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HUAWEI MC509 CDMA LGA Module
Hardware Guide
Description of the Application Interfaces
Issue 01 (2011-04-08)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
24
For detailed information about power supply design and printed circuit board (PCB) design,
see the HUAWEI Module Power Supply Design Guide and the HUAWEI LGA Module PCB
Interconnection Design Guide
3.3.3 VCOIN Interface
VCOIN pin of MC509 module is used as backup power from the 3 V coin cell for
SMPL, RTC, and 32 kHz crystal oscillator backup; a capacitor (rather than a coin cell)
can be used if only SMPL is supported. Used as an analog output for coin cell or
capacitor charging.
Sudden momentary power loss
If the monitored VBAT drops out-of-range (<3.3V nominal), the SMPL feature may
initiate a power-on sequence without software intervention, and then VBAT returns in-
range within a programmable interval of between 0.5 and 2.0 seconds. SMPL
achieves immediate and automatic recovery from momentary power loss. A valid
voltage on VCOIN is required to run the SMPL timer. If a capacitor is used instead of
a coin, it must be connected between VCOIN and the ground. The capacitor must be
charged to operate properly as the SMPL power source. The capacitor value
depends on the SMPL timer setting.
Table 3-3 Keep-alive capacitor values vs.SMPL timer settings
SMPL timer setting
Capacitor value
Capacitor package
0.5 sec
1.5μF
0805
1.0 sec
3.3μF
0805
1.5 sec
4.7μF
0805
2.0 sec
6.8μF
1206
If the SMPL counter expires without VBAT returning to its valid range, the MC509
must undergo the normal power-on sequence whenever the VBAT is detected.
Real-time clock
If RTC is used, a manganese-lithium rechargeable battery is recommended, for
example, the SII Micro Parts HB-414 and the Panasonic ML-series. Two sets of coin
cell specifications are compared in Table 3-4 . When the MC509 is off, RTC and its
oscillator source are still active, provided by a coin cell battery which is installed. This
allows continued monitoring of RTC alarms programmed via software.