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LT1684 Micropower Ring Tone Generator
FEATURES
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DESCRIPTIO
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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
The LT(R)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. 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.
APPLICATIO S
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Wireless Local Loop Telephones Key System/PBX Equipment Fiber to the Curb Telecom Equipment
TYPICAL APPLICATIO
PWM CONTROLLER P1 C P2 DC ISOLATION 100pF
Electrically Isolated Ring Tone Generator
100V 6.8nF IN A 10k IN B LT1684 LIM + OUT ATREF COMP1 GATE + FB1 V+ 1N4001 100 100k IRF610
10k
100pF
100pF 0.1F
BGOUT 3k 2k 300k 1F 5k AMPIN 4700pF
20pF COMP2 LIM - V- GATE- 6.8nF 1N5817
100 IRF9610 100k -100V
FB1: FERRONICS FMB1601
(716) 388-1020
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+
RING TONE OUTPUT
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(
100mA CAPABILITY
)
1684 TA01
1
LT1684
ABSOLUTE
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RATI GS
Voltages: Active Tracking Differential Voltage (GATE + - GATE -) ..................................- 0.3V to 42V Local Supply Differential Voltage (V + - V -) ...............................................- 0.3V to 36V Local Supply Voltage V + .............. (GATE + - 7.0V) to (GATE + + 0.3V) Local Supply Voltage V - .............. (GATE - - 0.3V) to (GATE - + 7.0V) PWM Input Differential Voltage (IN A - IN B) .........................................- 7.0V to 7.0V PWM Input Voltage Common Mode ................. (V - - 0.3V) to (V + + 0.3V) LIM + Current Limit Pin Voltage ..................... (OUT - 0.3V) to (V+ + 0.3V) LIM- Current Limit Pin Voltage .................... (V - - 0.3V) to (OUT + 0.3V) All Other Pin Voltages ........... (V - - 0.3V) to (V + + 0.3V)
PACKAGE/ORDER I FOR ATIO
TOP VIEW IN B COMP1 COMP2 LIM - V- GATE
-
1 2 3 4 5 6 7
14 IN A 13 BGOUT 12 AMPIN 11 GATE + 10 V + 9 8 LIM + OUT
ATREF
N PACKAGE 14-LEAD PDIP
S PACKAGE 14-LEAD PLASTIC SO
TJMAX = 125C, JA = 75C/W (N) TJMAX = 125C, JA = 115C/W (S)
Consult factory for Military grade parts.
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(Note 1)
Currents: LIM +, LIM - Current .......................................... - 350mA OUT Current ....................................................... 350mA BGOUT Current .................................................... 10mA PWM (IN A, IN B) Current .................................... 5mA GATE +, GATE - Current ....................................... 20mA COMP1 Current .................................................... 1mA COMP2 Current .................................................... 1mA ATREF Current ..................................................... 20mA Temperatures: Operating Junction Temperature Range Commercial Grade ................................. 0C to 125C Industrial Grade ................................ - 40C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1684CN LT1684CS LT1684IN LT1684IS
LT1684
ELECTRICAL CHARACTERISTICS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V + - V - = 20V, Voltages referenced to pin OUT, VOUT = VATREF unless otherwise noted.
