Microchip Technology MCP1630 Manual de usuario descargar pdf (Pagina 13)

Installation and Operation

2.3.1.2 APPLYING LOAD TO MCP1630 AUTOMOTIVE INPUT TRIPLE OUTPUT

CONVERTER DEMO BOARD

A variable resistive load can be used to verify the line regulation, load regulation and

cross regulation. The load resistance for the three outputs can be connected

accordingly. Note that the currents should not exceed the maximum current limit of

individual outputs i.e: 1.2A (maximum) for V

OUT1

, 600 mA (maximum) for V

OUT2

and

150 mA (maximum) for V

OUT3

, respectively. The load resistance is connected between

the test points TP3 and TP4 for V

OUT1

, between test points TP7 and TP8 for V

OUT2

and

between test points TP5 and TP6 for V

OUT3

. To measure the output voltage, connect

the common point of multimeter to TP3 and the positive terminal to TP4 for V

OUT1

. Sim-

ilarly, to measure the output voltages of V

OUT2

and V

OUT3

, connect the common point

of multimeter to TP8 for V

OUT2

and TP6 for V

OUT3

and the positive terminal to TP7 for

OUT2

and TP5 for V

OUT3

The load regulation and cross regulation can be verified by varying the load from 50%

to 100%, with different combination of loads on all the outputs. Similarly, by varying the

line voltage from 6.5V to 40V and checking the output voltage, the line regulation can

be calculated.

Evaluating the Application

The best way to evaluate the MCP1630 Automotive Input Triple Output Converter

Demo Board is to dig into the circuit. Measure voltages and currents with a DVM and

probe the board with an oscilloscope.

The firmware program in the PIC12F683 can also be edited to modify the operation of

the application.

Firmware

The PIC12F683 comes pre programmed with firmware to operate the system as

described above. The file listing and firmware flow diagram are shown in Appendix

C. “Demo Board Firmware”.

The program is fairly simple and straight forward. There is an initialization routine at the

beginning of the program.

The internal oscillator clock is set to 8 MHz.The TRISIO is configured to set GP2

(Oscillator pulses to the MCP1630) and GP4 (V

REF

Voltage to MCP1630) as an output

port and GP3 (Switch SW1) as Input Port.The OPTION register is configured to

wake-up on Port pin change of GP3.

The Capture/Compare/PWM (CCP) module contains a 16-bit register which can

operate in PWM mode. The PWM period can be calculated by writing to the PR2

CCP1CON <5:4> bits. Up to 10-bit resolution is available. The CCPR1L contains the

eight MSbs and the CCP1CON <5:4> contains the two LSbs. This 10-bit value is

represented by CCPR1L:CCP1CON<5:4>. The switching frequency is set to 250 kHz.

Upon powering on, the processor enters into SLEEP mode after the ports are initialized

and registers configured. The processor wakes-up from SLEEP mode, if the Switch

SW1 on GP3 is pressed.

Once the processor is on after the switch SW1 is pressed, the three output voltages of

3.3V, 1.2V and 4.7V are generated by set by generating V

REF

voltage and the PWM

signal. TMR0 is configured to generate the V

REF

voltage.

During normal operation, a subsequent pressing of switch SW1 will make the converter

to go into SLEEP mode.

The switch SW1 is used to perform a simple ON/OFF operation.

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