Datasheet

PIC16F785/HV785
DS41249E-page 126 © 2008 Microchip Technology Inc.
16.0 VOLTAGE REGULATOR
The PIC16HV785 includes a permanent internal 5 volt
(nominal) shunt regulator in parallel with the V
DD pin.
This eliminates the need for an external voltage regula-
tor in systems sourced by an unregulated supply. All
external devices connected directly to the V
DD pin will
share the regulated supply voltage and contribute to
the total V
DD supply current (ILOAD).
16.1 Regulator Operation
The regulator operates by maintaining a constant
voltage at the V
DD pin by adjusting the regulator shunt
current in response to variations of the V
DD supply load
and the unregulated supply voltage. The regulator
behaves like a fully compensated Zener diode. (See
Figure 16-1).
FIGURE 16-1: REGULATOR
An external current limiting resistor, RSER, located
between the unregulated supply, V
UNREG, and the VDD
pin, drops the difference in voltage between VUNREG
and VDD. RSER must be between RMAX and RMIN as
defined by Equation 16-1.
EQUATION 16-1: RSER LIMITING RESISTOR
16.2 Regulator Precautions
The total VDD load current variation must be less than
46 mA so that it falls within the voltage regulator shunt
current dynamic range. If the load current rises above
the expected maximum, the regulator will be starved for
current and go out of regulation causing V
DD to drop.
Since the regulator uses the band gap voltage as the
regulated voltage reference, the VR voltage reference
is permanently enabled in the PIC16HV785 device.
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VUNREG
RSER
VDD
To other circuitry
PIC16HV785
Voltage
Regulator
RMAX =
(VUMIN - VDD) • 1000
1.05 • (4 MA + ILOAD)
RMIN =
(VUMIN - VDD) • 1000
0.95 • (50 MA)
Where:
R
MAX = maximum value of RSER (ohms)
R
MIN = minimum value of RSER (ohms)
VU
MIN = minimum value of VUNREG
VUMAX = maximum value of VUNREG
VDD = regulated voltage (5V nominal)
I
LOAD = maximum expected load current in mA
including I/O pin currents and external
circuits connected to VDD.
1.05 = compensation for +5% tolerance of R
SER
0.95 = compensation for -5% tolerance of RSER