SYMBOL IS |V +| |V -| VGATE+ VGATE - PARAMETER DC Supply Current (Note 2) Local Supply Voltages Active Tracking Supply FET Bias Voltage Active Tracking Supply FET Bias Voltage Input Carrier Frequency Minimum Valid Differential Input Differential Input Threshold | IN A - IN B | RIN RINA,INB BG Buffer VBGOUT VBGOUTOS IBGOUTSC RBGOUT tr tf tr-f tpr tpf tp BGOUT Normalized Voltage Output Offset Voltage [(VBGOUT+) + (VBGOUT -)]/2 BGOUT Short-Circuit Current BGOUT Output Impedance BGOUT Rise Time (10% to 90%) BGOUT Fall Time (10% to 90%) BGOUT RiseTime - Fall Time BGOUT Propagation Delay PWM Input Transition to 10% Output (Rising Edge) BGOUT Propagation Delay PWM Input Transition to 90% Output (Falling Edge) BGOUT Propagation Delay Rising Edge - Falling Edge OUT Offset Voltage OUT Output Impedance OUT Short-Circuit Current VAMPIN = 0v, IOUT = 0A RAMPIN = 10k (Note 4) -10mA ILIM+ -100mA, LIM + Shorted to OUT 10mA IOUT 100mA, LIM - Shorted to V - LIM + Shorted to OUT LIM - Shorted to V -
q
CONDITIONS IN A - IN B 1.6V VGATE+ V + VGATE- V - IGATE+ = -100A, ATREF = 0V IGATE- = 100A, ATREF = 0V
q q q q
MIN
TYP 680
MAX 950
UNITS A V
Supply and Protection 6.5 13.2 -14.8 10 14.0 -14.0 14.8 -13.2
V V
PWM Receiver fPWM VIN 10 IN A - IN B or IN B - IN A
q q
kHz V 1.00 V k k
1.6 0.50 7 50 0.70 10
Differential Input Overdrive Impedance (Note 3, 5) Single-Ended Input Impedance (Note 5)
VIN > VTH + 100mV To Pin OUT
q q
Magnitude |VBGOUT|
q q q
1.235 1.225 -7 -10 2
1.250 1.250
1.265 1.275 7 10
V V mV mV mA
4.5 0.2 160 260 300 400 0 500 600 100
- 2mA IBGOUT 2mA ROUT = 5k, COUT = 10pF ROUT = 5k, COUT = 10pF ROUT = 5k, COUT = 10pF ROUT = 5k, COUT = 10pF
q q q q q q
ns ns ns ns ns ns
- 200
-100 340 440
- 200
-100
Output Amplifier VOUTOS ROUT IOUTSC
q
-6 -8 0.01 0.15 100 190
6 8
mV mV mA
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: IC Supply current specification represents unloaded condition and does not include external FET gate pull up/down currents (GATE +, GATE - pins). Actual total IC bias currents will be higher and vary with operating conditions. See Applications Information.
Note 3: PWM inputs are high impedance through 100mV beyond the input thresholds. Note 4: 10k resistor from pin AMPIN to ground. Note 5: Guaranteed but not tested.
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LT1684 TYPICAL PERFOR A CE CHARACTERISTICS
DC Supply Current vs V+ - V-
740 720 TJ = 25C 710 690 IN A - IN B 1.6V
VGATE - VATREF (V)
DC SUPPLY CURRENT (A)
DC SUPPLY CURRENT (A)
700 IN A - IN B 1.6V 680 660 640 620 600 14 16 18 20 V + - V - (V) 22 24
1684 G01
IN A - IN B -1.6V
VGATE - VATREF Voltage Magnitudes vs Temperature
14.5 14.4 14.3 IGATE = 1mA 0.85 0.80 0.75
VGATE - VATREF (V)
IN A - IN B (V)
14.2 14.1 14.0 13.9 13.8 13.7 13.6 13.5 - 50 -25 0 25 50 75 TEMPERATURE (C) 100 125
0.70 0.65 0.60 0.55 0.50 0.45 - 50
VBGOUT (V)
PWM Buffer (Pin BGOUT) Current Limit vs Temperature
6.0 250 225 200 175 150 125
PWM BUFFER CURRENT LIMIT (mA)
5.5
OUTPUT CURRENT LIMIT (mA)
OUTPUT CURRENT LIMIT (mA)
5.0 4.5 4.0 3.5 3.0 2.5 2.0 - 50
-25
0 25 50 75 TEMPERATURE (C)
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100
DC Supply Current vs Temperature
14.3
VGATE - VATREF Voltage Magnitudes vs IGATE
TJ = 25C 14.2
670 650 630 610 590 570 550 -50 IN A - IN B -1.6V
14.1
14.0
13.9
-25
0 25 50 75 TEMPERATURE (C)
100
125
13.8 0.1
0.3
1.0 IGATE (mA)
3.0
10.0
1684 G03
1684 G02
PWM Input Thresholds vs Temperature
1.253 1.252 1.251 1.250 1.249 1.248 1.247 1.246
VBGOUT Magnitude vs Temperature
-25
0 25 50 75 TEMPERATURE (C)
100
125
1.245 - 50
-25
0 25 50 75 TEMPERATURE (C)
100
125
1684 G04
1684 G05
1684 G06
Output Amplifier Current Limit vs Temperature (RLIM = 0)
200
Output Amplifier Current Limit vs External Limiting Resistor Values
150
100 TYPICAL (TJ = 25C) 50 MINIMUM (TJ = 125C) 0
125
100 - 50
-25
0 25 50 75 TEMPERATURE (C)
100
125
0
1
2
3
456 RLIM ()
7
8
9
10
1684 G07
1684 G08
1684 G09
LT1684
PI FU CTIO S
