PD5019 Datasheet, PDF (9/14 Pages) List of Unclassifed Manufacturers – Telephone Ring Generator Controller

Output Amplitude Reduction Mechanism
During overload conditions, the PD5019 reduces the circuit output
voltage, while maintaining a clean sine wave, to a level that delivers
the allowed maximum output power. The protection unit counts the
number of CL pulses which are received during a single half sine
wave cycle and compares the result to an internal threshold. The
numbers of CL pulses that exceed the threshold indicate overload
conditions. Reduction of the output sine wave amplitude, in one step
resolution, is accomplished according to the following equation.
Vout peak =
VpeakNomin
al
×
16
Step
During normal operating conditions, the step number is 16. In
overload conditions, the step number can reach 31.
The amplitude can be reduced to about half of the nominal
amplitude.
In each step there will be less current limit indications.
If the overload is removed and there are no CL pulses at all, the
amplitude will begin to rise back, step by step. Each step takes one
half of a sine wave cycle.
The OHD Output that reports an overload situation is activated based
on the step number.
Reduction of the output amplitude, by more than 16 table steps, will
be indicated by OHD change to High (“1”).
When the protection unit raises the amplitude back to step 16, the
amplitude will remain at this step at least a single sine period and
this line will go back to Low (“0”).
♦ High level (OHD=”1”) means the output is overloaded.
♦ Minimum pulse length = 1 sine cycle.
♦ Maximum time for Over Load detection = ½ sine cycle time,
(30mS at 16.7Hz ringing frequency).
♦ Over load required duration, for detection = ½ sine cycle time.
This line can be useful for overload problem reports in medium size
ringers, and can be used for off hook detection in small size ringers
when there are few telephones connected to one line.
Output Shut Down
If the output load of the ring generator is high, and the output
amplitude has reached its minimal level, an internal counter will start
to count 300mS.
If the overload has not been removed after 300mS, the protection will
shut down the PWM for 4.86 sec.
After the shutdown period, the PD5019 will begin operating at
minimum amplitude level.
If there are still CL pulses, the internal counter will start to count
300mS again and shut down for 4.86 sec again.
However if the load is removed after the shutdown period, the output
amplitude will start to increase, step by step.
Vin
T1
PD5019
PWM OUT
CL
100 OHM
VCC
R2
1KΩ
1
R3
Vin
U1A
8 LM339
3
+
-²
REF
4
Q1
BUK 582-100 A
C18
1nF 50 V
R1
PD5019
TELEPHONE RING GENERATOR CONTROLLER
♦ Maximum amplitude reduction/incremental
response time = ½ sine cycle time.
♦ Time for overload shut down = (8 • sine cycle time)+300mS.
Max.
♦ Shut down period = 4.86Sec.
Timing accuracy is derived from the main oscillator frequency
accuracy.
DETERMINING THE OUTPUT AMPLITUDE
The topology of the ring generator is an open loop flyback. In this
topology, the output amplitude is determined by the PWM duty cycle.
The PD5019 changes its PWM duty cycle according to an internal
sine wave reference table and a known mathematical transfer
function.
To determine the maximum amplitude of the output sine wave, use
the following equation:
Voutrms = (2.773 • n) • ( ^{R1 + R2} )
R2
♦ R1 and R2 are the voltage divider resistors used in the Vin
sampling A/D.
♦ n is the winding turn ratio of the transformer.
♦ It is recommended to change the output voltage amplitude by
changing R1 or R2 while using the typical rated n. A high-
resolution potentiometer can be used to obtain the proper
resistor values during the circuit design.
CHOOSING n:
1. Define the input voltage range.
2. Calculate the average input voltage according to the following
equation.
Vin min+Vin max
Vin mid =
2
3. Choose the parameter nVin according to the following table.
Parameter
Min.
Recommended
Max.
nVin
42
48
54
4. Calculate n (winding turns ratio) according to the following
equation.
nVin (choosed from the table)
n=
Vin mid
ADJUSTING OUTPUT AMPLITUDE WITHOUT A/D
When the input voltage sampling the A/D is not used (CAD_In = ”0”),
the maximum output amplitude is determined according to the input
voltage and turns ratio.
Vout rms = 1.4731• n • Vin
Note: When the input voltage sampling A/D is not used, the CAD_In
terminal must be grounded.
PWM_Out: This is the PWM output signal. This output is capable of
directly driving a FET.
Typical current sense circuit configuration
PD5019
US Patent No.
5,828,558