ST7538P STMicroelectronics, ST7538P Datasheet - Page 17

• Manufacturer Part Number: ST7538P
• Description: Telecom Line Management ICs 1/2 Duplex FSK Modem
• Manufacturer: STMicroelectronics
• Type: Single Chipr

Specifications of ST7538P

• Product: Modem Chip
• Supply Voltage (max): 5.25 V, 12.5 V
• Supply Voltage (min): 4.75 V, 7.5 V
• Supply Current: 5 mA, 370 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Package / Case: TQFP-44
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Figure 15. Voltage and Current Feedback external interconnection Example
Voltage Control Loop Formula
Automatic Level Control (ALC)
The Automatic Level Control Block (ALC) is a variable gain amplifier (with 32 non linear discrete steps)
controlled by two analog feed backs acting at the same time. The ALC gain range is 0dB to 30 dB and
the gain change is clocked at 5KHz. Each step increases or reduces the voltage of 1dB (Typ).
Two are the control loops acting to define the ALC gain:
- A Voltage Control loop
- A Current Control Loop
The Voltage control loop acts to keep the Peak-to-Peak Voltage constant on Vsense. The gain
adjustment is related to the result of a peak detection between the Voltage waveform on Vsense and
two internal Voltage references.
- If Vsense < VCL
- If VCL
- If Vsense > VCL
The Current control loop acts to limit the maximum Peak Output current inside ATOP1 and ATOP2.
The current control loop acts through the voltage control loop decreasing the Output Peak-to-Peak
Amplitude to reduce the Current inside the Power Line Interface.
The current sensing is done by mirroring the current in the High side MOS of the Power Amplifier (not
dissipating current Sensing). The Output Current Limit (up to 370mArms), is set by means of an external
resistor (R
voltage signal. The Peak current sensing block works as the Output Voltage sensing Block:
- If V(CL) < CCL
- If CCL
- If V(CL) > CCL
Figure 15 shows the typical connection of Current anVoltage control loops.
TH
TH
- VCL
CL
- CCL
) connected between CL and PAVss. The resistor converts the current sensed into a
TH
TH
HYST
HYST
TH
TH
- CCL
+ CLC
ALC
- VCL
+ VLC
< Vsense < VCL
< V(CL) < CCL
HYST
HYST
HYST
HYST
CURRENT
VOLTAGE
LOOP
LOOP
Vout
D03IN1421
PK
TH
TH
≅
+ CCL
R
--------------------
+ VCL
1
R
ATOP/ATO
Vsense
CL
AVss
+
2
R
2
HYST
HYST
⋅
5.6nF
(
V CL
RCL
TH
R1
R2
±
Vout
V CL
The next gain level is increased by 1 step
No Gain Change
The next gain level is decreased by 1 step
Voltage Control Loop Acting
No Gain Change
The next gain level is decreased by 1 step
100pF
HYST
AV
SS
)
VCL
VCL
TH
CCL
HYST
1.865V (Typ)
CCL
TH
HYST
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