SIM225 Technical Reference Manual
28
© Serious Integrated, Inc.
SIM225_TRM_A1ENUS
Revision A1
discussed, this port should supply 500mA to power the board. On the schematics, this supply is denoted
+5V_USBF
.
In the USB-only powered mode the SIM225’s total power is limited to 500mA: only the extra power not
consumed by the SIM225 will be available for battery charging. This may result in long charge times.
Turning the SIM225 off (via the
PWRDWN#
signal) or turning the LCD backlight off will reduce the needed
current by the SIM225 and provide up to 500mA of current to charge the battery.
Normally when the SIM225 is incorporated in a production product it is powered from an external power
supply, most commonly through the
Power and Communications Connector
or the
Baseboard Connector
.
The
+5V_EXT
signal available on these and other connectors should be supplied with an externally
reg5VDC supply. Without the optional LiPo battery, an 850mA supply is sufficient. With the
battery 1300mA is recommended (850mA + 450mA charging current).
Note that if both
+5V_USBF
and
+5V_EXT
are present the BQ24030 can pull from both supplies
simultaneously, but will always give preference to the external
+5V_EXT
supply if present. This is called
Dynamic Power Path Management (DPPM) and is fully documented in the
BQ24030 data sheet
.
+5V_MAIN ON NON-LIPO VARIANTS
On variants without Lithium Ion Polymer battery support, the power supply system is significantly simpler.
These variants will be powered by either
+5V_USBF
or
+5V_EXT
whichever is
higher
in voltage.
The two signals are routed to the
+5V_MAIN
signal through two protection diodes. These diodes are low-
forward-drop Schottky type and capable of a full 1A continuous current; nevertheless, the
+5_VMAIN
signal will typically be 0.3V below the higher of the two input voltages.
This configuration allows, for example, a SIM225 powered in a device via
+5V_EXT
to simultaneously have
a PC USB port or USB hub connected to the SIM.
MAIN 3.3V REGULATION
Major power consumers, such as the
USB Host
,
LCD panel backlight power
, and
audio
are all derived from
+5V_MAIN
to maximize power conversion efficiency. The rest of the circuitry on the SIM225, including
MCU, memories, and LCD screen require a +3.3V supply.
The
+5V_MAIN
power is converted to 3.3VDC (the
+3V3
signal) through a switching power supply at
typically 90%+ efficiency. Some variants use the
National/TI LMZ10501 Simple Switcher
(capable of
delivering up to 1.0A) and others the
Intersil ISL9104
(500mA maximum output current).
+3V3
is also delivered to the
Baseboard Connector
, the
Power and Communications Connector
, and the
FFC Expansion Connector
, but is only meant to supply a small amount of power to an attached system.
The amount of 3.3VDC power available to these connectors is limited by (a) the total capacity of the
regulator and (b) the excess power available on the +3V3 signal after calculating the incoming available
power minus that used on the SIM225. The
DC Power Characteristics
information in this manual can assist
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