User Manual

P A G E 11
mikromedia 5 for STM32 CAPACITIVE U S E R M A N U A L
2.1 Detailed description
POWER SUPPLY
The PSU has a very demanding task of providing power for the host MCU
and all the peripherals onboard, as well as for the externally connected
peripherals. One of the key requirements is to provide enough current,
avoiding the voltage drop at the output. Also, the PSU must be able to
support multiple power sources with different nominal voltages, allowing
switching between them by priority. The PSU design, based on a set of
high-performance power switching ICs produced by Microchip, ensures a
very good quality of the output voltage, high current rating, and reduced
electromagnetic radiation.
At the input stage of the PSU, the MIC2253, a high-efficiency boost
regulator IC with overvoltage protection ensures that the voltage input at
the next stage is well-regulated and stable. It is used to boost the voltage
of low-voltage power sources (a Li-Po/Li-Ion battery and USB), allowing
the next stage to deliver well-regulated 3.3V and 5V to the development
board. A set of discrete components are used to determine if the input
power source requires a voltage boost. When multiple power sources are
connected at once, this circuitry is also used to determine the input priority
level: externally connected 12V PSU, power over USB, and the Li-Po/Li-Ion
battery. The transition between available power sources is designed to
provide uninterrupted operation of the development board.
The next PSU stage uses two MIC28511, synchronous step-down (buck)
regulators, capable of providing up to 3A. The MIC28511 IC utilizes the
HyperSpeed Control
®
and HyperLight Load
®
architectures, providing an
ultra-fast transient response and high light-load efficiency. 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.
The MCP1501, a high-precision buffered voltage reference from Microchip
is used to provide a very precise voltage reference with no voltage drift. It
can be used for various purposes: the most common uses include voltage
references for A/D converters, D/A converters, and comparator peripherals
on the host MCU. The MCP1501 can provide up to 20mA, limiting its use
exclusively to voltage comparator applications with high input impedance.
Depending on the specific application, either 3.3V from the power rail,
or 2.048V from the MCP1501 can be selected. An onboard SMD jumper
labeled as REF SEL offers two voltage reference choices:
∫ REF: 2.048V from the high-precision voltage reference IC
∫ 3V3: 3.3V from the main power supply rail
2.2 Voltage reference