IN B (Pin 1): PWM Negative Input. Input is isolated from digital source by ~100pF series capacitor. A 10k resistor can be connected to the IN B pin in series with the isolation capacitor for transient protection. The PWM receiver implements a diode forward drop of input hysteresis (relative to IN A). This hysteresis and internal signal limiting assure common mode glitch rejection with isolation capacitor mismatches up to 2:1. For maximum performance, however, effort should be made to match the two PWM input isolation capacitors. Pin IN B is differentially clamped to pin IN A through back-to-back diodes. This results in a high impedance differential input through 100mV beyond the input thresholds. 5k internal input resistors yield a 10k (nominal) differential overdrive impedance. COMP1 (Pin 2): Output Amplifier Primary Compensation. Connect a 100pF capacitor from pin COMP1 to pin OUT. COMP2 (Pin 3): Output Amplifier Secondary Compensation. Connect a 20pF capacitor from pin COMP2 to pin OUT. LIM - (Pin 4): Output Amplifier Current Sink Limit. Pin implements IOUT * R = VBE current clamp. Internal clamp resistor has a typical value of 3.5. For maximum current drive capability (190mA typical) short pin to pin V -. Reduction of current sink capability is achieved by placing additional resistance from pin LIM - to pin V -. (i.e. An external 3.5 resistance from pin LIM - to pin V - will reduce the current sinking capability of the output amplifier by approximately 50%.) V - (Pin 5): Local Negative Supply. Typically connected to the source of the active tracking supply P-channel MOSFET. V - rail voltage is GATE - self-bias voltage less the MOSFET VGS. Typical P-channel MOSFET characteristics provide ATREF - V - 10V. GATE- (Pin 6): Negative Power Supply FET Gate Drive. Pin sources current from pull-down resistor to bias gate of active tracking supply P-channel MOSFET. Self-biases to a typical value of -14V, referenced to pin ATREF. Pull-down resistor value is determined such that current sourced from the GATE - pin remains greater than 50A at minimum output signal voltage and less than 10mA at maximum output signal voltage. ATREF (Pin 7): Active Tracking Supply Reference. Typically connected to pin OUT. Pin bias current is the difference between the magnitudes of GATE + pin bias and GATE- pin bias (IATREF = IGATE + - IGATE -). OUT (Pin 8): Ring Tone Output Pin. Output of active filter amplifier/buffer. Used as reference voltage for internal functions of IC. Usually shorted to pin ATREF to generate reference for active tracking supply circuitry. Connect a 1A (1N4001-type) diode between V + and OUT and a 1A Schottky diode from V - to OUT for line transient protection. LIM+ (Pin 9): Output Amplifier Current Source Limit. Pin implements IOUT * R = VBE current clamp. Internal clamp resistor has a typical value of 3.5. For maximum current drive capability (190mA typical) short pin LIM + to pin OUT. Reduction of current source capability is achieved by placing additional resistance from pin LIM + to pin OUT. (i.e. An external 3.5 resistance from pin LIM + to pin OUT will reduce the current sourcing capability of the output amplifier by approximately 50%.) V + (Pin 10): Local Positive Supply. Typically connected to the source of the active tracking supply N-channel MOSFET. This condition should be made using a ferrite bead. Operating V + rail voltage is GATE + self-bias voltage less the MOSFET VGS. Typical N-channel MOSFET characteristics provide V + - ATREF 10V. GATE + (Pin 11): Positive Power Supply FET Gate Drive. Pin sinks current from pull-up resistor to bias gate of active tracking supply N-channel MOSFET. Self-biases to a typical value of 14V, referenced to pin ATREF. Pull-up resistor value is determined such that sink current into GATE + pin remains greater than 50A at maximum output signal voltage and less than 10mA at minimum output signal voltage. AMPIN (Pin 12): Output Amplifier Input. Connected to external filter components through series protection resistor (usually 5k). Thevenin DC resistance of external filter and protection components should be 10k for optimum amplifier offset performance. See Applications Information section.
