U4082B Datasheet, PDF (13/30 Pages) ATMEL Corporation – Low-voltage Voice-switched IC for Hands-free Operation

U4082B
3.14
Power Supply, V_B, and Chip Disable
The power supply voltage at pin 4 (V_S) is between 3.5V and 6.5V for normal operation, but
reduced operation is possible down to 2.8V (see Figure 7-6 on page 19 and section “AGC” on
page 7). The power supply current is shown in Figure 7-9 on page 20 for both power-up and
power-down mode.
The output voltage at V_B (pin 15) is approximately (V_S – 0.7) / 2, and provides the AC ground for
the system. The output impedance at V_B is approximately 400Ω (see Figure 7-10 on page 20),
and in conjunction with the external capacitor at V_B, forms a low-pass filter for power supply
rejection. Figure 7-11 on page 21 gives an indication of the amount of rejection with different
capacitors. The capacitor value depends on whether the circuit is powered by the telephone line
or a power supply.
Since V_B biases the microphone and hybrid amplifiers, the amount of supply rejection at their
outputs is directly related to the rejection at VB, as well as their respective gains. Figure 8-1 on
page 22 depicts this graphically.
The chip disable (CD, pin 3) permits powering down the IC to conserve power and/or for muting
purposes. With CD < 0.8V, normal operation is in effect.
With 2.0V < CD < V_S, the IC is in power-down mode. In power-down mode, the microphone and
the hybrid amplifiers are disabled, and their outputs reach the high-impedance state. Addition-
ally, the bias is removed from the level detectors.
The bias is not removed from the filter (pins 1 and 2), the attenuators (pins 8, 9, 21 and 22), or
from pins 13, 14, and 15 (the attenuators are disabled, however, and will not pass a signal). The
input impedance at CD is typically 90 kΩ, has a threshold of approximately 1.5V, and the voltage
at this pin must be kept within the range of ground and V_S (see Figure 7-8 on page 20). If CD is
not used, the pin should be grounded.
4. Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Reference point pin 28, T_amb = 25° C, unless otherwise specified.
Parameters
Symbol
Value
Unit
Supply voltage, pin 4
Voltages
Pin 3, 12
Pin 13
Pin 2, 9, 21
Storage temperature range
Junction temperature
Ambient temperature range
Power dissipation
T_amb = 60° C, SO28
Maximum thermal resistance
Junction ambient, SO28
V_S
T_stg
T_j
T_amb
P_tot
R_thJA
–1.0 to +7.0
–1.0 to (V_S + 1.0)
–1.0 to (V_S + 0.5)
–0.5 to (V_S + 0.5)
–55 to +150
125
–20 to +60
520
120
V
V
°C
°C
°C
mW
K/W
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