wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 149

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

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Pre-Production
BATTERY MONITORING AND UNDERVOLTAGE LOCK-OUT (UVLO)
The WM8400 incorporates a Battery Comparator Supervisory function, which monitors the voltage on
the LINE supply pin and compares it with programmable thresholds. This feature can be used to
ensure that a suitable supply is available before enabling any dependent peripherals and also
enables the WM8400 to respond to any drops in Battery voltage. Note that a different threshold is
provided for increasing LINE voltage and for decreasing LINE voltage. The device behaviour when
the LINE voltage falls below the threshold LINE_CMP_VTHD is set using register bit
LINE_CMP_ERRACT. When the LINE voltage falls below LINE_CMP_VTHD, the associated
Interrupt Level bit LINE_CMP_LVL will be set. Unless specifically masked, this condition will also
trigger an Interrupt (IRQ) Event (see “Interrupt Events”). The LINE_CMP_LVL bit will be reset once
the LINE voltage has risen above the threshold LINE_CMP_VTHI.
It is recommended that the thresholds are set during the initial set-up programming stages
The Undervoltage Lock-Out (UVLO) circuit monitors the voltage on the LINE supply pin. An
Undervoltage condition is detected if this voltage drops below a threshold of 2.7v ±0.1v. Under this
condition, the accuracy and regulation of all the DC-DC Converters and LDO Regulators is likely to
be degraded. The device behaviour under this condition can be set using register bit
UVLO_ERRACT, as detailed in Table 97.
If an IRQ event arises from these functions, this causes the NIRQ pin to output a logic low level
(referenced to the MBVDD power domain).
Table 97 Battery Comparator and Undervoltage Lock-Out Control
The coding for the Battery Comparator threshold voltage select fields is detailed in Table 98.
Table 98 Battery Comparator Threshold Voltage Control
R78 (4Eh)
R84 (54h)
LINE_CMP_VTHD
LINE_CMP_VTHI,
REGISTER
ADDRESS
0000
0001
0010
0011
0100
0101
0110
0111
BIT
7:4
3:0
7
6
COMPARATOR
THRESHOLD
BATTERY
LINE_CMP_ERRA
CT
UVLO_ERRACT
LINE_CMP_VTHI
[3:0]
LINE_CMP_VTHD
[3:0]
2.70
2.75
2.80
2.85
2.90
2.95
3.00
3.05
LABEL
LINE_CMP_VTHD
LINE_CMP_VTHI,
DEFAULT
0111b
0100b
1000
1001
1010
1011
1100
1101
1110
1111
1b
1b
Battery Comparator Action
0 = Battery failure condition
generates IRQ only
1 = Battery failure condition
generates IRQ and initiates device
shutdown
Undervoltage Lock-Out Action
0 = UVLO generates IRQ only
1 = UVLO generates IRQ and
initiates device shutdown
Rising Threshold for LINE
comparator
2.70v to 3.45v in 50mv steps
See Table 98 for details
Falling Threshold for LINE
comparator
2.70v to 3.45v in 50mv steps
See Table 98 for details
COMPARATOR
THRESHOLD
BATTERY
DESCRIPTION
3.10
3.15
3.20
3.25
3.30
3.35
3.40
3.45
PP, April 2009, Rev 3.0
WM8400
149