Huawei MC509 CDMA LGA manual Vcoin Interface, Sudden momentary power loss, Real-time clock

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 3-3Keep-alive capacitor values vs.SMPL timer settings

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.