User Manual

E a s y P I C v 8 M a n u a l
P A G E 9
The next PSU stage uses two MIC28511, synchronous step-down (buck) regulators,
capable of providing up to 3A at their output. The MIC28511 IC utilizes the HyperSpeed
Control® and HyperLight Load® architectures, providing an ultra-fast transient
response and high effi ciency for light loads. Each of the two buck regulators is used
to supply power to the corresponding power supply rail (3.3V and 5V), throughout the
entire development board and connected peripherals.
Voltage reference
The PSU is able to provide a very accurate, programmable voltage reference (VREF) (5)
in the range from 0V to 4.096V. VREF is very useful for many diff erent applications
including A/D and D/A converters, comparators, etc.
The programmable VREF design is based on several diff erent ICs produced by
Microchip: the MCP1501, a high-precision buff ered voltage reference IC is used to
provide a very precise VREF of 4.096V for the MCP4726, a 12-bit D/A converter (DAC)
with integrated EEPROM. The MCP4726 DAC is controlled and programmed by the
CODEGRIP module, over the I2C interface. Finally, the MCP606, a single rail-to-rail
operational amplifi er is used to provide an additional buff ering at the output. By using
a 4-pole DIP switch (6) located in the VREF section of the development board, it is
possible to route VREF to four diff erent MCU pins:
ON (up): connects VREF to the MCU pins (RA0, RA1, RA3, and RC0)
OFF (down): disconnects VREF from the MCU pins (RA0, RA1, RA3, and RC0)
Programming voltage
Not all PIC MCU devices support low voltage programming. Therefore, the PSU module
has to provide the required high voltage (VPP) for the programming of such devices.
The VPP is controlled by the CODEGRIP module automatically, it depends on the
programmed MCU and can’t be modifi ed by the user. To provide a suffi cient voltage
level, the MIC2250, a high-effi ciency, low EMI boost regulator is used. It is used to
provide 14V for the operational amplifi er circuit composed of a dual operational
amplifi er, labeled as MCP6H02T, and produced by Microchip. This circuit has a fi xed
gain, allowing the CODEGRIP programmer/debugger module to reach up to 14V for
the high-voltage programming of various PIC MCU devices.
E a s y P I C v 8 M a n u a l
P A G E 9
P O W E R S U P P L Y
6
5
Figure 1: Power supply unit view
N O T EIn order to protect host MCU and development board, VREF values higher then
3.3V can only be set if the board voltage is previously set to 5V.