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RM-25
System module
Voltage limits
The voltage limits of the system are listed in the following table. These are also controlling system states.
Parameter
VMSTR+
VMSTR-
VCOFF+
VCOFF-
V_BUCOFF+
V_BUCOFF-
SWCOFF
The master reset threshold controls the internal reset of UEME. If battery voltage is above VMSTR, UEME's charging
control logic is alive. Also, RTC is active and supplied from the main battery. Above VMSTR UEME allows the system
to be powered on although this may not succeed due to voltage drops during start-up. SW can also consider
battery voltage too low for operation and power down the system.
Clocking scheme
A 26 MHz VCXO is used as system clock generator in GSM. During the system start-up, UEME RC-oscillators generate
timing for state machines. All clock signals of the engine are illustrated in following figure.
Bluetooth uses a 26 MHz clock.
FM radio uses 32kHz, the SleepClk.
In SLEEP mode, the VCXO is off. UEME generates low frequency clock signal (32.768 kHz) that is fed to UPP_WD2,
Bluetooth and ZOCUS.
9235618 (Issue 2)
Description
Master reset threshold (rising)
Master reset threshold (falling)
Hardware cutoff (rising)
Hardware cutoff (falling)
Back-up battery cutoff (rising)
Back-up battery cutoff (falling)
SW cutoff limit (> regulator drop-
out limit) MIN!
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Value
2.1 V (typ.)
1.9 V (typ.)
3.1 V (typ.)
2.8 V (typ.)
2.1 V (typ.)
2.0 V (typ.)
3.4 V SW changeable
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