DEMO CIRCUIT 815 LT6552 QUICK START GUIDE LT6552 3.3V Single Supply Video Difference Amplifier DESCRIPTION Demonstration circuit 815 is a Video Line-Driver & Re- tacts 7 & 8 (this pair is generally not used in Ethernet ceiver featuring the LT6552. The driver and receiver sec- datacom applications and is always straight-through). tions of the board are scored to be separable by the user Jumpers are provided in the receive section that offer 4 so that evaluation with an intermediate cable-run is read- levels of cable-loss equalization, sufficient for CAT-5 ca- ily accomplished. Figure 1 shows the general layout of ble-runs up to 1000 feet (or 11dB max 4MHz). the board and the usual connections used to perform The Performance Summary table below indicates the key evaluations. electrical characteristics provided by this evaluation The intermediate cable link may be either 75W coaxial- board. cable (such as RG-6) or twisted-pair (CAT-5 Ethernet ca- Design files for this circuit board are available. Call ble). BNC connectors are provided for the coaxial con- the LTC factory. nections, including those for the source and destination video gear. The twisted-pair option for the intermediate , LTC and LT are registered trademarks of Linear Technology Corporation. link uses RJ-45 connections and transports over con- PERFORMANCE SUMMARY Specifications are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Power Supply Range No clipping of ac-coupled video 4.0 5.0 12.6 V S I Power Supply Current 5V, video active, TX & RX total 40 mA S Z Video Input Impedance V = 1.0V 75 W INTX IN P-P Z Video Output Impedance V = 1.0V 75 W OUTRX OUT P-P Z Line-driver Output Impedance V = 1.0V unbalanced coax 75 W OUTTX OUTTX P-P V = 1.0V twisted-pair 110 OUTTX P-P Z Line-Receiver Input Impedance RX Zin jumper set to 75 ohm 75 W INRX RX Zin jumper set to 110 ohm 110 f Frequency Response, upper 3dB any EQ setting 10 MHz CU f Frequency Response, lower 3dB 5.5 Hz CL EQ Line-Receiver Equalization, EQ1=OFF, EQ2=OFF (none) 0 dB Set by Jumpers EQ1 & EQ2 EQ1=ON, EQ2=OFF, f=3.58MHz (300) 3.0 EQ1=OFF, EQ2=ON, f=3.58MHz (800) 9.0 EQ1=ON, EQ2=ON, f=3.58MHz (1000) 10.5 OPERATING PRINCIPLES The LT6552 in location U1 is used as a line-driver that stantial common-mode noise. The output is back- accepts a differential input and generates a single-ended terminated to drive either a purely unbalanced 75W coax- output in a gain-of-two configuration. The input provided ial link, or a quasi-balanced 110W CAT-5 link. The simpli- is a 75W un-balanced connection that may contain sub- fied CAT-5 output as implemented here will produce a 1 LT6552 video common-mode on the pair that may be undesirable AC-coupling on the inputs and outputs allows the circuitry in a productized realization, but helps demonstrate the to operate from single supplies down to 4V (note that in capability of the receiver function of the DC815. U1 also dc-coupled video applications, the part is useful down to demonstrates the compact DFN package. 3V). The supply and ground connections for the TX and RX sections are completely isolated so that common- The LT6552 in the U2 location (in the standard SO-8 mode ground-noise may be introduced during evaluation package) is set up similarly, except that equalization net- (up to 1.5V with 5.0V supplies). The supply current for PP works are added to provide cable-loss correction. The each section is typically 20mA with active video present. input in this receiver circuit may be terminated in either Bringing the Shutdown connection(s) to ground will bring 75 or 110 ohms, depending on the link media used. The the LT6552(s) into a low-power idle condition. output is an unbalanced 75W output, suitable for driving standard video equipment. The maximum equalization The Bill-of-Materials is shown in Figure 3 and the sche- circuitry is optimized for 1000 (300m) CAT-5 cable, pro- matic diagram of the circuitry in Figure 4. viding over 10dB of gain boost at the color sub-carrier frequency (i.e. 3.58MHz) as shown in Figure 2. QUICK START PROCEDURE Demonstration circuit 815 is easy to set up to evaluate the 7. Check for the proper RX OUT output signal. The output performance of the LT6552. Refer to Figure 1 for proper video waveform should be a high fidelity copy of the measurement equipment setup and follow the procedure original input (ac-coupled however). below: Note. The output must be properly loaded with 75W, otherwise the signal will appear doubled in amplitude. 1. Place jumpers in the following positions: 8. If longer CAT-5 cables are available, such as a full JP1 EQ2 OFF position 1000 (300m) carton with RJ-45 connectors fitted, the JP2 EQ1 OFF position EQ1 and EQ2 jumpers may be repositioned for best JP3 RX Zin 110 ohm position video reproduction. 2. With power off, connect the power supply to +5V TX and +5V RX, and the supply return to GND TX and GND 9. Evaluation may also be performed with 75W coaxial- RX. cable as the intermediate link instead of the CAT-5 twisted pair. To do this, remove the CAT-5 cable, move 3. Connect a 75W video source to TX IN (J2), such as a the JP3 jumper (RX Zin) to the 75 ohm setting, and camera or pattern generator, and assure that the signal connect the coax link from TX OUT (J3) to RX IN (J4). source is powered and active. Set the EQ1 and EQ2 jumpers for the best video repro- 4. Connect a 75W video monitor or signal analyzer to RX duction. OUT (J6), assuring that the device is powered and 10. In some instances, it may be desirable to locate the TX ready to accept video. and RX sub-circuits remote from one another to test an 5. Connect a CAT-5 patch cable from TX OUT (J1) to RX actual link, such as in an elevator car. The DC815 is IN (J5). scored to allow breaking the board into two standalone sections in order to place them separately. For short- 6. Turn on the demo circuit power supply. term tests, a 9V battery may be used as a power Note. Make sure that the input voltage does not exceed 12V. All four board source for each individual section, should powering be connections must be made to energize the entire circuitry. inconvenient otherwise. 2