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LT1684
PI FU CTIO S
BGOUT (Pin 13): Normalized PWM Buffered Output. PWM differential input is amplitude normalized to 1.25V (referenced to the OUT pin). This signal is used to drive the active filter/amplifier. Filter resistor values must be chosen to limit the maximum current load on this pin to less than 2mA. The output is current limit protected to a typical value of 4.5mA. IN A (Pin 14): PWM Positive Input. Input is isolated from digital source by ~100pF series capacitor. A 10k resistor should be connected to the IN A pin in series with the isolation capacitor for transient protection. The PWM receiver implements a diode forward drop of input hysteresis (relative to IN B). This hysteresis and internal signal limiting assure common mode glitch rejection with isolation capacitor mismatches up to 2:1. For maximum performance, however, effort should be made to match the two PWM input isolation capacitors. Pin IN A is differentially clamped to pin IN B through back-to back isolation-base diodes. This results in a high impedance differential input 100mV beyond the input thresholds. 5k internal input resistors yield a 10k (nominal) differential overdrive impedance.
FUNCTIONAL BLOCK DIAGRA
100pF
+
PWM INPUT 100pF
10k
IN A
5k V+
-
10k
IN B
5k -1.25V V+
BGOUT
COMP1 100pF FILTER ELEMENTS COMP2
20pF
RING OUTPUT (RING RETURN) V-
1684 BD
6
+
AMPIN
5k
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-
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1.25V
GATE + 14V 15k ATREF LIM +
CURRENT LIMIT 14V
OUT
GATE - LIM - V-
LT1684 Block Diagram
LT1684
OPERATIO
BASIC THEORY OF OPERATION The LT1684 operates using a user-provided pulse-widthmodulated (PWM) digital signal as input*. The low frequency modulation component of this signal represents the desired output waveform. Changing the PWM input can thus dynamically control the frequency, cadence, amplitude and DC offset of the desired output. This method of sine wave generation can accomodate all popular ring tone frequencies including 17Hz, 20Hz, 25Hz and 50Hz. The LT1684 receives the PWM input by a capacitorisolated differential input at pins IN A and IN B. This signal is amplitude normalized by a bandgap reference and output single-ended on the BGOUT pin such that the PWM carrier is 1.25V about the voltage on the OUT pin. The low frequency component of the normalized PWM signal is recovered using an active filter circuit constructed using an onboard driver amplifier. This amplifier also provides current drive for the final ring tone output. The ring tone output is used as the reference for a floating active biasing scheme by pin ATREF. As the ring tone output rises and falls through its typical range of hundreds of volts, the LT1684 "tracks" the output signal, maintaining local supply voltages across the IC of approximately 10V. Input Receiver/Reference Buffer The differential receiver for the PWM input signal requires minimum differential input levels of 1.6V to assure valid change-of-state. The receiver inputs are capacitor coupled, isolating the LT1684 from the PWM generator. The receiver is leading edge triggered. The input receiver controls a switched-state output that forces an amplitude normalized voltage (referenced to the OUT pin) of 1.25V that follows the PWM input. This switched voltage is driven off-chip on pin BGOUT. When the IN A input is driven higher than IN B (by the required
* Contact Linear Technology for code.
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(Refer to Functional Block Diagram)
1.6V), the reference drives BGOUT to +1.25V above OUT. When IN B input is driven higher than IN A, BGOUT is forced to -1.25V relative to OUT. The amplitude normalized representation of the input PWM signal is used as the input for the active filter element and output driver. Output Amplifier/Driver The normalized PWM signal output on the BGOUT pin is converted to the final ring tone signal by an active filter. This filter consists of an onboard amplifier and a few external components. Although many different types of filters can be constructed, a 2-pole Multiple Feedback (MFB) configuration generally provides adequate performance and is desirable due to its simplicity and effectiveness. The low frequency component of the 1.25V PWM signal contains the desired ring tone frequency and cadence information. The MFB active filter strips this information from the PWM signal and amplifies this low frequency component to generate the final desired output. Active Tracking Supplies Implementation of the active tracking supply technique enables linear generation of the ring tone output, and takes advantage of the intrinsic supply noise immunity of a linear amplifier, reducing the need for large high voltage filtering elements. Two external power MOSFETs act as voltage level-shifting devices and generate the power supply voltages for the LT1684. The LT1684 uses its own output as a voltage reference for the FET level shifters, "suspending" itself (by these generated supply voltages) about the signal output. In this manner, the LT1684 can linearly generate a signal hundreds of volts in amplitude at its output, while maintaining 10V local supply rails across the IC itself.
