PIC16F753 datasheet(168/230 Pages) MICROCHIP

168 / 230 page

PIC16F753/HV753

DS40001709C-page 168

 2013-2015 Microchip Technology Inc.

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

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

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).

Feedback

VDD

VSS

CBYPASS

RSER

VUNREG

ISUPPLY

ISHUNT

ILOAD

Device

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

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