U4090B-P Datasheet, PDF (6/35 Pages) ATMEL Corporation – Monolithic Integrated Feature Phone Circuit EMI Improved

Table 2-1. Pin Description (Continued)
Pin
Symbol Function
30
TLDR Time constant of receive level detector
31
AGA
Automatic gain adjustment with line current, a resistor connected from this pin to GND sets the starting
point, maximum gain change: 6 dB.
32
IREF
Internal reference current generation; RREF = 62 kΩ; IREF = 20 µA
Sidetone reduction output
33
STO
Output resistance approximate: 300Ω,
Maximum load impedance: 10 kΩ.
34
VM
Reference node for microphone-earphone and loudspeaker amplifier, supply for electret microphone
(IM ≤ 700 mA)
Three-state mute input
1. Normal operation
35
MUTR ^{2. Mute for ear piece}
3. Mute for RECIN signal
Condition of earpiece mute is stored
36
RECO2 Inverting output of receiving amplifier
37
STIS
Input for sidetone network (short loop) or for answering machine
38
STIL
Input for sidetone network (long loop)
39
RAC
Input of receiving amplifier for AC coupling in feedback path
40
RECO1 Output of receiving amplifier
41
GR
A resistor connected from this pin to GND sets the receiving amplification of the circuit; amplifier RA1 can
be muted by applying VMP to GR
42
TTXA Time constant of anti-clipping in transmit path
43
RECIN Input of receiving path; input impedance is typically 80 kΩ
44
TXIN
Input of intermediate transmit stage, input resistance is typically 20 kΩ
Note: Filters against electromagnetic interference (EMI) are located at following pins: MIC1, MIC2, RECIN, TXIN, STIS, STIL and
RAC.
3. DC Line Interface and Supply-voltage Generation
The DC line interface consists of an electronic inductance and a dual-port output stage which
charges the capacitors at V_MPS and V_B. The value of the equivalent inductance is given by:
L = R_SENSE × C_IND × ((R_DC × R₃₀)/(R_DC + R₃₀))
In order to improve the supply during worst-case operating conditions, two PNP current sources
- I_BOPT and I_MPSOPT - hand an extra amount of current to the supply voltages when the NPNs in
parallel are unable to conduct current.
A flowchart for the control of the current sources (Figure 3-2) shows how a priority for supply
VMPS is achieved.
6 U4090B-P
4741C–CORD–11/05