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LT1684
APPLICATIO S I FOR ATIO
Encoded PWM Signal Input Basics
The LT1684 accepts a user-supplied PWM carrier that represents the desired output ring tone signal. This PWM input is normalized by the LT1684 such that ring tone output amplitudes can be accurately encoded into the PWM input. The LT1684 accepts a differential input to maximize rejection of system transients and ground noise. If no differential signal is readily available from the PWM controller, a simple inverter/buffer block can be used to create the differential signal required. Each differential input is internally connected through a 5k series resistor to back-to-back isolation-base diodes. These devices internally clamp the differential input signal to 100mV greater than the input comparator hysteresis range. The input comparator toggles with a differential hysteresis equal to that of a standard diode forward voltage (0.7V nominal). As such, the differential impedance of the input remains high throughout the input hysteresis region, then reduces to a nominal value of 10k (7k minimum) as the input is overdriven beyond the comparator input threshold. A minimum differential input of 1.6V is specified to assure valid switching. The PWM signal can be visualized in terms of instantaneous ring tone amplitude, normalized to the LT1684 amplitude reference. For a given desired output voltage VOUTN, the input pulse train required follows the relation: VOUTN = 2 * VREF * (DC - 0.5), or DC = [VOUTN / (2 * VREF)] + 0.5, where: VREF = 1.25V normalized peak voltage DC = PWM input duty cycle
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A 10% to 90% duty cycle range is a practical limit for a 10kHz input carrier. This corresponds to normalized signal amplitude of 1V. Duty cycles exceeding this range can cause increased output signal distortion as signal energy is lost due to finite rise and fall times becoming a significant percentage of the signal pulses. The associated reduction in the pulse energy manifests itself as a "soft clipping" of the output signal resulting in an increase in harmonic distortion. The normalized PWM signal is amplified to the desired output signal level by the active filter/amplifier stage. Thus, dividing the desired peak output amplitude by the peak normalized encoded amplitude (VOUT/VOUTN) yields the required DC gain of the active filter. System Considerations Assuming use of a 10% to 90% maximum PWM range, the peak normalized signal will be: VPWM(pk) = 0.8 * VREF = 1.0V, and: VOUT(pk) = VPWM(pk) * Filter DC Gain Thus, the DC gain of the output filter equals the desired peak voltage of the output ring tone signal. The frequency characteristics of the lowpass output filter must reflect the allowable carrier ripple on the output signal. For example, a 10kHz carrier system could use a 2-pole Butterworth lowpass with a cutoff frequency of 100Hz. This filter provides 40dB of input signal rejection at 10kHz yielding 25mVP-P output ripple. If the DC gain of the output filter/amplifier was 100, the output ripple voltage would be riding on a 100V sine wave, and therefore be about - 78dB relative to the output ring signal.
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LT1684
APPLICATIO S I FOR ATIO
For applications that are extremely output ripple sensitive, additional carrier rejection can be accomplished by modifying 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 frequency component of the input PWM signal is retrieved using an active filter. This filter also generates the appropriate 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 elements. 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.
Conventional Amplifier Configuration
R1 R2
+
VIN
VIN TRANSFORMATION
-
LOAD R2
Lowpass Mulitple Feedback Active Filter
Active Tracking Supply Lowpass Multiple Feedback Filter +
VIN C1 R1 R2 R3 C2
1684 F01
-
+
VIN
C1
LOAD
+
+
-
R1
-
TRANSFORMATION
-
R2
C2 R3
+
+
-
R1
-
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A conventional amplifier circuit topology can be "transformed" 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 feedback 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.
