WM9711LGEFL/V Wolfson Microelectronics, WM9711LGEFL/V Datasheet - Page 39

• Manufacturer Part Number: WM9711LGEFL/V
• Description: Audio CODECs Stereo AC'97 CODEC with H/P
• Manufacturer: Wolfson Microelectronics

Specifications of WM9711LGEFL/V

• Number Of Adc Inputs: 1
• Number Of Dac Outputs: 1
• Interface Type: AC97
• Resolution: 12 bit
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN EP
• Minimum Operating Temperature: - 25 C
• Number Of Channels: 2 ADC/2 DAC
• Audio Codec Type: Stereo
• No. Of Adcs: 2
• No. Of Dacs: 3
• No. Of Input Channels: 9
• No. Of Output Channels: 4
• Adc / Dac Resolution: 12bit
• Adcs / Dacs Signal To Noise Ratio: 94dB
• Sampling Rate: 48kHz
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Production Data
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Figure 6 Battery Alarm Example Schematic
The typical schematic for a dual threshold battery alarm is shown above. This alarm has two
thresholds, “dead battery” (COMP1) and “low battery” (COMP2). R1, R2 and R3 set the threshold
voltages. Their values can be up to about 1MΩ in order to keep the battery current [I
(R1+R2+R3)] to a minimum (higher resistor values may affect the accuracy of the system as leakage
currents into the input pins become significant).
•
A dead battery alarm is the highest priority of interrupt in the system. It should immediately save all
unsaved data and shut down the system. The GP15, GS15 and GW15 bits must be set to generate
this interrupt.
•
A low battery alarm has a lower priority than a dead battery alarm. Since the threshold voltage is
higher than for a dead battery alarm, there is enough power left in the battery to give the user a
warning and/or shut down “gracefully”. When V
alarms are filtered out by the COMP2 delay function.
The purpose of the capacitor C is to remove from the comparator inputs any high frequency noise or
glitches that may be present on the battery (for example, noise generated by a charge pump). It
forms a low pass filter with R1, R2 and R3.
•
Provided that the cutoff frequency is several orders of magnitude lower than the noise frequency f
this simple circuit can achieve excellent noise rejection.
•
Dead battery alarm: COMP1 triggers when V
Low battery alarm: COMP2 triggers when V
Low pass cutoff f
Noise rejection [dB] = 20 log (f
V
BATT
REGULATOR
VOLTAGE
I
ALARM
c
[Hz] = 1/ (2π C × (R1 || (R2+R3)))
R1
AVDD, DCVDD, ...
R2
R3
n
/ f
C
COMP1
COMP2
c
)
BATT
BATT
BATT
gets close to the low battery threshold, spurious
< VREF × (R1+R2+R3) / R3
< VREF × (R1+R2+R3) / (R2+R3)
+
-
-
+
V
REF
DEAD
LOW
BAT
BAT
GPIO2/
IRQ
INTERRUPT
WM9711L
GPIO /
LOGIC
PD Rev 4.3 August 2006
GPIO
PINS
WM9711L
ALARM
= V
BATT
39
n
/
,