DEMO MANUAL DC2073B LTC1799, LTC6900, LTC6905, LTC6905-XXX, LTC6906, LTC6907 LTC6908 SOT23 Silicon Oscillators DESCRIPTION DC2073B demo board features Linear Technology s SOT23 Design files for this circuit board are available at packaged silicon oscillators. The DC2073B demo board is DEMO MANUAL DC2073B QUICK START PROCEDURE Test Equipment: 6. For the resistor-set ICs (DC2073B-A, -B, -C, -H, -I, -J or -K) turn the RPOT potentiometer for the desired fre- 1. A single 3V power supply. quency. (The frequency adjustment is very coarse when 2. An oscilloscope with a bandwidth of at least 5x f . the potentiometer is turned near the fully clockwise or OSC (For example, if f = 100MHz then use a 500MHz counter-clockwise position). OSC oscilloscope). Verify Oscillator Accuracy 3. A screwdriver to adjust the potentiometer. The f accuracy of the resistor-set ICs (DC2073B-A, -B, OSC Note: The DC2073B potentiometer is shorted with a -C, -H, -I, -J or -K), can be verified by setting RSET to the zero ohm resistor for factory testing. The zero ohm exact value from the f equation shown in Table 2. For OSC (RJ10) resistor must be removed to allow setting the the DC2073B-A, -B, -C, -J, -K, RSET = RPOT + RSET2. frequency with a screwdriver. If the potentiometer is RSET1 and RSET2 are never installed on the same board. set to a high value (>100k), then touching the DC2073B Connecting an ohmmeter across RPOT and RSET1 or can produce output jitter. RSET2 forces current into the IC set pin (Pin 3 or 4) and causes an error in the ohmmeter reading. The RS resistor Basic Test Procedure: is in series with RPOT and equal to RSET1 or RSET2 and + 1. Connect power supply to V and GND, turrets E4 andE5. the equivalent RSET = RPOT + RS. 2. Connect oscilloscope probe to OUT1 and GND. Procedure to Verify Oscillator Accuracy Note: The ground lead of an oscilloscope probe has a a. Calculate RSET for the desired frequency (RSET in Table 2). series inductance that can generate a resonant circuit with the probe s capacitance. Probe resonance adds b. Remove the power supply leads from DC2073B and con- + transient peaks and ringing on a high speed wave- nect an ohmmeter from POT (E6) to V (DC2073B-A, form. Reliable probing of the high frequency LTC6905 -B, -C, -J or -K) or GND (DC2073B-H or-I). and LTC6905-XXX (with corresponding demo boards C. Adjust RPOT for the exact value of RSET needed. DC2073B-A, -D, -E, -F or -G), must use a very short connection of the oscilloscope probe ground to the board Note: If the potentiometer is turned near the fully clock- GND (see probe tip picture in Figure1 Test Setup). wise or counter-clockwise position the RPOT adjustment may be too coarse for setting an exact RSET value. In 3. Set the JP1 jumper to the N divider position for the addition, for a frequency adjustment near the upper or desired frequency shown on Table2. lower f range, RSET may be greater or less than the OSC 4. Turn on supply. default DC2073B RPOT + RSET1 or RSET2 value, in this case the RSET1 or RSET2 resistor must be removed 5. The oscilloscope display shows a 3V squarewave and replaced with a lower or higher value. (0V to 3V). dc2073bfa 2