Active Tracking Supply Amplifier +
LOAD LOAD
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LT1684
APPLICATIO S I FOR ATIO
C2 = mC1 m 1 / [4Q2(1+|HO|)] 2nC1mQ R1 = R2 / |HO| R3 = Example: 1 n2C12R2m
The component selections for the active tracking supply lowpass MFB filter configuration follow the relations: R2 = 1 [1-4mQ2(1+|HO|)]1/2
FILTER GAIN (dB)
Conditions: Output ring tone peak voltage = 100V Ring frequency = 20Hz Input duty cycle range = 10% to 90% Filter Q = 0.707 Set: Choose: Then: fn = n / 2 = 100Hz C1 = 1.0F (a convenient value) m [4(0.7)2(1+100)]-1 .005 C2 = mC1 (sets m = 0.0047) R2 = 1 [1- 4(0.0047)(0.707)2(101)]1/2 (4100)(1e-6)(.0047)(0.707) R2 = 300k R1 = 300k/100 R1 = 3.0k R3 = [(2100)2(1e-6)2(300k)(0.0047)]-1 R3 = 2k This filter configuration yields a DC Gain of 100, a corner frequency of just under 100Hz with gain reduction of only 0.1% at 20Hz, and a 10kHz carrier rejection of greater than 40dB at the output. Active Tracking Supply Components Given the previous discussion, implementation of an active tracking supply system may seem almost trivial. C2 = 4700pF
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Active Tracking Supply Lowpass Multiple Feedback Filter Transfer Characteristic (AV vs fn)
50 0 -50 1 10 100 1K HERTZ (Hz) 10K 100K
1684 F02
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However, bootstrapping an amplifier system about its own output creates a complex myriad of inherent stability and response issues. Attempting such a configuration with generic "jelly-bean" components is not recommended for the faint of heart or type-A personalities. The LT1684, however, makes for a simplistic approach to active tracking component selection. The high voltage MOSFET transistors used in the circuit must have an operating VDS specified at greater than the corresponding high voltage supply rail plus the opposite maximum excursion of the output signal. For example, if a system is designed with a 240V supply (+ 120V, -120V) and outputs a ring signal that has a 100V peak amplitude, the MOSFET VDS ratings must be greater than 240/2 + 100 = 220V. Active Filter Tuned Oscillator-- No PWM Input Required A simple yet effective method of producing a high quality sine wave is to place a high-Q bandpass filter and a hard limited gain element in a positive feedback loop. This circuit will oscillate at the bandpass frequency, producing a sine wave at the filter output. The product of the fundamental component of the limiter and the filter gain at the bandpass frequency determines the output amplitude. This type of circuit is commonly referred to as an active filter tuned oscillator.
LT1684
APPLICATIO S I FOR ATIO
Active Filter Tuned Oscillator Block Diagram
1684 F03
The LT1684 can be implemented easily into a telephone ringer circuit based on the active filter tuned oscillator topology, eliminating the need for a user-supplied PWM input signal. The LT1684's active filter amplifier can be used as a high-Q bandpass filter element by configuring it as an active tracking supply bandpass. The LT1684's controlled output receiver/buffer is also convenient for use as the hard limiter. Because the LT1684 receiver/ buffer requires a true differential input for proper operation, a dual comparator IC such as the LT1017 must be bootstrapped along with the LT1684 to provide differential control signals. The LT1017 and LT1684 receiver/ buffer combine to create a high gain hard limiter whose
Bandpass MFB Filter
CF2 RF3 RF1 CF1
+
VIN
-
RF2 VOUT
-
+
1684 F4a
Active Tracking Bandpass MFB Filter
-
RF1 RF2 CF1 VIN
+
-
VOUT
+
1684 F5b
CF2
RF3
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output is controlled to 1.25V. The LT1684 active bandpass filter is then connected as a positive feedback element with the limiter component, which completes the active filter tuned oscillator topology. The active bandpass filter circuit is easily configured using a basic MFB bandpass configuration, however, the active tracking supply technique used by the LT1684 requires "transformation" of this topology. This "transformation" swaps the amplifier signal polarity, references all signals to the output, and references all feedback elements to ground as described previously in the Filter Design and Component Selection section. The design equations for the active tracking bandpass filter are the same as the pretransformation MFB topology, such that if CF1 = CF2 = C: RF1 = Q/(O * C *H0) RF2 = Q/(2Q2 -H0)(O * C) RF3 = 2Q/(O * C) Example: Conditions: Output peak voltage = 95V Ring frequency = 20Hz Bandpass Q = 9.4 A square wave with peak amplitude A has a fundamental component with amplitude 4A/, where A = 1.25V. Therefore, the desired filter's bandpass gain HO = 95/(4 * 1.25/) ~ 60. Given capacitor values C = 0.22F (a convenient value) and desired filter characteristics of: Q = 9.4, HO = 60, O = 2(20Hz), then: RF1 = 5.6k, RF2 = 2.7k, RF3 = 680k. The amplitude, frequency and envelope response time of the output signal can be adjusted by simply changing the values of resistors RF1 to RF3 accordingly. This produces a high voltage, high quality 20Hz sine wave at the filter output with a peak amplitude of 95V. Differential amplitude and frequency characteristics are achieved by simply changing a few resistor values. The output of the LT1684 is internally current limited to a minimum of 100mA peak, allowing this ring tone generation circuit to be used with loads up to 7 REN with no degradation of the output waveform.
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LT1684
APPLICATIO S I FOR ATIO
110V 8 7 V 1/2 LT1017 V- 4
+
Active Filter Tuned Oscillator Ring Tone Generator
+ -
5 8 6 R9 10k 1 V 1/2 LT1017 V- 4
+
C2 100pF
R10 10k 1 2 C1 20pF 3 4
IN B COMP1 COMP2
IN A BGOUT AMPIN
14 13 12 11
R8 10k
LT1684 GATE + LIM - V- GATE - ATREF V+ LIM + OUT
D1 1N5817
5 6 7
10 9 8 RF3 680k CF1 0.22F RF1 5.6k C4 6.8nF C5 0.1F
CF2 0.22F RF2 2.7k C3 6.8nF
-110V FB1: FERRONICS FMB1601 (716) 388-1020
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+ -
3 R6 1k R5 100k 2 R3 100k R2 100 M1 IRF610 FB1 D2 1N4001
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OUTPUT
-
(
100mA PEAK
)
R1 100 R4 100k
M2 IRF9610
1684 F05a
Ringer Output
5V-15V to Ring Tone Fully Isolated Converter Using an Active Filter-Tuned Oscillator Circuit
D4 MURS160
*
2 C9 0.47F 160V C14 10F 160V R2 10k 1 OUT A -IN A +IN A VEE 2 5, 6 D2 MURS160 C12 0.47F 160V C15 10F 160V R8 100k 1 IN B COMP1 COMP2 AMPIN 11 FB1 5 V- GATE - ATREF 6 R11 50k 7 V+ LIM + OUT 10 9 8 RF3 680k CF1 0.22F RF1 5.6k CF2 0.22F RF2 2.7k C1 6.8nF C2 6.8nF LT1684 LIM - GATE + 12 BGOUT 13 IN A 14 2 C5 20pF 3 4 OPTO1 H11AG1 6 5 1 DZ2 R10 91V 10k DS1 1N5817 C6 100pF R3 10k R1 1k 4 VCC OUT B -IN B +IN B LT1017 8 7 6 5 C11 0.47F 160V
TYPICAL APPLICATIO S
1
5V TO 15V INPUT
+
12
C7 220F 10V
*
+
3
7, 8
*
9 4
11
DZ1 44V
D3 1N4001
R4 10k R7 100k R6 100
C8 1nF
R9 39
M1 IRF610
5 DS2 MBRS1100 1
C4 1F
VIN
SW
4
LT1270
D1 1N4001 C3 0.1F
2
FB
GND VC 4 2
+
OUTPUT
3
-
C13 0.01F OPTO2 H11AG1 6 5 R13 50k R12 10k 1 DZ4 91V
C10 0.1F
R15 2k 4 2 (716) 388-1020
R5 100 R14 100k
M2 IRF9610
1684 TA03
FB1: FERRONICS FMB1601
LOAD (REN) V (PEAK) RF1 RF2 RF3 7 5.6k 2.7k 680k 95V 10 6.8k 3.3k 620k 70V
U
LT1684
T1 COILTRONICS 14239-X3
+
13
LT1684
TYPICAL APPLICATIO S
5kW PWM-to-Analog Converter
120V 1nF MTP2N50E FB1 V+ 10 2 100pF 180H 20pF 2k 2 VIN 3.9k
6800pF
100k 100
1000pF PWM IN
11 10k 14 GATE+ IN A
1000pF
10k
COMP1 1 IN B LT1684 BGOUT
13 3k 2k 5k
ATREF COMP2 LIM- GATE- V-
12
AMPIN
300k
0.1F
470pF
6800pF
6
100k 2N3904 -120V 100 2N3904 47 FB1: FERRONICS FMB1601 (716) 388-1020
14
U
47 100 2N3906 2N3906 100 IRF230 1 VTOP SENSE+ 8 1k ILIM+ LT1166 VOUT ILIM- 180H SENSE- VBOTTOM 4 100 MTP2N50E 100 1nF IRF9240 -100V 3 1F 6 1k 5 0.22 7 1F 0.22 1H 5kW LOAD 0.22 100V
9 LIM+ OUT 8 7 3 4 5
TYPICAL POWER SLICE (1 OF 13 IN PARALLEL)
1684 TA04
LT1684
PACKAGE DESCRIPTIO
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381) 0.005 (0.125) MIN 0.100 (2.54) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. BSC MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) +0.035 0.325 -0.015 +0.889 8.255 -0.381
