PIC16F753 Datasheet, PDF (181/238 Pages) Microchip Technology – 14/16-Pin, Flash-Based 8-Bit CMOS Microcontrollers

20.0 SHUNT REGULATOR
(PIC16HV753 ONLY)
The PIC16HV753 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).
20.1 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 20-1 for voltage regulator schematic.
FIGURE 20-1:
SHUNT REGULATOR
VUNREG
ISUPPLY
RSER
CBYPASS
ISHUNT
ILOAD
VDD
Feedback
VSS
Device
PIC16F753/HV753
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 20-1.
EQUATION 20-1: RSER LIMITING RESISTOR
RMAX =
(VUMIN - 5V)
1.05 • (1 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
20.2 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 PIC16HV753 devices.
The shunt regulator will still consume current when
below operating voltage range for the shunt regulator.
20.3 Design Considerations
For more information on using the shunt regulator and
managing current load, see Application Note AN1035,
“Designing with HV Microcontrollers” (DS01035).
 2013 Microchip Technology Inc.
Preliminary
DS40001709A-page 181