DRV632
SLOS681 –JANUARY 2011
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Differential Input
Inverting Input
R2
C1
R2
C1
C3
R1
C3
R3
R1
R3
–IN
–IN
–
DRV632
+
–
DRV632
+
C2
C2
+IN
R1
R3
C3
C1
R2
Figure 7. Second-Order Active Low-Pass Filter
The resistor values should have a low value for obtaining low noise, but should also have a high enough value to
get a small-size ac-coupling capacitor. With the proposed values of R1 = 15 kΩ, R2 = 30 kΩ, and R3 = 43 kΩ, a
dynamic range (DYR) of 106 dB can be achieved with a 1-mF input ac-coupling capacitor.
INPUT-BLOCKING CAPACITORS
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
DRV632. These capacitors block the dc portion of the audio source and allow the DRV632 inputs to be properly
biased to provide maximum performance.
These capacitors form a high-pass filter with the input resistor, RIN. The cutoff frequency is calculated using
Equation 3. For this calculation, the capacitance used is the input-blocking capacitor, and the resistance is the
input resistor chosen from Table 1; then the frequency and/or capacitance can be determined when one of the
two values is given.
It is recommended to use electrolytic capacitors or high-voltage-rated capacitors as input blocking capacitors to
ensure minimal variation in capacitance with input voltages. Such variation in capacitance with input voltages is
commonly seen in ceramic capacitors and can increase low-frequency audio distortion.
1
1
fcIN
=
or
CIN =
2pRINCIN
2pfcINRIN
(3)
DRV632 UVP OPERATION
The shutdown threshold at the UVP pin is 1.25 V. The customer must use a resistor divider to obtain the
shutdown threshold and hysteresis desired for a particular application. The customer-selected thresholds can be
determined as follows:
EXTERNAL UNDERVOLTAGE DETECTION
External undervoltage detection can be used to mute/shut down the DRV632 before an input device can
generate a pop.
The shutdown threshold at the UVP pin is 1.25 V. The user selects a resistor divider to obtain the shutdown
threshold and hysteresis for the specific application. The thresholds can be determined as follows:
VUVP = (1.25 – 6 mA × R3) × (R1 + R2) / R2
Hysteresis = 5 mA × R3 × (R1 + R2) / R2
For example, to obtain VUVP = 3.8 V and 1-V hysteresis, we can use R1 = 3 kΩ, R2 = 1 kΩ, and R3 = 50 kΩ.
10
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