PIC18F258-ESLASHLSQTP datasheet(261/402 Pages) MICROCHIP

261 / 402 page

DS41159E-page 259

PIC18FXX8

23.0

LOW-VOLTAGE DETECT

In many applications, the ability to determine if the

device voltage (VDD) is below a specified voltage level

is a desirable feature. A window of operation for the

application can be created, where the application

software can do “housekeeping tasks” before the

device voltage exits the valid operating range. This can

be done using the Low-Voltage Detect module.

This module is a software programmable circuitry,

where a device voltage trip point can be specified.

When the voltage of the device becomes lower than the

specified point, an interrupt flag is set. If the interrupt is

enabled, the program execution will branch to the

interrupt vector address and the software can then

respond to that interrupt source.

The Low-Voltage Detect circuitry is completely under

software control. This allows the circuitry to be “turned

off” by the software which minimizes the current

consumption for the device.

Figure 23-1 shows a possible application voltage curve

(typically for batteries). Over time, the device voltage

decreases. When the device voltage equals voltage VA,

the LVD logic generates an interrupt. This occurs at

time TA. The application software then has the time,

until the device voltage is no longer in valid operating

range, to shutdown the system. Voltage point VB is the

minimum valid operating voltage specification. This

occurs at time TB. The difference TB – TA is the total

time for shutdown.

The block diagram for the LVD module is shown in

Figure 23-2. A comparator uses an internally gener-

ated reference voltage as the set point. When the

selected tap output of the device voltage crosses the

set point (is lower than), the LVDIF bit is set.

Each node in the resistor divider represents a “trip point”

voltage. The “trip point” voltage is the minimum supply

voltage level at which the device can operate before the

LVD module asserts an interrupt. When the supply

voltage is equal to the trip point, the voltage tapped off of

the resistor array is equal to the internal reference

voltage generated by the voltage reference module. The

comparator then generates an interrupt signal, setting

the LVDIF bit. This voltage is software programmable to

any one of 16 values (see Figure 23-2). The trip point is

selected

programming

the

LVDL3:LVDL0

bits

(LVDCON<3:0>).

FIGURE 23-1:

TYPICAL LOW-VOLTAGE DETECT APPLICATION

Time

VA = LVD trip point

VB = Minimum valid device

operating voltage

Legend:

PIC18F258-E/LSQTP Datasheet(PDF) 261 Page - Microchip Technology

PIC18F258-E/LSQTP Datasheet(HTML) 261 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL