LT1684IN Linear Technology, LT1684IN Datasheet - Page 9

• Manufacturer Part Number: LT1684IN
• Description: IC RING TONE GENERATOR 14-DIP
• Manufacturer: Linear Technology

Specifications of LT1684IN

• Function: Tone Generator
• Number Of Circuits: 1
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 14-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Supply: -
• Voltage - Supply: -
• Power (watts): -
• Interface: -

APPLICATIO S I FOR ATIO
For applications that are extremely output ripple sensitive,
additional carrier rejection can be accomplished by modi-
fying the output filter/amplifier characteristics such as
implementing elliptical filter characteristics with a lower
cutoff frequency or implementation of additional poles.
Filter Design and Component Selection
The ring tone information represented in the low fre-
quency component of the input PWM signal is retrieved
using an active filter. This filter also generates the appro-
priate low frequency gain required to produce the high
voltage output signal and references the output to ground
(or other system reference). The frequency and gain
characteristics of this circuit element are both configurable
by the appropriate choice of external passive filter ele-
ments. Because of the active tracking supply mode of
operation, conventional active filter topologies cannot be
used. Most amplifier/filter topologies can, however, be
“transformed” into active tracking supply topologies.
Lowpass Mulitple Feedback Active Filter
Conventional Amplifier Configuration
+
–
V
IN
+
–
R1
V
U
IN
R1
R2
U
R3
C1
C2
–
+
R2
–
+
W
LOAD
LOAD
U
TRANSFORMATION
TRANSFORMATION
A conventional amplifier circuit topology can be “trans-
formed” into an active tracking supply amplifier circuit by:
a) Inverting the amplifier signal polarity (swap amplifier +
and – connections) and input source polarity.
b) Referencing all signals to the output except the feed-
back elements, which are referenced to ground (swap
output and ground).
A variety of amplifier/filter configurations can be realized
using the transformation technique. A 2-pole filter is
generally adequate for most ringer applications. Due to the
relative simplicity of infinite-gain Multiple Feedback (MFB)
configurations, these filters are good candidates for ringer
applications. Component selection and active tracking
supply transformation will be described for the following
2-pole MFB infinite-gain lowpass filter.
+
–
V
IN
Active Tracking Supply Amplifier
Active Tracking Supply Lowpass
R1
+
–
V
IN
Multiple Feedback Filter
R2
R1
C1
R3
R2
C2
–
+
–
+
LOAD
LOAD
1684 F01
LT1684
9