WM8310GEB/V Wolfson Microelectronics, WM8310GEB/V Datasheet - Page 106

• Manufacturer Part Number: WM8310GEB/V
• Description: POWER MANAGEMENT SUBSYSTEM, 169BGA
• Manufacturer: Wolfson Microelectronics

Specifications of WM8310GEB/V

• Supply Voltage: 7V
• No. Of Step-down Dc - Dc Converters: 4
• No. Of Ldo Regulators: 11
• Digital Ic Case Style: BGA
• No. Of Pins: 169
• No. Of Regulated Outputs: 13
• Operating Temperature Range: -40°C To
• Rohs Compliant: Yes
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

WM8310
17.6 BACKUP POWER
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As an option, a backup power source can be provided for the WM8310. This can either be a
rechargeable battery (coin cell or super/gold-capacitor) on the BACKUPVDD pin or else a standard
capacitor on the LDO12VOUT pin. The purpose of the backup is to power the always-on functions
such as the crystal oscillator, RTC and ALARM control registers. The backup power also maintains a
‘software scratch’ memory area in the register map - see Section 12.6. Maintaining these functions at
all times provides system continuity even when the main battery is removed and no other power
supply is available.
Backup Battery detection is enabled using BKUP_BATT_DET_ENA. The presence of a Backup
Battery connected to BACKUPVDD is indicated in the BKUP_BATT_STS field. (Note that, in the
case of a discharged battery or capacitor, the BKUP_BATT_STS may indicate that no battery is
present.)
If a backup battery is connected to the WM8310, then the backup battery charger should be
configured in accordance with the system requirements and the operating voltage of the backup
battery (or super/gold-capacitor). The backup battery charger is configured using the register bits
described in Table 57.
The backup battery charger is enabled using the BKUP_CHG_ENA bit. The target voltage and the
maximum charge current are determined by the BKUP_CHG_ILIM and BKUP_CHG_VLIM fields.
The backup battery charger operation is configurable using the BKUP_CHG_MODE field. Under
default conditions, a constant current mode is used until the target voltage is reached, after which a
constant voltage mode is selected. By setting BKUP_CHG_MODE = 1, only the constant current
mode is used, and charging stops when the target voltage has been reached. See Section 17.7 for
details of constant current and constant voltage battery charging.
The BKUP_CHG_STS field indicates whether the circuit is actively charging the backup battery. This
field may be used in conjunction with the BKUP_BATT_STS field in order to confirm if a backup
battery is present and whether charging is successful.
If desired, it is possible to connect a capacitor to the WM8310 as a backup power source, connected
via a 1kΩ resistor to the LDO12VOUT pin. In this case, however, it is particularly important to
minimise the device power consumption in the BACKUP state. A 22μF capacitor will maintain the
device settings for up to 5 minutes in ‘unclocked’ mode, where power consumption is minimised by
stopping the RTC in the BACKUP state. The RTC is unclocked in the BACKUP state if the
XTAL_BKUPENA register field is set to 0, as described in Section 20.5.
It is recommended to use a rechargeable battery as the backup power source, as this can provide
power to the WM8310 in BACKUP mode for many months whilst also maintaining the RTC and the
‘software scratch’ register.
Note that the Backup Battery Charger control registers are locked by the WM8310 User Key. These
registers can only be changed by writing the appropriate code to the Security register, as described
in Section 12.4.
R16459
(404Bh)
Backup
Charger
Control
ADDRESS
BIT
15
BKUP_CHG_ENA
LABEL
DEFAULT
0
Backup Charger Enable
0 = Disable
1 = Enable
Note - this bit is reset to 0 when the
OFF power state is entered.
Protected by user key
PP, December 2009, Rev 3.0
DESCRIPTION
Pre-Production
106