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SK-MB9EF120-002,-003
Hardware
Headers are connected to each voltage-rail to allow measuring the voltages. They should not be used
to power custom electronics. Each stage provides a header connected to connect to the
corresponding domain. Care must be taken when connecting to the 1V2-domain as noise on this rail
will have much more impact on this rail due to the low absolute voltage.
2.2.1 Input Stage
The power-supply connector is a standard DC-plug for an AC-adapter. Allowed input voltage ranges
from 9 to 12V, the adaptor should have a minimum power-rating of 12W (1A @ 12V).
After the power-switch, a reverse-voltage protection diode (D2) and an overvoltage protection device
(D3) follow. The latter suppresses/damps high voltage surges from the AC-adaptor which would
otherwise pass the following inductor and capacitors.
The inductor (L4) filters noise generated on-board, before it reaches the supply-cable which presents
a good antenna for EMI. Filtering incoming noise is a bonus.
2.2.2 I/O Supplies
The 5V0 and 3V3 supplies are generated from the input-rail by two step-down switching regulators,
each fixed to the desired output-voltage. As with all switching regulators, the designs are critical in
terms of switching noise.
Each regulator provides up to 3A to its rail.
2.2.3 MCU Core supply
The 1V2 supply for the MCU core is generated by a switching regulator module which includes the
inductor. It provides up to 3A to the rail.
2.2.4 Supply-Rail Monitor LEDs
Each supply-rail has its own LED-indicator. For the 1V2 rail, the LED is driven from the 3V3 rail, but
switched from the 1V2 rail.
All three rails are monitored for drops by a system-voltage supervisor (U6).
2.2.5 Power distribution
The three stabilized voltages drive the various MCU power-domains either directly (single-voltage
domains MCU_VDD, MCU_VDP3) or through a 3-pin jumper (dual-voltage domains VDP5, DVCC).
Additionally, there is a jumper before each domain's EMI-filter to allow injection of external supply or
measuring the current-consumption of the domain.
2.3 Reset
Board-Reset can be generated by basically two sources. Both are connected to the system-reset
which includes the microcontroller's reset-signal. Both sources can be disconnected from the reset-
net by separate jumpers, thus excluding them from generating the reset-signal.
U6 generates the reset to the MCU and all other devices if one of the three system-voltages fails
(System Voltage Supervisor). It also monitors a push-button, generating a short reset-pulse (~100µs)
if this reset-button is pressed shortly. If the button is held pressed for some seconds, the reset-line will
be permanently asserted until the button is released. Caution: the SVS monitors the on-board
generated voltages, not the MCU power-domains. If any of the domains is supplied externally, it is left
to the user to provide a proper reset signal.
The second source of reset is the debugging-connectors (JTAG or TRACE). This source can also be
disconnected from the internal net.
A slight problem arises with the SVS output-signal having an internal current-source (pull-up) from the
3V3-domain. The MCU reset-input is located in the VDP5-domain, so an open-drain-driver (non-
inverting) is used which buffers the signal and has a pull-up resistor to VDP5 at the output, generating
RST_X_VDP5.
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© Fujitsu Semiconductor Europe GmbH
UG-9E0010-11
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