LM1812 NSC | Alldatasheet
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FIGURE 1. 200 kHz Depth Sounder, 5 Feet to 100 Feet
a g 2) Absolute Maximum Ratings | it muttary/Aerospace specified devices are required, Operating Temperature OC to +70°C please contact the National Semiconductor Sales Storage Temperature Range —65C to + 150°C Office/Distributors for availability and specifications. Lead Temperature (Soldering, 10 sec) core ‘Supply Voltage, V+ (Pin 12) 18V Power Dissipation (Nots 1) 1700 mW Peak Current (Pins 6, 14) 1A Input Current (Pins 4, 8) 50 mA Electrical Characteristics v+ = 12v, T, = 25°C, unless otherwise noted Parameter [_conaitons [win [typ | mex | unite Input Sensitivity (Note 2) Figura 2 600 uVp-p Input Noise BVp-p Transmitter Output, Vga Ign tA 3 v Transmitter Output Leakage V6 = 36V mA V8 = OV Detector Output. Vsar [wer Ts Ps Detector Output Leakage views [| oor Tt Tima Transmitter Key Threshold [e=tma | oss | ov [| oe |v ‘Supply Current the mA Receive Mode Ve for Receive Mode [os Maximum Operating Frequency | TranemtMode [200 [ses | ___|__ite Tiote {: For operating al high temperatures, the L612 mut be derated Dased upon « 125°C maximum junction temperature and a thermal resistance of Se'C CW whieh apples for the device soldered ina printed crcut Board and operating in a stil air ambiant. Ove tothe low duty cycle operation, only & smal average power is dissipated inthe package. ‘Note 2: A 47k resistors acsed in parallel with the receiver tank at pin to warp variations inthe co's unloaded Q. The resator reduces sensitivity (808 equation 4) and is unnecessary in an actual sppictions circuit. Test Circuit v=o t | 1.08 m wit, TT rs Cn Ce o 22er [rent roo 100 0F - ‘TUH/7892-2 {ny = 200 KH Input eenstivty = minimum Vix for Vo to go low FIGURE 2, Sensitivity Test Circult 5-104
External Component Descriptions 2 pin_[ component |” typlcaivanes | Pin Description | Component Function
1 L1,01 500 wH-50 mH ‘Second gain stage output/ Set the operating frequency (fo) for
250 pF-2.2nF | transmitter oscillator the transmit oscillator and receiver 2 500 pF-10 nF ‘Second gain stage input Couples first and second gain stage 3 [ro | stk | _Firstgain stage output Terminates emitter-follower output
4 Input couping forthe frst gain stage
6 [is | sopti-tomt | Transmiter output ‘| Matches LM1612to the transducer pf Transmitter srver | — s [rs | _iKa-10K0 Transmitter key Current limiter for keying pulses up to 12V 9 100 nF=10 wF Receiver second stage delay | Sets the receiver turn-on delay after transmit (Figure 10) " 220nF-2.2uF — | Detector output duty cycle limit | Limits the duty cycle of the detector ‘output (short to ground to defeat) 13 100 wF-1000 »F_| Transmitter supply decoupling | Decouples the transmitter power supply
14 T14 ly = 50mH Detector output Drives neon display lamp
Ng/Np = 10 a
17 R17, C17 22k-Open Pulse integrator Controls integration time constant
10 nF=10 pe Figure 19) 18 | cite 1 nF-100 pF Pulse integrator reset Controls integrator reset time constant Figure 14, ‘TRANSDUCERS The most common transducer used with the LM1812is the ‘The LM1812 is primarily used with a single transducer per- piezo-ceramic type which is electrically similar to a quartz forming both transmit and receive functions. In this mode, crystal. Piezo-ceramic transducers are resistive at only two __-maximum echo sensitivity will occur at a frequency close to frequencies, termed the resonant and antiresonant (fy, fs) resonance. frequencies. Elsewhere these transducers exhibit some Transducer ringing isa troublesome phenomenon of singlo reactance as shown in Figure 3. transducer systems, After a transducer has been electrically driven in the transmit mode, some time is required for the ‘mechanical vibrations to stop. Depending on the amount of twoucrve damping, this ringing may last from 10 to 1000 cycles. This 3 w 1 @ mechanical ring produces an electrical signal strong enough we (200 Vp-p) to hold the detector ON, thus masking any CHAGTIVE ‘echo signals occurring during this time. A solution to this ring problem is to vary the receiver gain from a minimum, just after transmit, to a maximum, when the g ring signal has dropped below the full-gain detection thresh- | é ©) old. Since near-range echo signals are much stronger than i, ring signals, close echos will still be detected in spite of the mae ' reduced gain. sunrnee-s ‘The gain is varied by attenuating the signal between pins 2 FIGURE 2, Phase and Magnitude and 3 of the LM1612. Figure 4 shows such an arrangement. of Transducer Impedance ‘An externally generated 12V pulse (Figure 17) keys the ciency), the transducer should be operated at its resonant discharges through R, decreasing the gate voltage, which in frequency. For receiving (to maximize mechanical to electri- turn decreases the attenuation of the signal passing from || Gal etfcieney, optimum operation is at antresonance. in fim, decreagas the avlenuation of the signal passing trom | two-transducer systems the resonant frequency of the " i ‘transmit transducer is matched to the antiresonant frequen- | ey of the receiver. 5-105
to operate within a 1 mA-10 mA range. where Q = unloaded Q of L1-C1 tank. stages. instead turns ON after a slight delay as programmed by C9.
1 FROM PIN 6
FIGURE 8. Pulse Stretcher Ay = 248 FIGURE 9. Receiver Section
delays, a8 a function of the extemal component values, are -—_defeated by grounding pin 11. OFF. With the receiver OFF, no signal will be applied to the duration of the ring.
00 COMIC Cot ont {ee
FIGURE 14. integrator FIGURE 15. Typical Tranemit/Recelve Waveforms