PIC18F47J53 Datasheet, PDF (417/586 Pages) Microchip Technology – 28/44-Pin, High-Performance USB Microcontrollers with nanoWatt XLP Technology

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25.2 Voltage Reference Accuracy/Error
The full range of voltage reference cannot be realized
due to the construction of the module. The transistors
on the top and bottom of the resistor ladder network
(see Figure 25-1) keep CVREF from approaching the
reference source rails. The voltage reference is derived
from the reference source; therefore, the CVREF output
changes with fluctuations in that source. The tested
absolute accuracy of the voltage reference can be
found in Section 31.0 “Electrical Characteristics”.
25.3 Connection Considerations
The voltage reference module operates independently
of the comparator module. The output of the reference
generator may be connected to the RA2 pin if the
CVROE bit is set. Enabling the voltage reference out-
put onto RA2 when it is configured as a digital input will
increase current consumption. Connecting RA2 as a
digital output with CVRSS enabled will also increase
current consumption.
The RA2 pin can be used as a simple D/A output with
limited drive capability. Due to the limited current drive
capability, a buffer must be used on the voltage
reference output for external connections to VREF. See
Figure 25-2 for an example buffering technique.
25.4 Operation During Sleep
When the device wakes up from Sleep through an
interrupt or a Watchdog Timer time-out, the contents of
the CVRCON register are not affected. To minimize
current consumption in Sleep mode, the voltage
reference should be disabled.
25.5 Effects of a Reset
A device Reset disables the voltage reference by
clearing bit, CVREN (CVRCON<7>). This Reset also
disconnects the reference from the RA2 pin by clearing
bit, CVROE (CVRCON<6>) and selects the high-voltage
range by clearing bit, CVRR (CVRCON<5>). The CVR
value select bits are also cleared.
FIGURE 25-2:
COMPARATOR VOLTAGE REFERENCE OUTPUT BUFFER EXAMPLE
PIC18F47J53
CVREF
Module
R⁽¹⁾
Voltage
Reference
Output
Impedance
RA2
+
–
CVREF Output
Note 1: R is dependent upon the Comparator Voltage Reference Configuration bits, CVRCON<5> and CVRCON<3:0>.
TABLE 25-1: REGISTERS ASSOCIATED WITH COMPARATOR VOLTAGE REFERENCE
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
CVRCON
CVREN CVROE CVRR CVRSS CVR3
CVR2
CVR1
CVR0
CM1CON
CON
COE
CPOL EVPOL1 EVPOL0 CREF
CCH1
CCH0
CM2CON
CON
COE
CPOL EVPOL1 EVPOL0 CREF
CCH1
CCH0
CM3CON
CON
COE
CPOL EVPOL1 EVPOL0 CREF
CCH1
CCH0
TRISA
ANCON0
TRISA7 TRISA6 TRISA5
—
PCFG7⁽¹⁾ PCFG6⁽¹⁾ PCFG5⁽¹⁾ PCFG4
TRISA3
PCFG3
TRISA2
PCFG2
TRISA1
PCFG1
TRISA0
PCFG0
Legend: — = unimplemented, read as ‘0’, r = reserved. Shaded cells are not used with the comparator voltage
reference.
Note 1: These bits are only available on 44-pin devices.
 2010 Microchip Technology Inc.
DS39964B-page 417