. 18.3 Design Considerations For more information on using the shunt regulator and managing current load, see Application Note AN1035, “Designing with HV Microcontrollers” (DS01035). Feedback VDD VSS CBYPASS RSER VUNREG ISUPPLY ISHUNT ILOAD Device RMAX = (VUMIN - 5V) 1.05 • (4 MA + ILOAD) RMIN = (VUMAX - 5V) 0.95 • (50 MA) Where: RMAX = maximum value of RSER (ohms) RMIN = minimum value of RSER (ohms) VUMIN = minimum value of VUNREG VUMAX = maximum value of VUNREG VDD = regulated voltage (5V nominal) ILOAD = maximum expected load current in mA including I/O pin currents and external circuits connected to VDD. 1.05 = compensation for +5% tolerance of RSER 0.95 = compensation for -5% tolerance of RSER |
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