Battery Status Led - Intermec CK30 Service Manual

Chapter 4 — Theory of Operation

Battery Status LED

62
Software Low-Battery Thresholds
The first low-battery thresholds are defined in software as part of the
power management driver running on the PXA255. Temperature-
compensated battery level sampled through PSC U38 (see "Battery Status
Monitoring" on page 60) is averaged over 10 samples. When this value
falls below the software threshold, the power management code displays
the appropriate battery status icon in the icon tray. When the battery level
drops below the 0% threshold, the power management code also sends an
I2C command to the PSC to turn on the red "low-battery" LED
indication. Note that because the battery level is averaged over 10 samples
at 3-second intervals, it may take up to 30 seconds for a threshold crossing
to take effect.
The red LED remains lit until the CK30 enters the Suspend state, or the
battery level (averaged over 10 samples) rises above the software threshold.
See the next section "Battery Status LED," for more details on red LED
states.
Hardware Critical Low-Battery Threshold
As the battery level declines further, or the battery is removed, the level
crosses the hardware "critical low battery" threshold set by temperature
compensated comparator U36. This interrupts the PXA255 through signal
BATT_FAULT_IRQ* to start a Suspend and interrupts the PSC so that it
knows the PXA255 should be suspending. When the system suspends, the
processor's RESET_OUT* output is driven low, causing U42 output
BATT_FAULT* to go low. This inhibits the system from resuming until
the battery is replaced or its level rises above U36 high-going threshold
(BATT_FAULT_IRQ* goes high).
PSC U38 drives red LED D16 through Q11 D16 to display the following
battery and boot states. The power management driver running on the
PXA255 sends I2C commands to the PSC to use the red LED for low
battery indication. The PSC itself directly controls the red LED to indicate
cold boot and other power management events.
CK30 Handheld Computer Service Manual