UM1574
Hardware and layout
Doc ID 023645 Rev 1
11/48
4.1.3 Power
supply
The power supply is provided by the host PC through the dual type A to mini-B USB cable or
by an external V
BAT
power supply (12 Vdc typical
,
14 Vdc max).
One dual type A to mini-B USB is needed to provide the current required by the STM8AF
and STM8AL boards when they are connected together.
Reminder:
First connect the dual type A on the PC side (both type A connectors must be
plugged in) then connect the mini-B USB to one of the STM8Ax boards.
When the STM8AF board is connected to the STM8AL board, different schemes are
possible:
●
The USB cable is used to simply provide the power supply to the STM8A-DISCOVERY.
In that case, it can be connected either to the STM8AF or STM8AL board side.
●
While programming/debugging the STM8AF or STM8AL board with your PC, the USB
cable must be placed on the appropriate side of the board depending on which board is
being debugged
(see
Figure 3
and
Figure 4
).
●
If no programming/debugging operations are needed (no PC connected) or if a larger
amount of current is required (higher than 200 mA @5 V), then the power supply must
be wired between the V
BAT
and GND pins of the STM8AF or STM8AL board. V
BAT
is
indeed internally distributed through the two boards. Therefore, V
BAT
can be wired
indifferently on the STM8AF or STM8AL board (not on both).
On the other hand, if the STM8AF or STM8AL board is used in standalone (not connected
together), they can be supplied either by the USB cable or by the external V
BAT
. As for
instance, this configuration can be used when the boards are inserted in an automotive
network.
The STM8AF and STM8AL boards include an internal 5 V to 12 V step-up converter that is
needed to build the voltages required for LIN or CAN networks. The 5 V USB is then
converted into 12 V voltage that supplies the integrated L99PM62GXP power management
IC. This device includes a 5 V regulator which is connected directly to the STM8AF5288T
microcontroller or transformed subsequently into 3.3 V to supply the STM8AL3L68T
microcontroller.
The power supplies of STM8AF5288T and STM8AL3L68T are provided by the
L99PM62GXP power management IC on condition that the microcontrollers sequentially
refresh the watchdog included in the L99PM62GXP devices. This functionality exists when
the L99PM62GXP is in Active mode (standard operation). In that case, if the L99PM62GXP
device is not refreshed periodically, the 5 V power supply is provisionally shutdown until a
next start-up sequence is performed. This behavior can generate some issues when the
SWIM communication tries to establish a connection with the microcontroller and when the
latter is not power supplied. To remedy to this situation and to avoid caring about
L99PM62GXP watchdog refresh, the L99PM62GXP can be placed in Flash mode by
configuring some dedicated jumpers (see
Section 4.2.5
). This prevents to cut the power
supply to the microcontroller as for instance for software debugging. This behavior is only
present on the STM8AF board as the STM8AL board is always put in Flash mode by design.
4.1.4
L99PM62GXP power management IC with LIN and high speed CAN
The L99PM62GXP is a power management system IC that provides electronic control units
with enhanced system power supply functionality, including various standby modes, as well
as LIN and HS CAN physical communication layers. The device's two low-drop voltage
regulators supply the system microcontroller and external peripheral loads such as sensors