LT1684
Micropower
Ring Tone Generator
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FEATURES
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DESCRIPTIO
Allows Dynamic Control of Output Frequency,
Cadence, Amplitude and DC Offset
Active Tracking Supply Configuration Allows Linear
Generation of Ring Tone Signal
No High Voltage Post-Filtering Required
Capacitive Isolation Eliminates Optocouplers
Low Distortion Output Meets International
PTT Requirements
Differential Input Signal for Noise Immunity
User Adjustable Active Output Current Limit
Powered Directly From High Voltage Ringer
Supply—No Additional Supplies Necessary
Supply Current: < 1mA
2% Signal Amplitude Reference
Available in 14-Pin SO and DIP Packages
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APPLICATIO S
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Wireless Local Loop Telephones
Key System/PBX Equipment
Fiber to the Curb Telecom Equipment
The LT1684 receives capacitor-isolated differential PWM
input signals encoded with desired ring output cadence,
frequency, and amplitude information. The LT1684 normalizes the pulse amplitude to ±1.25V for an accurate
signal voltage reference. The cadence, frequency and
amplitude information is extracted using a multiplepole active filter/amplifier, producing the output ring tone
signal.
The LT1684 uses its own ring tone output as a reference
for generating local supply rails using complementary
high voltage external MOSFETs as dynamic level-shifting
devices. This “active tracking” supply mode of operation
allows linear generation of the high voltage ring tone
signal, reducing the need for large high voltage filtering
elements.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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The LT®1684 is a telecommunication ring tone generator.
The IC takes a user-generated pulse width modulated
(PWM) input and converts it to a high voltage sine wave
suitable for telephone ringing applications.
TYPICAL APPLICATIO
Electrically Isolated Ring Tone Generator
DC
ISOLATION
PWM
CONTROLLER
100pF
µC
P2
10k
100pF
P1
100V
6.8nF
10k
100k
GATE +
IN A
IRF610
100Ω
FB1
V+
IN B
LT1684
BGOUT
LIM +
OUT
ATREF
COMP1
1N4001
+
100pF
RING TONE
OUTPUT
0.1µF
20pF
3k
2k
5k
AMPIN
300k
4700pF
COMP2
LIM –
V–
±100mA
CAPABILITY
)
1N5817
100Ω
GATE–
1µF
–
(
IRF9610
6.8nF
100k
–100V
FB1: FERRONICS FMB1601
(716) 388-1020
1684 TA01
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