(
)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0 - 8 TYP
0.016 - 0.050 (0.406 - 1.270)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
Dimensions in inches (millimeters) unless otherwise noted. N Package 14-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.770* (19.558) MAX 14 13 12 11 10 9 8
0.255 0.015* (6.477 0.381)
1 0.130 0.005 (3.302 0.127) 0.020 (0.508) MIN
2
3
4
5
6
7
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076)
N14 1098
S Package 14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 - 0.344* (8.560 - 8.738) 14 13 12 11 10 9 8
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1
2
3
4
5
6
7
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483) TYP
0.050 (1.270) BSC
S14 1298
15
LT1684
TYPICAL APPLICATIO
VIN 5V
C2 100pF
+
PWM INPUT C1 100pF
-
C3 100pF
R4 10k IN B LT1684 COMP1 BGOUT IN A
R2 10k R10 100k R3 5k COMP2 AMPIN
C4 20pF
LIM -
GATE + FB1
V-
V+ D1 1N4001
C8 1F
GATE -
LIM + R5 300k C5 4700pF
ATREF
OUT R6 3k C6 6.8nF 160V
FB1: FERRONICS FMB1601
RELATED PARTS
PART NUMBER LT1082 LT1166 LTC1177-5/LTC1177-12 LT1270 LT1271 LT1339 LT1676 DESCRIPTION 1A High Voltage Switching Regulator Power Output Stage Automatic Bias System Isolated MOSFET Drivers 8A Power Switching Regulator 4A Power Switching Regulator High Power Synchronous DC/DC Controller Wide Input Range, High Efficiency, Step-Down Switching Regulator COMMENTS VIN = 3V to 75V, SW Voltage = 100V Sets Class AB Bias Currents, Eliminates Adjustments and Thermal Runaway 2500VRMS Isolation, UL Recognized VIN = 3.5V to 30V, IQ = 7mA VIN = 3.5V to 30V, IQ = 7mA Operation Up to 60V, Output Current Up to 50A Operation Up to 60V, 100kHz, Up to 500mA Output
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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5V Input Nonisolated 5 REN Ring Generator
100V D2 MURS160T3 T1 COILTRONICS CTX 14468-X1 12 10 9 7
+
C11 0.47F 160V C10 0.47F 160V D3 MURS160T3
*
+
R8 100 M1 IRF610
*
4, 5
+
* 1, 2
C12 220F 35V
U1 R1 2k 4 C7 6.8nF 160V DS1 MBRS1100 DZ1 60V MMSZ5264BT1 SW VIN 5 R12 5k
1
LT1271 VC GND 3 FB
2
R11 470 C9 0.1F
R7 100 M2 IRF9610
R9 100k -100V R16 1M
R15 12k
D4 D1N4148
LT1211 1 2 3 4 OUT A -IN A +IN A VEE VCC OUT B -IN B +IN B 8 7 6 5 R13 12k
1684 TA02
D5 D1N4148
R14 1M
DS2 D1N5817 (716) 388-1020
C13 0.1F RING TONE OUT
1684f LT/TP 0300 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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