DSPIC33FJ12MC201TESS datasheet(208/304 Pages) MICROCHIP

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dsPIC33FJ12MC201/202

DS70265E-page 208

21.2

On-Chip Voltage Regulator

All of the dsPIC33FJ12MC201/202 devices power their

core digital logic at a nominal 2.5V. This can create a

conflict for designs that are required to operate at a

higher typical voltage, such as 3.3V. To simplify system

design, all devices in the dsPIC33FJ12MC201/202

family incorporate an on-chip regulator that allows the

device to run its core logic from VDD.

The regulator provides power to the core from the other

VDD pins. When the regulator is enabled, a low-ESR

(less than 5 ohms) capacitor (such as tantalum or

ceramic) must be connected to the VCAP pin

(Figure 21-1). This helps to maintain the stability of the

regulator. The recommended value for the filter capac-

itor is provided in Table 24-13 located in Section 24.1

“DC Characteristics”

On a POR

, it takes approximately 20 μs for the on-chip

voltage regulator to generate an output voltage. During

this time, designated as TSTARTUP, code execution is

disabled. TSTARTUP is applied every time the device

resumes operation after any power-down.

FIGURE 21-1:

CONNECTIONS FOR THE

ON-CHIP VOLTAGE

REGULATOR(1,2,3)

21.3

Brown-out Reset (BOR)

The Brown-out Reset (BOR) module is based on an

internal voltage reference circuit that monitors the reg-

ulated supply voltage VCAP. The main purpose of the

BOR module is to generate a device Reset when a

brown-out condition occurs. Brown-out conditions are

generally caused by glitches on the AC mains (for

example, missing portions of the AC cycle waveform

due to bad power transmission lines, or voltage sags

due to excessive current draw when a large inductive

load is turned on).

A BOR generates a Reset pulse, which resets the

device. The BOR selects the clock source, based on

the device Configuration bit values (FNOSC<2:0> and

POSCMD<1:0>).

If an oscillator mode is selected, the BOR activates the

Oscillator Start-up Timer (OST). The system clock is

held until OST expires. If the PLL is used, the clock is

held until the LOCK bit (OSCCON<5>) is ‘1’.

Concurrently, the PWRT time-out (TPWRT) is applied

before the internal Reset is released. If TPWRT = 0 and

a crystal oscillator is being used, then a nominal delay

of TFSCM = 100 is applied. The total delay in this case

is TFSCM.

The BOR Status bit (RCON<1>) is set to indicate that a

BOR has occurred. The BOR circuit continues to oper-

ate while in Sleep or Idle modes and resets the device

should VDD fall below the BOR threshold voltage.

Note:

It is important for low-ESR capacitors to

be placed as close as possible to the VCAP

pin.

Note

These are typical operating voltages. Refer

to Section TABLE 24-13: “Internal Volt-

age Regulator Specifications”

located in

Section 24.1 “DC Characteristics”

for the

full operating ranges of VDD and VCAP.

It is important for low-ESR capacitors to be

placed as close as possible to the VCAP

pin.

Typical VCAP pin voltage = 2.5V when

VDD ≥ VDDMIN.

VDD

VCAP

VSS

dsPIC33F

3.3V

CEFC

10 µF

Tantalum

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