Datasheet

PIC24HJ12GP201/202
DS70282E-page 170 © 2007-2011 Microchip Technology Inc.
19.2 On-Chip Voltage Regulator
All of the PIC24HJ12GP201/202 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 PIC24HJ12GP201/202 family
incorporate an on-chip regulator that allows the device
to run its core logic from V
DD.
The regulator provides power to the core from the other
V
DD pins. When the regulator is enabled, a low-ESR
(less than 5 ohms) capacitor (such as tantalum or
ceramic) must be connected to the V
CAP pin
(Figure 19-1). This helps to maintain the stability of the
regulator. The recommended value for the filter capac-
itor is provided in Table 22-13 located in Section 22.1
“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 T
STARTUP, code execution is
disabled. TSTARTUP is applied every time the device
resumes operation after any power-down.
FIGURE 19-1: CONNECTIONS FOR THE
ON-CHIP VOLTAGE
REGULATOR
(1,2,3)
19.3 BOR: Brown-out Reset (BOR)
The Brown-out Reset module is based on an internal
voltage reference circuit that monitors the regulated
voltage V
CAP. 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 por-
tions of the AC cycle waveform due to bad power trans-
mission 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) will be
applied before the internal Reset is released. If
TPWRT = 0 and a crystal oscillator is being used, 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 V
DD fall below the BOR threshold voltage.
Note: It is important for low-ESR capacitors to
be placed as close as possible to the V
CAP
pin.
Note 1: These are typical operating voltages. Refer
to Table 22-13: “Internal Voltage Regulator
Specifications” located in Section 22.1 “DC
Characteristics” for the full operating
ranges of V
DD and VCAP.
2: It is important for low-ESR capacitors to be
placed as close as possible to the V
CAP
pin.
3: Typical V
CAP pin voltage = 2.5V when
V
DD ≥ VDDMIN.
V DD
V CAP
V SS
PIC24H
C EFC
3.3V
10 µF
Tantalum