PIC18F25K80T-I/MM Microchip Technology, PIC18F25K80T-I/MM Datasheet - Page 255
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PIC18F25K80T-I/MM
Manufacturer Part Number
PIC18F25K80T-I/MM
Description
ECAN, 32KB Flash, 4KB RAM, 16 MIPS, 12-bit ADC, CTMU 28 QFN-S 6x6mm T/R
Manufacturer
Microchip Technology
Series
PIC® XLP™ 18Fr
Datasheet
1.PIC18F25K80-ISO.pdf
(628 pages)
Specifications of PIC18F25K80T-I/MM
Core Processor
PIC
Core Size
8-Bit
Speed
64MHz
Connectivity
ECAN, I²C, LIN, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, LVD, POR, PWM, WDT
Number Of I /o
24
Program Memory Size
32KB (16K x 16)
Program Memory Type
FLASH
Eeprom Size
1K x 8
Ram Size
3.6K x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 5.5 V
Data Converters
A/D 8x12b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
*
Processor Series
PIC18F25K80
Core
PIC
Data Bus Width
8 bit
Data Ram Size
3648 B
Interface Type
I2C, SPI
Maximum Clock Frequency
64 MHz
Number Of Programmable I/os
24
Number Of Timers
5
Operating Supply Voltage
1.8 V to 5.5 V
Maximum Operating Temperature
+ 125 C
Mounting Style
SMD/SMT
Minimum Operating Temperature
- 40 C
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
PIC18F25K80T-I/MM
Manufacturer:
MICROCHIP
Quantity:
3 000
- Current page: 255 of 628
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18.7
The constant current source provided by the CTMU
module can be used for low-cost temperature
measurement by exploiting a basic property of com-
mon and inexpensive diodes. An on-chip temperature
sense diode is provided on ADC Channel 29 to further
simplify design and cost.
18.7.1
We can show that the forward voltage ( V
junction, such as a diode, is an extension of the
equation for the junction’s thermal voltage:
where k is the Boltzmann constant (1.38 x 10
T is the absolute junction temperature in kelvin, q is the
electron charge (1.6 x 10
applied to the diode and I
saturation current, which varies between devices.
Since k and q are physical constants, and I
for the device, this only leaves T and I
variables. If I
tion that V
term of the equation will always be negative, the temper-
ature will be negatively proportional to V
words, as temperature increases, V
By using the CTMU’s current source to provide a
constant I
temperature by measuring the V
18.7.2
To implement this theory, all that is needed is to con-
nect a regular junction diode to one of the microcon-
troller’s A/D pins
multiplexer is shared by the CTMU and the ADC.
EXAMPLE 18-5:
2011 Microchip Technology Inc.
// Initialize CTMU
CTMUICON = 0x03;
CTMUCONHbits.CTMUEN = 1;
CTMUCONLbits.EDG1STAT = 1;
// Initialize ADC
ADCON0 = 0xE5;
ADCON1 = 0x00;
ADCON2 = 0xBE;
ADCON0bits.GO = 1;
while(ADCON0bits.G0);
Temp = ADRES;
Note:
Measuring Temperature
with the CTMU
F
F
The temperature diode is not calibrated or standardized; the user must calibrate the diode to their application.
will vary as a function of T . As the natural log
BASIC PRINCIPAL
, it becomes possible to calculate the
IMPLEMENTATION
F
is held constant, it follows from the equa-
V
F
=
(Figure
kT
ROUTINE FOR TEMPERATURE MEASUREMENT USING INTERNAL DIODE
q
-19
S
1n 1 –
is the diode’s characteristic
C), I
18-2). The A/D channel
(
F
F
is the forward current
across the diode.
I
I
F
S
F
)
decreases.
F
as independent
S
is a constant
F
F
) of a P-N
. In other
-23
// Enable ADC and connect to Internal diode
//Right Justified
// Start conversion
// Read ADC results (inversely proportional to temperature)
J K
Preliminary
-1
),
PIC18F66K80 FAMILY
To perform a measurement, the multiplexer is config-
ured to select the pin connected to the diode. The
CTMU current source is then turned on and an A/D
conversion is performed on the channel. As shown in
the equivalent circuit diagram, the diode is driven by
the CTMU at I
measured by the ADC. A code snippet is shown in
Example
FIGURE 18-4:
Simplified Block Diagram
Equivalent Circuit
18-5.
F
. The resulting V
I
F
PIC
Current Source
MUX
®
V
F
CTMU TEMPERATURE
MEASUREMENT CIRCUIT
Microcontroller
A/D Converter
CTMU
V
F
F
CTMU
A/D
across the diode is
DS39977C-page 255
ADC
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