PIC18F45K80-I/PT Microchip Technology, PIC18F45K80-I/PT Datasheet - Page 255

• Manufacturer Part Number: PIC18F45K80-I/PT
• Description: MCU PIC 32KB FLASH 44TQFP
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F45K80-I/PT

• Core Size: 8-Bit
• Program Memory Size: 32KB (16K x 16)
• Peripherals: Brown-out Detect/Reset, LVD, POR, PWM, WDT
• Core Processor: PIC
• Speed: 64MHz
• Connectivity: ECAN, I²C, LIN, SPI, UART/USART
• Number Of I /o: 35
• 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 11x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP
• Controller Family/series: PIC18
• Ram Memory Size: 4KB
• Cpu Speed: 16MIPS
• No. Of Pwm Channels: 5
• Embedded Interface Type: I2C, SPI, USART
• Processor Series: PIC18F45K80
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 1 KB
• Interface Type: I2C, SPI, USART
• Maximum Clock Frequency: 64 MHz
• Number Of Programmable I/os: 35
• Number Of Timers: 5
• Operating Supply Voltage: 1.8 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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