MCIMX233CJM4B Datasheet, PDF (1277/1612 Pages) Freescale Semiconductor, Inc – i.MX23 Applications Processor Reference Manual

Power Supply
for proper system operation. VDDIO and VDDA are typically set once during system initialization and
not changed during operation.
32.2.1.1 Brownout/Error Detection
The power subsystem has several mechanisms active by default that safely return the device to the off
state if any one of the following errors or brownouts occur:
• The crystal oscillator frequency is detected below a certain threshold—This threshold is process-
and voltage-sensitive, but will always be between 100 kHz and 2 MHz. This feature can be disabled
in the DISABLE_XTALOK field in the HW_RTC_PERSISTENT0 register.
• The battery voltage falls below the battery brownout level (field BRWNOUT_LVL in
HW_POWER_BATTMONITOR)—This feature is disabled by clearing PWDN_BATTBRNOUT
in the same register.
• 5 V is detected, then removed—This feature is disabled by clearing
HW_POWER_5VCTRL_PWDN_5VBRNOUT.
All three mechanisms are active by default to ensure that the device always has a valid transition to a
known state in case the power source is unexpectedly removed before software has completed system
configuration. Software will typically disable the functionality of PWDN_5VBRNOUT and
PWDN_BATTBRNOUT after system configuration is complete, as shown in Figure 32-2. System con-
figuration generally includes setting up brownout detection thresholds on the supply voltages, battery,
etc. to obtain the desired system operation as the battery or power source is depleted or removed.
Typically, each output target voltage is set to some voltage margin above the minimum operating level via
the TRG field in the HW_POWER_VDDDCTRL, HW_POWER_VDDACTRL, and
HW_POWER_VDDIOCTRL registers. The brownout detection threshold is also set via the
BO_OFFSET field in the same three registers. The BO_OFFSET field determines how far the brownout
voltage is below the output target voltage for each supply and might typically be set 75–100 mV below
the target voltage. If the voltage drops to the brownout detector’s level, then it optionally triggers a CPU
Fast Interrupt (FIQ). The CPU can then alleviate the problem and/or shut down the system elegantly.
To eliminate false detection, the brownout circuit filters transient noise above 1 MHz. Any system with
an i.MX23 should include at least 33µF of decoupling capacitance on the VDDIO, VDDA, and VDDD
power rails. The capacitors should be arranged to filter supply noise in the 1-MHz and higher frequen-
cies. See Figure 32-2.
32.2.1.2 DC-DC Extended Battery Life Features
The DC-DC converter has several other power-reducing programmable modes that are useful for maxi-
mizing battery life:
• Li-Ion Buck/Boost—The Li-Ion battery configuration supports buck/boost operation, which
means that a VDDIO voltage can be supported that is higher than the input Li-Ion battery voltage.
Freescale Semiconductor
i.MX23 Applications Processor Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
32-3